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Various strategies have evolved to protect animals from predators. We explored the activity and predation risk experienced by two species of aphid. Both species will drop from plants when disturbed and face a suite of predators, including wolf spiders, when they reach the ground. We focused on Aphis fabae Scopoli and Aphis nerii Boyer de Fonscolombe (Hemiptera: Aphididae, Aphidini); A. nerii sequesters cardiac glycosides when it feeds on milkweed. We explored the interactions between these aphids and the wolf spider Pardosa milvina Hentz (Araneae: Lycosidae) that is likely a predator they encounter when they are not on their host plants. We hypothesized that there would be differences in the susceptibility of the two species to predation and that the more vulnerable species would react more strongly to substrate‐borne cues deposited by the spider. We predicted that any behavioral reactions that the aphid displayed in response to predator cues would be effective in reducing risk. We documented the activity of each aphid species on chemotactile cues from P. milvina and measured predation rate in arenas with and without those same cues. Aphis fabae altered their activity in the presence of P. milvina cues but A. nerii did not. Likewise, A. fabae was more susceptible to predation by P. milvina when no cues were present, but when cues were present, predatory success was much lower. Aphis nerii, the less desirable prey for this predator, moved less and had a different locomotory pattern than A. fabae in control trials with no spider cues and so we cannot determine whether its chemical protection or activity were more important in reducing predation levels. These results provide insight into the risks faced by aphids when they are off of their host plant and in a barren environment. [ABSTRACT FROM AUTHOR]

The response of herbivorous insects to plant drought stress can range from positive to negative, and it has been challenging to understand the causes of this variation. We tested whether plant trait values associated with aridity gradients might underlie this variation and how such effects vary between two insect feeding guilds.Here, we propose that plants trait values associated with adaptation to arid environments would result in positive effects of experimental drought on herbivores, with such plant species adaptively shifting resources away from resistance to maintain performance under stress. In contrast, plants with trait values associated with adaptation to mesic environments would result in negative effects of drought because such species lose vigour and thus decrease their host quality.We tested these predictions using experimental manipulations in 13 milkweed species (genus Asclepias) adapted to a wide range of environmental conditions and the herbivore performance of a specialist leaf‐chewer (monarch butterfly; Danaus plexippus) and sap‐feeder (oleander aphid; Aphis nerii). We exposed plants to physiologically calibrated species‐specific watering regimes to maximize (100%) or reduce (50%) stomatal conductance and then monitored herbivore performance.The effects of drought stress on herbivore survival ranged from strongly positive (50% increase) to strongly negative (80% decrease) among milkweed species, but these effects were inconsistent between the two herbivores.Plant trait values associated with adaptation to aridity were correlated with monarch survival in the predicted manner, such that milkweed species with high water‐use efficiency (WUE) and low relative water content (RWC) increased monarch survival under drought. In contrast, aphid survival was unrelated to arid‐adapted trait values.Drought‐induced changes in plant quality were negatively associated with both herbivore survivals. Specifically, milkweed species that increased cardenolides concentration under drought conditions decreased monarch and aphid survival.Synthesis. We demonstrated that the indirect effects of drought on herbivores varied tremendously among closely related plant species and between co‐occurring insect herbivores. We in turn present evidence that some of this variation is explained by plant traits associated with adaptation to arid versus mesic environments for leaf‐chewers but not sap‐feeders and that such effects are mediated by drought‐induced changes in chemical defences. [ABSTRACT FROM AUTHOR]

Predatory efficiency of Eupoedes corollae predator's larvae toward densities of 25, 50, 75, 100 insect of Aphis gossypii and of Aphis nerii, a study was carried out of the laboratory in growth chamber with a temperature of 24±1 C◦ and 70 ± 10 % RH and photoperiod 12: 12 hours. The results showed that the predator E. corollae larvae consumption in different percentage according to the prey's species and the number provided, and that 50 density of cotton aphid was the best in the daily and total consumption of E.corollae predator, in addition to the relatively low development period of predator larvae at the same density. The average of consumption of the predator's larvae instars was proportional to the different densities of the aphids 25, 50.75 and 100 insect, as it reached to ( 84.64, 143.16, 170.9 and 217.93) of cotton aphid and (56.23, 110.67, 124.78 and 148.16) insects of oleander aphid, respectively. The average of aphid is estimated at 154.2 and 110.2 insect, respectively, for the two species with significant differences between them. [ABSTRACT FROM AUTHOR]

India has a rich source of biodiversity of medicinal plants, which serves as a source of livelihood for a large Indian population. For the past several decades, most of the research works on medicinal plants have been focused on isolating their active ingredient and preparing a suitable commercial formulation while completely neglecting their conservation. Very few studies have been done to understand the factors, especially biotic ones that limit the yield of medicinal plants. Therefore, the present study aims at studying the nature of the damage, severity of the injury, and population dynamics of Aphis nerii and its natural enemy (Cheilomenes sexmaculata) on madhunashini, Gymnema sylvestre at ICAR-Directorate of Medicinal and Aromatic Plants Research, Anand (Gujarat) India along with the study of weather parameters affecting pest population during two years from 2018–20. The percent incidence and severity of A. nerii ranged from 0 to 100 percent and 0 to 4, respectively. The peak population (275.56 and 293.31/10 cm twig) was recorded at the 6th SMW (Standard Meteorological Week) in both the observed years. The occurrence of C. sexmaculata started during the first fortnight of November, and peak population was recorded during the 6th SMW. During the study period, the aphid population was negatively correlated with all the density-independent factors. The different concentrations of neem oil (10000 ppm) like 0.25, 0.50, and 0.75 percent were used to test the efficacy during the peak insect activity period. Our study suggests that neem oil spray (10000 ppm) @ 0.75 percent could effectively manage the aphid population in field conditions. [ABSTRACT FROM AUTHOR]

Abstract Parasitoids used as biological control agents often parasitize more than a single host species and these hosts tend to vary in suitability for offspring development. The population dynamics of parasitoids and hosts may be altered by these interactions, with outcomes dependent on the levels of suitability and acceptance of both host species. Parasitism of individuals of an unsuitable host species may indirectly increase populations of a suitable host species if eggs laid into unsuitable hosts do not develop into adult parasitoids. In this case, the unsuitable host is acting as an egg sink for parasitoids and this can reduce parasitism of suitable hosts under conditions of egg limitation. We studied parasitoid‐mediated indirect interactions between two aphid hosts, Aphis glycines (the soybean aphid) and A. nerii (the milkweed, or oleander aphid), sharing the parasitoid Aphelinus certus. While both of these aphid species are accepted by A. certus, soybean aphid is a much more suitable host than milkweed aphid is. We observed a drastic reduction of parasitoid offspring production (45%) on the suitable host in the presence of the unsuitable host in microcosm assays. Aphelinus certus females laid eggs into the unsuitable hosts (Aphis nerii) in the presence of the suitable host leading to egg and/or time limitation and reduced fitness. The impact of these interactions on the equilibrium population sizes of the three interacting species was analyzed using a consumer–resource modeling approach. Both the results from the laboratory experiment and the modeling approaches identified apparent predation between soybean aphid and milkweed aphid, in which milkweed aphid acts as a sink for parasitoid eggs leading to an increase in the soybean aphid population. The presence of soybean aphids had the opposite effect on milkweed aphid populations as it supported increases in parasitoid abundance and thus reduced the fitness and abundance of this aphid species.

Drought is an important stressor that affects plant growth, survival and physiology and, through plant responses, alters plant–herbivore interactions and herbivore population dynamics. Short‐term drought can occur at different times during a growing season, affecting herbivore populations and plants at various stages of development and growth. As phenology influences drought response, drought timing could strongly structure plant–herbivore interactions. We grew common milkweed plants with or without its dominant aphid herbivore, allowing both plants and herbivore populations to develop over time as in a typical growing season. To determine how drought timing affects plants and aphid populations, we applied short‐term (1 week) drought at different times. Plants and aphids were sensitive to drought timing, with a few weeks difference shifting the effects of drought from minimal to causing massive declines in plant growth, plant survival and herbivore population density. Aphid herbivory added to or overrode drought consequences in plants, with different plant fitness components responding distinctly to herbivory. Drought timing also affected whether plant and herbivore responses were parallel or divergent, suggesting that shifts in the seasonal timing of drought have the potential to disrupt plant–herbivore interactions and affect the larger ecological community. Our results show drought timing has important and disparate consequences for herbivores and their host plants and indicates the necessity of considering phenology and timing in assessing drought response. [ABSTRACT FROM AUTHOR]

In many organisms, phenotype and fitness are strongly influenced by both current environmental factors and maternal effects. The low genetic variation, high phenotypic plasticity, and telescoping generations seen in aphids permit us to investigate the relative importance and potential interaction of maternal and current environments on phenotype. Although past studies have identified an influence of maternal host plant on offspring phenotype and reproduction in aphids, few have demonstrated the potential for these maternal effects to also interact with the aphid's current environment. By rearing multiple generations of Aphis nerii (Fonscolombe) (Hemiptera: Aphididae) on their host common milkweed, Asclepias syriaca (L.) (Apocynaceae), we tested the relative influence and interaction of both maternal and current environmental effects of crowding and plant quality on aphid body size and reproduction. Our results indicate that aphid body size increased with current plant quality and decreased with aphid density in both generations, with an additional direct, positive relationship between body size and fecundity. We did not find evidence for adaptive maternal effects, e.g., production of fewer, larger, offspring by stressed mothers. Instead, poor maternal environments constrained aphid body size and reproduction. Importantly, these adverse maternal effects were only seen in offspring where subsequent nymph population growth was allowed to increase unchecked, likely reducing available resources. Our study thus demonstrates that the significance of maternal effects in aphid development and reproduction can depend on current resource availability, shaping the phenotype and fecundity of offspring under stressful conditions. Incorporating this framework for how aphid body size and reproduction respond to current and maternal environments may improve predictions for how aphid population growth is impacted by resource limitation across generations. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to report the presence of a new pest on the territory of Romania. The new species identified is Aphis nerii (Boyer de Fonscolombe, 1841), also known as oleander aphid or milkweed aphid, is included in the Order Hemiptera, Suborder Sternorrhyncha, Family Aphididae. The origin of the species is uncertain, although it is attributed as an area of origin the Mediterranean Basin, considered the area of origin of its main host plant (Oleander - Nerium oleander). Aphis nerii is a cosmopolitan species (Africa, Asia, Europe, North America, Australia-Oceania, South America. Milkweed aphids are also present on the European continent, being a relatively new species, most reports being recorded after 2013. The presence of milkweed aphid in Europe can be associated with the introduction of the invasive species Asclepias syriaca. Aphis nerii is a polyphagous species, attacking ornamental, cultivated and spontaneous plant species from 19 families (Apocynaceae, Fabaceae, Caricaceae, Crassulaceae, Euphorbiaceae, Solanaceae, Rutaceae, Compositae, Convolvulaceae, Vitaceae, etc.). The observations made on the Romanian territory, in 2020, highlighted the presence of the species Aphis nerii on the plants of Asclepias syriaca (common milkweed). The damage caused by aphid milkweed is expressed by the qualitative depreciation of the plants, delays of the plant growth, the production of honey dew and improving the occurrence of phytopathogenic fungi. The information presented, regarding polyphagism and damages caused by Aphis nerii, is enough to conclude that it is necessary to study this species in Romania, to establish the spread, host plants, damages caused and as well to investigate proper control methods. [ABSTRACT FROM AUTHOR]

Microorganisms in insects play pivotal roles in various aspects, including nutrition, development, protection, physiology, and behavior. Aphids, a distinct group of insects that feed on plant sap, have been the focus of research exploring the intricate relationships between microbes and insects. While extensive investigations have delved into the obligate endosymbionts in aphids, there remains a gap in understanding the diversity of gut microbes and other associated microorganisms. This study employed culture-dependent methods to isolate microorganisms from diverse aphid species (Aphis gossypii, A. nerii, A. craccivora , Hysteroneura setariae , and Myzus persicae). The results identified three bacterial phyla (Firmicutes, Proteobacteria, Actinobacteria), belonging to families such as Bacillaceae, Corynebacteriaceae, Micrococcaceae, Morganellaceae, Staphylococcaceae, and Xanthomonadaceae. Bacillus emerged as the predominant taxon, with Aphis craccivora exhibiting both high abundance and an even distribution of bacteria. Both A. craccivora and A. gossypii displayed a diverse array of bacterial species, with A. gossypii exhibiting the highest dominance index. Hysteroneura setariae showcased a diverse dominance of bacteria among aphids. Notably, the microorganisms Exiguobacterium indicum MPB-2 and Pseudomonas hibiscicola CCF 2-2 demonstrated the ability to degrade imidacloprid at a rate of 18–22%. This finding emphasizes their capacity to utilize insecticides as sole sources of carbon and nitrogen, ultimately benefiting the fitness of the insects. This study contributes to our understanding of the microorganisms presented in aphids. Highlighting the efficacy of culture-dependent methods in unveiling the diversity of these microscopic organisms. • Unveiling microbe-insect relationships in sap-feeding aphids. • Diverse gut microorganisms explored beyond endosymbionts. • Microbes isolated from various aphid species. • Firmicutes, Proteobacteria, Actinobacteria identified in aphids. • Exiguobacterium indicum and Pseudomonas hibiscicola break down imidacloprid. [ABSTRACT FROM AUTHOR]

Interactions between herbivores and their predators are shaped, in part, by plant phenotype. Consequently, ubiquitous symbionts of plants below‐ground, such as arbuscular mycorrhizal fungi (AMF), may influence interactions above‐ground between predators and their prey by altering plant phenotype. However, the ecological relevance of below‐ground organisms on predator–prey interactions under field conditions remains unclear.We assessed how AMF influence herbivore–predator interactions through a field experiment.We planted two milkweed species (Asclepias curassavica and Asclepiasincarnata) provided with different amounts of AMF inoculum (zero, medium, and high) in a randomized block design. We added aphids to plants and reduced predator pressure weekly for 5 weeks to evaluate effects of AMF on predator recruitment. We then allowed herbivore–predator interactions to re‐establish naturally for the remainder of the season to examine whether AMF‐mediated variation in predator recruitment influenced the suppression of aphid populations.Arbuscular mycorrhizal fungi availability in soils mediated interactions between predaceous aphid midge flies Aphidoletes aphidimyza and their aphid prey Aphis nerii, but the effects were plant species‐specific. On A. curassavica, by mid‐season, midges were recruited most strongly on plants under medium AMF availability and least on plants under high AMF availability. In contrast, each midge killed fewer aphids with increasing aphid density on medium AMF plants, but killed more aphids with increasing aphid density on high AMF plants. In combination, aphid mortality rates imposed by midges were greatest on medium AMF plants, followed by high and zero AMF plants. By comparison, on A. incarnata, the recruitment of midges was strongest on high AMF plants and weakest on medium AMF plants. AMF had no effect on the number of aphids killed per midge, relative to aphid density, so mortality rates of aphids imposed by midges mirrored recruitment. Rates of decline in aphid populations following predator recolonization were associated with midge densities, as well as lacewing and syrphid densities, which were unaffected by AMF availability. Therefore, the effects of AMF on aphid population decline were not a simple function of AMF–midge interactions.Our findings demonstrate that the availability of AMF in soils has pervasive, but complex, effects on predator–herbivore dynamics in the field. [ABSTRACT FROM AUTHOR]

Sphaerophoria rueppellii is a commercially available syrphid used for control of numerous agricultural and ornamental aphid pests. Previous research has shown that prey species can affect some of the biological traits of beneficial insects, which might affect their success and establishment, but such effects are completely unknown for this predator. The present work explored the effects of two polyphagous aphid species which are common agricultural pests in vegetables and cereal crops (Myzus persicae and Rhopalosiphum padi, respectively) and one ornamental pest (Aphis nerii), on some fitness-related parameters of S. rueppellii, when fed exclusively with one of these species during the larval stage. Fecundity and fertility of females was higher when they were fed with R. padi and showed the lowest values with A. nerii. Egg-to-adult survival and adult's wing length were also shorter when syrphid larvae ate the latter species, which might be related to the aphid's host plant toxicity, the ornamental Nerium oleander. These results will help to improve the use of this predator with regards to the targeted aphid pest and the affected plants. [ABSTRACT FROM AUTHOR]

1. Although preference–performance relationships in insects are typically studied in a bi‐trophic context, it is well known that host plants can affect both the preference and performance of natural enemies of herbivorous insects. 2. This study presents evidence from field and laboratory studies that two species of milkweeds, the putatively less defended Asclepias incarnata and the putatively more defended Asclepias syriaca, differentially affect adult oviposition and larval performance in Aphidoletes aphidimyza, an aphid‐feeding predatory midge, independent of aphid density. 3. Host plant species affected predatory fly larvae abundance by a factor of 50 in the field and a factor of 8 in the laboratory. Larval and adult emergence rates in our laboratory studies provided strong evidence for reduced performance on A. syriaca. Oviposition in choice and no‐choice settings provided some evidence for preference for A. incarnata, and a potentially suppressive effect of A. syriaca. 4. The results provide limited support for the hypothesis that natural selection can lead to positive correlations between adult oviposition preferences and larval performance upon various food sources, even when predatory insects oviposit onto host plants of their herbivorous prey. 5. Preference and performance are not perfectly aligned in this system, however, because ovipositing females do not reject A. syriaca entirely. Potential explanations for mismatches between preference and performance in this system include the neural constraints associated with being a generalist, adaptive time‐limited foraging strategies, and unique evolutionary histories of laboratory colonies compared with wild insects. [ABSTRACT FROM AUTHOR]

The generalist predator, green lacewing, Chrysoperla carnea Stephens (Neuroptera: Chrysopidae) has a key role in integrated pest management (IPM) strategies for many crop pests. The influence of different prey types has been studied to strengthen the C. carnea. Current in-vitro study was made to figure out the effects of different prey on mortality and certain biological characteristics of C. carnea. The highest mortality rate (66.43±2.13%) was for larvae, which fed upon Oleander aphid, Aphis nerii. Less larval mortality (7.86±2.37%), larval period (164.57±8.16 h), maximum pupal weight (9.86±0.41 mg) and emergence (95.13±2.03%) was observed when C. carnea was provided with eggs of Sitotroga cerealella. Bervicornye brassicae was performed well than A. nerii but was found least successful as compared to eggs of S. cerealella. Both aphid species were significantly good in performance when fed to C. carnea larvae with S. cerealella eggs than their solo effect. Results depicted that mortality factor and life parameters of C. carnea larvae are influenced by its prey type which they fed on. These results of the study could be used to improve the rearing and conservation strategies to increase C. carnea population and their predatory activities. [ABSTRACT FROM AUTHOR]

We investigated prey preference of adult male and female Propylea dissecta (Mulsant) when fed on the aphids, Aphis craccivora and Lipaphis erysimi, which sequester toxic allelochemicals from their host plants. Both the male and female adults of P. dissecta prefer to consume L. erysimi in most mixed diet treatments (cafeteria experiment). This was well supported by significantly high values of the β and C prey preference indices. However, when provided with these aphids separately, the adults showed no significant difference in aphid consumption, regardless of the species of aphid and sex of the adult ladybird. We conclude that host plant allelochemicals/toxicants have a direct effect on prey preference of ladybirds. Host plant toxic constituents can alter the biochemical composition of the most preferred prey and make them the least preferred. Mixing two toxic similar diets can make one diet more suitable than the other.

Plants use volatile organic compounds (VOCs) to cue natural enemies to their herbivore prey on plants. Simultaneously, herbivores utilize volatile cues to identify appropriate hosts. Despite extensive efforts to understand sources of variation in plant communication by VOCs, we lack an understanding of how ubiquitous belowground mutualists, such as arbuscular mycorrhizal fungi (AMF), influence plant VOC emissions. In a full factorial experiment, we subjected plants of two milkweed (Asclepias) species under three levels of AMF availability to damage by aphids (Aphis nerii). We then measured plant headspace volatiles and chemical defenses (cardenolides) and compared these to VOCs emitted and cardenolides produced by plants without herbivores. We found that AMF have plant species-specific effects on constitutive and aphid-induced VOC emissions. High AMF availability increased emissions of total VOCs, two green leaf volatiles (3-hexenyl acetate and hexyl acetate), and methyl salicylate in A. curassavica, but did not affect emissions in A. incarnata. In contrast, aphids consistently increased emissions of 6-methyl-5-hepten-2-one and benzeneacetaldehyde in both species, independent of AMF availability. Both high AMF availability and aphids alone suppressed emissions of individual terpenes. However, aphid damage on plants under high AMF availability increased, or did not affect, emissions of those terpenes. Lastly, aphid feeding suppressed cardenolide concentrations only in A. curassavica, and AMF did not affect cardenolides in either plant species. Our findings suggest that by altering milkweed VOC profiles, AMF may affect both herbivore performance and natural enemy attraction. [ABSTRACT FROM AUTHOR]

The use of chemical insecticides has had several side-effects, such as environmental contamination, foodborne residues, and human health threats. The utilization of plant-derived essential oils as efficient bio-rational agents has been acknowledged in pest management strategies. In the present study, the fumigant toxicity of essential oil isolated from Satureja intermedia was assessed against cosmopolitan stored-product insect pests: Trogoderma granarium Everts (khapra beetle), Rhyzopertha dominica (Fabricius) (lesser grain borer), Tribolium castaneum (Herbst) (red flour beetle), and Oryzaephilus surinamensis (L.) (saw-toothed grain beetle). The essential oil had significant fumigant toxicity against tested insects, which positively depended on essential oil concentrations and the exposure times. Comparative contact toxicity of S. intermedia essential oil was measured against Aphis nerii Boyer de Fonscolombe (oleander aphid) and its predator Coccinella septempunctata L. (seven-spot ladybird). Adult females of A. nerii were more susceptible to the contact toxicity than the C. septempunctata adults. The dominant compounds in the essential oil of S. intermedia were thymol (48.1%), carvacrol (11.8%), p-cymene (8.1%), and γ-terpinene (8.1%). The high fumigant toxicity against four major stored-product insect pests, the significant aphidicidal effect on A. nerii, and relative safety to the general predator C. septempunctata make terpene-rich S. intermedia essential oil a potential candidate for use as a plant-based alternative to the detrimental synthetic insecticides.

1. Specialized insect herbivores commonly co-opt plant defences for protection against predators, but the costs, benefits and mechanisms of sequestration are poorly understood. 2. We quantified sequestration of toxic cardenolides by the specialist aphid Aphis nerii when reared on four closely related milkweed (Asclepias) species with >20- fold variation in cardenolide content, and in the presence or absence of generalist ladybug predators. 3. Increasing concentrations of apolar plant cardenolides increased sequestered amounts in aphids. High concentrations in plants impaired aphid population growth, but also reduced the top-down effects of predators. An in vitro enzymatic assay of total cardenolides in aphid bodies using the cardenolides' target (animal Na+/K+-ATPase) revealed that the subset of sequestered cardenolides is disproportionally more toxic than cardenolides in leaves. 4. All aphids accumulated two cardenolides not present in their host plant, even on plants with very low foliar cardenolide concentrations. Sequestration of potent cardenolides by A. nerii thus involves passive, concentration-dependent uptake from the host plant, as well as a presumably more active mechanism of modification and up-concentration of plant cardenolides. 5. The concentration of toxins in the host plant thus not only determines the negative impacts on growth and performance of an aphid, but also the ease and efficiency by which toxins are sequestered for the aphid's defence, making the costs and benefits of plant toxins highly context-dependent for both the plant and the herbivore. Therefore, variation in plant toxins is of central importance for coevolutionary plant-insect interactions, particularly in environments with variable predator pressure. [ABSTRACT FROM AUTHOR]

Abstract: Studies of plant defenses and insect herbivores have been important in the development of our understanding of coevolution and specialization. Milkweed–herbivore systems have been a model for studying plant secondary chemistry defense evolution, insect adaptations to that chemistry, and coevolution between toxic plants and their herbivores for over a century. Yet, we are only beginning to unravel the multitude of adaptations required for insect specialization on milkweed plants. We review the empirical evidence for specialist insect adaptations toward milkweed toxins, coevolution between insects and milkweed plants, and canonical paradigms for sequestration and highlight the areas for further research. By comparing research performed with diverse milkweed insects, we discuss the need to comprehensively study adaptations and specialization in divergent insect taxa. [ABSTRACT FROM AUTHOR]

Predictable effects of resource availability on plant growth-defense strategies provide a unifying theme in theories of direct anti-herbivore defense, but it is less clear how resource availability modulates plant indirect defense. Ant-plant-hemipteran interactions produce mutualistic trophic cascades when hemipteran-tending ants reduce total herbivory, and these interactions are a key component of plant indirect defense in most terrestrial ecosystems. Here we conducted an experiment to test how ant-plant-hemipteran interactions depend on nitrogen (N) availability by manipulating the presence of ants and aphids under different N fertilization treatments. Ants increased plant flowering success by decreasing the densities of herbivores, and the effects of ants on folivores were positively related to the density of aphids. Unexpectedly, N fertilization produced no changes in plant N concentrations. Plants grown in higher N grew and flowered more, but aphid honeydew chemistry stayed the same, and neither the density of aphids nor the rate of ant attraction per aphid changed with N addition. The positive effects of ants and N addition on plant fitness were thus independent of one another. We conclude that N was the plant's limiting nutrient and propose that addition of the limiting nutrient is unlikely to alter the strength of mutualistic trophic cascades. [ABSTRACT FROM AUTHOR]

We investigated prey preference of adult male and female Propylea dissecta (Mulsant) when fed on the aphids, Aphis craccivora and Lipaphis erysimi, which sequester toxic allelochemicals from their host plants. Both the male and female adults of P. dissecta prefer to consume L. erysimi in most mixed diet treatments (cafeteria experiment). This was well supported by significantly high values of the ß and C prey preference indices. However, when provided with these aphids separately, the adults showed no significant difference in aphid consumption, regardless of the species of aphid and sex of the adult ladybird. We conclude that host plant allelochemicals/toxicants have a direct effect on prey preference of ladybirds. Host plant toxic constituents can alter the biochemical composition of the most preferred prey and make them the least preferred. Mixing two toxic similar diets can make one diet more suitable than the other. [ABSTRACT FROM AUTHOR]

Chitosan and its derivatives have received attention as alternatives to pesticides in agriculture. Insects are a good source for chitosan isolation. In the present study, chitosan was obtained from Chrotogonus trachypterus (Orthoptera, Acrididae), and its N-alkyl derivatives were synthesized. Experiments were conducted to assay their aphicidal activity against three aphid species. All derivatives had a higher aphicidal action (> 98%) than pure chitosan (> 15.2%) against aphid species. N-(3-phenyl butyl) chitosan and N-(ethyl butyl) chitosan were the most and least active derivatives. Results confirmed that the chemical modification of chitosan increased the aphicidal activity. A comparison of the aphicidal activities confirmed that N-alkyl derivatives of commercial chitosan had more toxic effects on aphid species than derivatives of grasshopper chitosan. No significant differences were observed between the two groups of commercial and C. trachypterus chitosan derivatives. This encourages us to introduce N-alkyl derivatives of grasshopper chitosan as a promising alternative source of aphicides in future. [ABSTRACT FROM AUTHOR]

The development time, survivorship and reproduction of the Sarucallis kahawaluokalani (Kirkaldy), Eucallipterus tiliae L., Capitophorus elaeagni del Guercio, Aphis nerii Boyer de Fonscolombe, Cinara cedri Mimeur were studied on the Lagerstroemia indica L., Tilia tomentosa Moench, Elaeagnus angustifolia L., Nerium oleander L. and Cedrus libani Loud. at four constant temperatures (20C, 22.5C, 25C and 27.5C). Total nymphal development time ranged from 7.78 d at 22.5C to 9.81 d at 25C of C.elaeagni, 9.32 d at 25C to 12.5 d at 20C of E. tiliae, 7.08 d at 27,5C to 11.14 d at 20C of S. kahawaluokalani, 15.85 d at 25C to 12.57 d at 20C of A. nerii and 13.00 d at 20C to 10.07 d at 25C of C. cedri. The intrinsic rate of increase (rm) at 22.5C had the highest value for S. kahawaluokalani and C. elaeagni (0.5703) and (0.2945) among all tested constant temperatures. The calculated rm was higher at 25C for E. tiliae (1.4124) and C. cedri (0.2975) and at 20C A. nerii (0.2648). That the optimal temperature for E. tiliae and C.cedri on T. tomentosa and C. libani was 25C, for C. elaeagni and E. tiliae was 22.5C on E. angustifolia and T. tomentosa and for A. nerii was 20C on N. oleander.

Trophic cascades occur when predators benefit plants by consuming herbivores, but the overall strength of a trophic cascade depends upon the way species interactions propagate through a system. For example, plant resistance to, or tolerance of, herbivores reduces the potential magnitude of a trophic cascade. At the same time, plants can also affect predator foraging or consumption in ways that either increase or decrease the strength of trophic cascades. In this study, we investigated the effects of plant variation on cascade strength by manipulating predator access to aphid populations on two species of milkweed: the slower-growing, putatively more-defended Asclepias syriaca and the faster-growing, putatively less-defended Asclepias incarnata. Predatory insects increased plant growth and survival for both species, but the strength of these trophic cascades was greater on A. incarnata, which supported more aphid growth early in the season than did A. syriaca. More predators were observed per aphid on A. incarnata, and cage treatments generated significant patterns consistent with predator aggregation on A. incarnata, but not A. syriaca. Although predators strongly affected aphids, this effect did not differ consistently between milkweed species. Plant tolerance to herbivory may therefore be the primary driver of the difference in trophic cascade strength observed. Importantly, we observed that the timing of predator exclusion affected plant growth and survival differently, indicating that measures of 'cascade strength' may change with phenology and plant physiological responses. Together, our results suggest a mechanism by which differences in resource allocation patterns could explain differences in growth, phenology, and cascade strength between species. [ABSTRACT FROM AUTHOR]

The aim of this work was to examine, both in the field and in the laboratory, ecological aspects of selected plant-aphid-parasitoid interactions to evaluate their potential for the open rearing of the parasitoid Lysiphlebus testaceipes (Cresson) (Hymenoptera: Aphidiinae) for the control of Aphis craccivora (Koch) (Hemiptera: Aphididae) in alfalfa agroecosystems. To this end quantitative samplings of parasitoids and aphids were made fortnightly in three alfalfa crop fields and their spontaneously vegetated edges, in Rafaela (Santa Fe, Argentina), during three years (2009-2011). Three sink webs based on L. testaceipes, on a per-year basis, were constructed to assess the strength of the interactions established by aphids and parasitoids, the host ranges of alternative aphid species, and the tendencies in parasitoid host use across years. In the laboratory, emergence rates, parasitism rates, larval and pupal development times, and adult lifespan of L. testaceipes were analyzed by means of choice tests, including the alternative and the target aphid species in the assays. About 84 % of adults of L. testaceipes obtained in the samples came from Aphis nerii (Boyer de Fonscolombe), an innocuous aphid species only associated with plants of the genus Araujia Brotero (Apocynaceae). Based on our results, the system proposed has many features that support its feasibility to be used as an open rearing system of L. testaceipes: unrisky alternative aphid, easy reproduction of the banker plant and similar suitability of innocuous and pest aphid species for the parasitoid to oviposit and complete their development without noticeably preference for specific hosts. [ABSTRACT FROM AUTHOR]

The insecticidal activity of four natural products based on soaps prepared from plant oils (sunflower and olive) against Aphis nerii Boyer de Fonscolombe and Macrosiphum rosae (L.) was evaluated in vitro. It was found that SLGEL1521OLT, SLUN and OLGEL manifested the strongest insecticidal activity against both aphids. A higher efficacy was observed towards M. rosae, as compared with A. nerii. The number of surviving individuals was recorded after 24h. The efficacy was estimated by means of the Henderson and Tilton formula (1955) and the results were statistically analyzed with the R language for statistical computing (R Development Core Team, 2011) and the drc R language package. [ABSTRACT FROM AUTHOR]

The diversity of vectors and fleeting nature of virus acquisition and transmission renders nonpersistent viruses a challenge to manage. We assessed the importance of noncolonizing versus colonizing vectors with a 2-yr survey of aphids and nonpersistent viruses on commercial pumpkin farms. We quantified aphid alightment using pan traps, while testing leaf samples with multiplex RT-PCR targeting cucumber mosaic virus (CMV), zucchini yellow mosaic virus (ZYMV), watermelon mosaic virus (WMV), and papaya ringspot virus (PRSV). Overall, we identified 53 aphid species (3,899 individuals), from which the melon aphid, Aphis gossypii Glover, a pumpkin-colonizing species, predominated (76 and 37% of samples in 2010 and 2011, respectively). CMV and ZYMV were not detected, but WMV and PRSV were prevalent, both regionally (WMV: 28/29 fields, PRSV: 21/29 fields) and within fields (infection rates = 69 and 55% for WMV in 2010 and 2011; 28 and 25% for PRSV in 2010 and 2011). However, early-season samples showed extremely low infection levels, suggesting cucurbit viruses are not seed-transmitted and implicating aphid activity as a causal factor driving virus spread. Interestingly, neither noncolonizer and colonizer alightment nor total aphid alightment were good predictors of virus presence, but community analyses revealed species-specific relationships. For example, cowpea aphid (Aphis craccivora Koch) and spotted alfalfa aphid (Therioaphis trifolii Monell f. maculata) were associated with PRSV infection, whereas the oleander aphid (Aphis nerii Bover de Fonscolombe) was associated with WMV spread within fields. These outcomes highlight the need for tailored management plans targeting key vectors of nonpersistent viruses in agricultural systems. [ABSTRACT FROM AUTHOR]

In plant-ant-hemipteran interactions, ants visit plants to consume the honeydew produced by phloem-feeding hemipterans. If genetically based differences in plant phloem chemistry change the chemical composition of hemipteran honeydew, then the plant's genetic constitution could have indirect effects on ants via the hemipterans. If such effects change ant behavior, they could feed back to affect the plant itself. We compared the chemical composition of honeydews produced by Aphis nerii aphid clones on two milkweed congeners, Asclepias curassavica and Asclepias incarnata, and we measured the responses of experimental Linepithema humile ant colonies to these honeydews. The compositions of secondary metabolites, sugars, and amino acids differed significantly in the honeydews from the two plant species. Ant colonies feeding on honeydew derived from A. incarnata recruited in higher numbers to artificial diet, maintained higher queen and worker dry weight, and sustained marginally more workers than ants feeding on honeydew derived from A. curassavica. Ants feeding on honeydew from A. incarnata were also more exploratory in behavioral assays than ants feeding from A. curassavica. Despite performing better when feeding on the A. incarnata honeydew, ant workers marginally preferred honeydew from A. curassavica to honeydew from A. incarnata when given a choice. Our results demonstrate that plant congeners can exert strong indirect effects on ant colonies by means of plant-species-specific differences in aphid honeydew chemistry. Moreover, these effects changed ant behavior and thus could feed back to affect plant performance in the field. [ABSTRACT FROM AUTHOR]

Aphidius colemani Viereck (Hymenoptera: Braconidae) is a pan-tropical broadly oligophagous endoparasitoid of many aphids of economic importance, including Aphis gossypii Glover and Myzus persicae (Sulzer). While the trophic interactions occurring among A. colemani and its hosts have been extensively studied, little is known about the male- and female-borne cues that guide mating dynamics. Male wing fanning has been found to play a key role in A. colemani courtship, as successful mounting of females without initial wing fanning has never been observed. In this research, we analyzed wing fanning performance and mating ability of males from three different strains of A. colemani: wasps commercially mass-reared on A. gossypii, wild wasps from parasitized A. gossypii, and wild wasps from parasitized Aphis nerii Boyer de Fonscolombe. Results showed that virgin females did not rely on particular male fanning features during mate choice. Moreover, when A. colemani individuals developed on A. gossypii, no major differences were detected in courtship and mating ability between field collected and mass-reared wasps. In contrast, courtship performance and mating success varied between wild A. colemani males reared on different hosts, with those developing on A. nerii having lower quality wing fanning performance during the mounting attempt phase, and reduced ability to compete for females with other males reared on A. gossypii. [ABSTRACT FROM AUTHOR]

The oleander aphid, Aphis nerii Boyer de Fonscolombe, feeds on members of the Apocynaceae family, including several Asclepias species and Cynanchum laeve. Milkweeds alongside and within agricultural crops provide opportunities for natural enemies to encounter and feed upon A. nerii. The predator fauna associated with natural populations of A. nerii on four milkweed species was determined. The development and fecundity of two Coccinellidae species, Harmonia axyridis (Pallas) and Cycloneda munda (Say), were investigated in a laboratory. The development of fourth instar Coccinellidae when fed diets containing A. nerii from host plants having a low or high concentration of cardenolides was investigated. Immature beetle survival was generally poor and longevity was not significantly different when fed A. nerii from different host plant species, with similar survival patterns observed for first and fourth instar Coccinellidae larvae. Both H. axyridis and C. munda exhibited a reduced fecundity when fed A. nerii regardless of milkweed host species compared to beetle fecundity when fed a diet of Acyrthosiphon pisum. When provided with mixed diets, larvae consumed significantly more A. pisum than A. nerii. Larvae continued to accept A. nerii even after feeding on the aphid provoked emesis. Observations revealed that a fluid leaked from within wounded aphids temporarily or permanently immobilized lady beetle larvae. The unsuitability of A. nerii for lady beetles and the common association of milkweeds with agroecosystems raises concerns about the possible effects of feeding on this aphid by biological control agents. [ABSTRACT FROM AUTHOR]

Laboratory and semi-field experiments were carried out during 2013 winter season at Sharkia region to evaluate the performance of the parasitoid species Diaeretiella rapae (M'Intosh)for controlling Brevicoryne brassicae L., Aphis craccivora (Koch) and Aphis nerii Boyer infesting cabbage, faba bean and oleander plants. With the increase of parasitoid density, the percentage of parasitism increased to reach a maximum of 35.7, 29.7 and 25.2% for D. rapae at 11 parasitoid/200 aphids per jar in laboratory and a minimum of 11.30, 7.30 and 5.90% at one parasitoid per jar. Meanwhile, the highest percentage of parasitism were 92.20, 83.20 and 79.30% for D. rapae at 20 parasitoids/200aphids per cage in semi-field test, a minimum of 61.80, 48.70 and 41.50% recorded at five parasitoids per cage on B. brassicae, A. craccivora and A. nerii, respectively. On the other hand, with the increase of parasitoid density the percentage of emerged adults decreased to reach a maximum of 80.93, 75.54 and 63.85% for D. rapae at one parasitoid per jar in laboratory and 77.80, 73.56 and 57.90% at five parasitoids per cage in the field on B. brassicae, A. craccivora and A. nerii, respectively. With the increase of parasitoid density the fecundity of the parasitoid D. rapae increased (as number of mummies and emerged adults increased). The maximum numbers of mummies in the field were 185.60, 166.4 and 158.6 for D. rapae at 20 parasitoids per cage and minimum of 124.60, 97.40 and 83.0 mummies at five adults per cage. It is concluded that the parasitoid D. rapae could have the potential to be suitable biological control agent against B. brassicae, A. craccivora and A. nerii. [ABSTRACT FROM AUTHOR]

The development time, survivorship and reproduction of the Sarucallis kahawaluokalani (Kirkaldy), Eucallipterus tiliae L., Capitophorus elaeagni del Guercio, Aphis nerii Boyer de Fonscolombe, Cinara cedri Mimeur were studied on the Lagerstroemia indica L., Tilia tomentosa Moench, Elaeagnus angustifolia L., Nerium oleander L. and Cedrus libani Loud. at four constant temperatures (20°C, 22.5°C, 25°C and 27.5°C). Total nymphal development time ranged from 7.78 d at 22.5°C to 9.81 d at 25°C of C.elaeagni, 9.32 d at 25°C to 12.5 d at 20°C of E. tiliae, 7.08 d at 27,5°C to 11.14 d at 20°C of S. kahawaluokalani, 15.85 d at 25°C to 12.57 d at 20°C of A. nerii and 13.00 d at 20°C to 10.07 d at 25°C of C. cedri. The intrinsic rate of increase (rm) at 22.5°C had the highest value for S. kahawaluokalani and C. elaeagni (0.5703) and (0.2945) among all tested constant temperatures. The calculated rm was higher at 25°C for E. tiliae (1.4124) and C. cedri (0.2975) and at 20°C A. nerii (0.2648). That the optimal temperature for E. tiliae and C.cedri on T. tomentosa and C. libani was 25°C, for C. elaeagni and E. tiliae was 22.5°C on E. angustifolia and T. tomentosa and for A. nerii was 20°C on N. oleander. [ABSTRACT FROM AUTHOR]

The oleander aphid, Aphis nerii Boyer de Fonscolombe, feeds on milkweeds in the Apocynaceae family. In Kentucky, A. nerii colonizes several common Asclepias species and honeyvine milkweed, Cynanchum laeve (Michaux). Previous studies investigating whether and how host plant characteristics influence A. nerii fitness have produced conflicting results. Our observations suggested that A. nerii more readily colonized C. laeve than Asclepias species. We hypothesized that aphid fitness differed among host plant species having different characteristics, and specifically, that A. nerii performance would be greatest on host plants having low cardenolide concentrations and few physical defenses. Physical and chemical characteristics were measured on C. laeve and three Asclepias species. Laboratory and field experiments were conducted to compare A. nerii performance among these four milkweed species in the absence of natural enemies. Changes in aphid densities over time were examined in the presence of natural enemies. Plant characteristics and aphid performance were found to differ among milkweed species. In the absence of natural enemies, A. nerii performance was best on C. laeve. When exposed to natural enemies, A. nerii densities remained higher on A. incarnata and C. laeve than on A. syriaca and A. tuberosa. Physical differences between C. laeve, a vining milkweed, and tested Asclepias species may increase suitability of honeyvine milkweed for A. nerii colonization. Our results suggest that C. laeve may rely more on tolerance and less on nonpreference or antibiosis resistance to herbivores. [ABSTRACT FROM AUTHOR]

To reduce the dependence on the sometimes unwise use of synthetic pesticides in fruit and vegetable plantations, the toxicity and repellence of Peganum harmala L. (Zygophyllaceae) acetonic seed extract was assayed against several insect pests. For contact toxicity, 3- to 4-d-old individuals of Aphisfabae Scopoli, A. gossypii Glover, A. nerii Boyer de Fonscolombe and Myzus persicae (Sulzer) were included, as well as 1- to 7-d-old adult Tribolium castaneum (Herbst). Repellent effect experiments were conducted on adult, 1- to 2- and 3- to 4-d old M. persicae individuals. At 60 mg mL-1, the topical bioassay mortality percentage was significantly higher in A. gossypii than in A.fabae and A. nerii after 12-72 h. Mortality of the treatments on M. persicae was 87.1% and 90.0% after 24 and 48 h, respectively, and significantly higher than A.fabae and A. nerii during this period. At 60 mg mL-1, the mortality of T. castaneum was much lower than that of the aphid species. T highest repellent index (over 72%) was observed on 1- to 2-d-old M. persicae individuals. [ABSTRACT FROM AUTHOR]

1. The body tissues of insect herbivores contain higher concentrations of nitrogen and phosphorus than do their host plants, leading to an elemental mismatch that can limit herbivore growth, fecundity and ultimately influence population dynamics. While low nutrient availability can limit herbivore growth and reproduction, nutrient levels that exceed an organism’s nutritional requirements, i.e. an organisms’ threshold elemental ratio, can also decrease performance. 2. We conducted a laboratory experiment to examine the impacts of nitrogen and phosphorus additions on population growth rates of a phloem-feeding insect herbivore. 3. Herbivore per capita population growth rates were highest at intermediate foliar nitrogen concentrations, indicating a performance cost on the highest nitrogen foliage. While there was no direct effect of foliar phosphorus concentration on insect performance, there was a strong and unexpected indirect effect. High soil phosphorus availability increased both foliar nitrogen concentrations and aphid tissue nitrogen, resulting in low population growth rates when both soil nitrogen and phosphorus availabilities were high. 4. In this study, experimental increases in foliar nitrogen levels led to a decrease in herbivore performance suggesting that excessive nutrient levels can limit herbivore population growth rates. [ABSTRACT FROM AUTHOR]

Abstract: The term ‘idiobiont’ refers to those parasitoid species that permanently paralyse their hosts during parasitism, causing the cessation of host growth and development. This is in contrast to koinobiont parasitoids, which allow their hosts to continue developing after being parasitized. While no koinobiont species induce permanent paralysis in their hosts, a minority of koinobionts induce a temporary paralysis that does not interfere with overall host growth and development. We characterized transient paralysis induction in two koinobiont aphid parasitoids in the genus Binodoxys (Hymenoptera: Aphidiinae). Both Binodoxys species induced transient paralysis in Aphis glycines, with paralysis time ranging between 4.5 and 8min (depending upon parasitoid species and host instar). In a separate experiment, B. communis was capable of inducing transient paralysis in nine aphid species. We addressed two hypotheses potentially explaining the adaptive value of temporary host paralysis in experiments using A. nerii, which is readily accepted but engages in strong defensive behaviour. The first hypothesis is that paralysis increases oviposition success by interfering with host defences and the second is that it aids in the avoidance of self-superparasitism. Paralysed aphids were more likely to be rejected by B. communis than were aphids that had never been stung or that had recovered from paralysis. This result supports the avoidance-of-self-superparasitism hypothesis and is inconsistent with the hypothesis that transient paralysis increases oviposition success of B. communis. [Copyright &y& Elsevier]

Coexistence of host-specific herbivores on plants is believed to be governed by interspecific interactions, but few empirical studies have systematically unraveled these dynamics. We investigated the role of several factors in promoting coexistence among the aphids Aphis nerii, Aphis asciepiadis, and Myzocallis asciepiadis that all specialize on common milkweed (AscIepias syriaca). Competitive exclusion is thought to occur when interspecific competition is stronger than intraspecific competition. Consequently, we investigated whether predators, mutualists, or resource quality affected the strength of intra- vs. interspecific competition among aphids in factorial manipulations of competition with exposure to predation, ants, and variable plant genotypes in three separate expefiments. In the predation X competition experiment, predators reduced aphid per capita growth by 66%, but the strength of intra- and interspecific competition did not depend on predators. In the ants X competition experiment, ants reduced per capita growth of A. nerii and M. asciepiadis (neither of which were mutualists with ants) by approximately one-half. In so doing, ants ameliorated the negative effects of these competitors on ant-tended A. asciepiadis by two-thirds, representing a novel benefit of ant-aphid mutualism. Nevertheless, ants alone did not explain the persistence of competitively inferior A. a.cclepiadis as, even in the presence of ants, interspecific competition remained stronger than intraspecific competition. In the plant genotype X competition experiment, both A. asciepiadis and M. asciepiadis were competitively inferior to A.'nerii, with the strength of interspecific competition exceeding that of intraspecific cOmpetition by 83% and 23%, respectively. Yet these effects differed among milkweed genotypes, and there were one or more plant genotypes for each aphid species where coexistence was predicted. A synthesis of our results shows that predators play little or no role in preferentially suppressing competitively dominant A. nerii. Nonetheless, A. asciepiadis benefits from ants, and A. asciepiadis and M. asciepiadis may escape competitive exclusion by A. nerii on select milkweed genotypes. Taken as a whole, the coexistence of three host-specific aphid species sharing the same resource was promoted by the dual action of ants as antagonists and mutualists and by genetic diversity in the plant population itself. [ABSTRACT FROM AUTHOR]

Habitat selection by dispersers is the focus of much theoretical models, most of which are based on the assumption of negative density dependence. The archetype of these models is the ideal free distribution, characterized by an evolutionary stable state where more competitors aggregate in better habitats, so that the fitness benefit of resource abundance is equally offset by the cost of competition in all habitats. In this study, we used parentage analysis on microsatellite genotypes to test the ideal free distribution in a natural population of aphid parasitoids. Parentage analysis was conducted on parasitoids emerging from aphid colonies. We inferred the number of foundress females which had reproduced in each colony, as well as the number of offspring for each foundress. As predicted by the ideal free distribution, the number of offspring per foundress per colony did not depend on the number of hosts per colony. However, contrary to ideal free distribution predictions, it was affected by the number of foundresses per colony. In surprising contrast with the basic assumption of negative density dependence, individual fitness increased with the number of foundresses. Moreover, parentage analysis revealed a very low number of offspring per foundress per colony (mean = 1.8). This observed distribution questions the validity of classical models of habitat choice based on competition. Indeed, our results provide a new illustration reinforcing a growing body of theory and data on positive density dependence. Our results also suggest that the avoidance of hyperparasitism and predation, although generally neglected, may shape the distribution of parasitoids in the field. [ABSTRACT FROM AUTHOR]

1. Anthropogenic increases in nitrogen deposition are impacting terrestrial ecosystems worldwide. While some of the direct ecosystem-level effects of nitrogen deposition are understood, the effects of nitrogen deposition on plant–insect interactions and on herbivore population dynamics have received less attention. 2. Nitrogen deposition will potentially influence both plant resource availability and herbivore population growth. If increases in herbivore population growth outstrip increases in resource availability, then increases in the strength of density dependence expressed within the herbivore population would be predicted. Alternatively, if plant resources respond more vigorously to nitrogen deposition than do herbivore populations, a decline in the strength of density dependence would be expected. No change in the strength of density dependence acting upon the herbivore population would suggest equivalent responses by herbivores and plants. 3. A density manipulation experiment was performed to examine the effect of nitrogen deposition on the interaction between a host plant, Asclepias tuberosa, and its herbivore, Aphis nerii. Aphid maximum per capita growth rate ( Rmax), carrying capacity ( K), and the strength of density dependence were measured under three nitrogen deposition treatments. The effect of nitrogen deposition on the relationship among these three measures of insect population dynamics was explored. 4. Simulated nitrogen deposition increased aphid per capita population growth, plant foliar nitrogen concentrations, and plant biomass. Nitrogen deposition caused Rmax and K to increase proportionally, leading to no overall change in the strength of density dependence. In this system, potential changes in the negative feedback processes operating on herbivore populations following nitrogen deposition appear to be buffered by concomitant changes in resource availability. [ABSTRACT FROM AUTHOR]

Abstract: The effects of different prey species on preimaginal development and survival, as well as on adult longevity and fecundity of the predatory lacewing Dichochrysa prasina Burmeister were studied under laboratory conditions. The prey species tested were the aphids Aphis fabae Scopoli, Aphis nerii Boyer de Fonscolombe, Aphis pomi De Geer, Hyalopterous pruni Geoffroy, Macrosiphum rosae (L.) and Myzus persicae (Sulzer), the “two spotted spider mite”Tetranychus urticae Koch, the “moth”Ephestia kuehniella (Zeller) and the “beetles”Tribolium confusum Duval and Tenebrio molitor (L.). Eggs of E. kuehniella and nymphs of M. persicae were the most favorable among the tested prey, resulting in high survival and short developmental time of preimaginal stages as well as in increased adult longevity and fecundity of D. prasina. Larvae of T. molitor were less favorable, resulting in a decrease of adult longevity and fecundity of D. prasina. Among the other prey studied, nymphs of A. fabae, A. pomi, H. pruni and M. rosae, nymphs and adults of T. urticae, and larvae of T. confusum were the least favorable for development, whereas nymphs of A. nerii did not allow the completion of larval development of D. prasina. These results could be useful for mass-rearing of D. prasina and for understanding its population dynamics in the field in relation to the availability of certain prey species. [Copyright &y& Elsevier]

Maternal effects have the potential to affect population dynamics and evolution. To affect population dynamics, maternal effects must influence offspring vital rates (birth, death, or movement). Here, we explore the magnitude of nongenetic maternal influence on the vital rates of an insect herbivore and explore predictability of maternal effects with reference to published studies. We experimentally studied the effects of maternal age, host plant species (two Asclepias spp.), and density on offspring vital rates in Aphis nerii, the oleander aphid. Older mothers produced offspring that lived shorter lives, consistent with the ‘Lansing Effect.’ Older mothers also produced offspring that matured at a younger age. As maternal age increased, offspring mass at maturity decreased when mothers were on Asciepias syriaca. However, offspring mass was highest from intermediate aged mothers on A. vividis. The absence of maternal density effects seems to exclude maternal density as a potential source of delayed density dependence in A. nerli. Our results indicate that maternal effects have some influence on A. nerii vital rates. However, references to published studies suggest that only the Lansing Effect is a predictable response to maternal age in insects. Moreover, the magnitude of observed effects was generally low. [ABSTRACT FROM AUTHOR]

1. Non-Mendelian maternal effects, the effects of maternal phenotype or environment on offspring phenotype, have been documented in numerous taxa. By affecting offspring vital rates (birth, death, and movement), maternal effects have the potential to influence population dynamics. However, relatively few studies have directly linked maternal phenotype or environment to offspring vital rates. Additionally, even fewer studies have compared the magnitude of across-generation effects (i.e. maternal effects) to within-generation effects. 2. Because of their telescoping generations, aphids can be strongly influenced by maternal effects. The effects of maternal density and maternal host-plant species on offspring survival, fecundity, and alate formation were investigated experimentally in Aphis nerii, the milkweed–oleander aphid. 3. Additionally, the relative strength of maternal effects were compared with those operating within a generation. Therefore, in another set of experiments, the effects of current density and host-plant species (within-generation effects) on aphid vital rates were examined. 4. While maternal effects were present, within-generation effects were much stronger and more strongly influenced aphid vital rates. Within a generation, aphids exhibited density-dependent survival, fecundity, and alate formation and these effects varied among host-plant species. 5. These results indicate that while maternal effects have the potential to affect population dynamics, this potential is not always met. Additionally, the current environment, not the environment of previous generations, more strongly impacts population dynamics. [ABSTRACT FROM AUTHOR]

An invasive, exotic coccinellid, Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae), was recently identified as a potential hazard to immature monarch butterflies, Danaus plexippus L. (Lepidoptera: Nymphalidae). To further evaluate the risk of H, axyridis impacting D. plexilous, we evaluated the influence of an alternate prey, Aphis nerii Boyer de Fonscolombe (Homoptera: Aphididae), on the predation rate of H. axyridis on D. plexippus larvae. When first-instar D, plexippus were placed in petri dish arenas with third-instar H. axyridis and varying densities of A, nerii, D. plexippus survival after 24 h increased significantly from 0% with 0 A. nerii present to 73% with 30 A. nerii present. In predation studies conducted in field cages, survival of D. plexippus larvae decreased with increasing densities of H. axyridis larvae and tended to increase with increasing A, nerii densities. These studies indicate that H. axyridis will feed on D. plexippus larvae in the presence of A. net/i, but that the presence of A. nerii lessens the severity of predation on D. plexippus. [ABSTRACT FROM AUTHOR]

1. Experimental evidence is presented for positive, negative, and no density dependence from 32 independent density manipulations of milkweed aphids (Aphis nerii) in laboratory and field experiments. This substantial variation in intraspecific density dependence is associated with temperature and host-plant species.2. It is reported that as population growth rate increases, density dependence becomes more strongly negative, suggesting that the monotonic definition of density dependence used in many common population models is appropriate for these aphids, and that population growth rate and carrying capacity are not directly proportional.3. For populations that conform to these assumptions, population growth rate may be widely applicable as a predictor of the strength of density dependence. [ABSTRACT FROM AUTHOR]

Long-standing theory has predicted that plant defensive and nutritional traits contribute to the population dynamics of insect herbivores. To examine the role of plant variation in density dependence, I took a comparative approach by conducting density manipulation experiments with the specialist aphid, Aphis nerii, on 18 species of milkweed (Asclepias spp.). The strength of density dependence varied on the plant species. Variation in plant secondary compounds (cardenolides), trichomes, leaf carbon and nitrogen concentrations, and seed mass of the milkweed species predicted the Rmax of aphid populations, while specific leaf weight, carbon concentration, latex, water content, and trichome density were significant predictors of the strength of density dependence. Thus, plant traits that probably evolved for primary and defensive functions contribute to the ecological dynamics of herbivore populations. [ABSTRACT FROM AUTHOR]

The effect of aphid population size on host-plant chemical defense expression and the effect of plant defense on aphid population dynamics were investigated in a milkweed-specialist herbivore system. Density effects of the aposematic oleander aphid, Aphis nerii, on cardenolide expression were measured in two milkweed species, Asclepias curassavica and A. incarnata. These plants vary in constitutive chemical investment with high mean cardenolide concentration in A. curassavica and low to zero in A. incarnata. The second objective was to determine whether cardenolide expression in these two host plants impacts mean A. nerii colony biomass (mg) and density. Cardenolide concentration (µg/g) of A. curassavica in both aphid-treated leaves and opposite, herbivore-free leaves decreased initially in comparison with aphid-free controls, and then increased significantly with A. nerii density. Thus, A. curassavica responds to aphid herbivory initially with density-dependent phytochemical reduction, followed by induction of cardenolides to concentrations above aphid-free controls. In addition, mean cardenolide concentration of aphid-treated leaves was significantly higher than that of opposite, herbivore-free leaves. Therefore, A. curassavica induction is strongest in herbivore-damaged tissue. Conversely, A. incarnata exhibited no such chemical response to aphid herbivory. Furthermore, neither host plant responded chemically to herbivore feeding duration time (days) or to the interaction between herbivore initial density and feeding duration time. There were also no significant differences in mean colony biomass or population density of A. nerii reared on high cardenolide (A. curassavica) and low cardenolide (A. incarnata) hosts. [ABSTRACT FROM AUTHOR]

1. Previous studies have demonstrated that phenotypic traits of plants have the potential to affect interactions between herbivores and their natural enemies. Consequently, the impact of natural enemies on herbivore vital rates and population dynamics may vary among plant species. This study was designed to investigate the potential for density-dependent parasitism of an aphid herbivore feeding on six different host plant species. 2. Population densities of the aphid Aphis nerii B de F (Homoptera: Aphididae) and its parasitoid Lysiphlebus testaceipes Cresson (Hymenoptera: Braconidae) were recorded within a single growing season on six different species of milkweed in the genus Asclepias L. (Asclepiadaceae). Asclepias species are known to vary in their quality as food for herbivores. Although data on plant quality were not available in this study, population data were analysed to determine the effects of different Asclepias species on rates of parasitism and aphid population growth. 3. Parasitism rates of A. nerii varied among Asclepias species but were temporally density dependent over at least some range of aphid density on all plant species. Aphid population growth rates also varied among Asclepias species, and declined with an increase in the maximum parasitism rates among plant species; however, in no case was density-dependent parasitism sufficient to prevent exponential population growth of aphids within the growing season. The results serve to emphasise that, if natural enemies are to regulate herbivore populations, density-dependent mortality is a necessary, but not sufficient, condition for regulation. [ABSTRACT FROM AUTHOR]

Oleander aphids, ( Aphis nerii), which are sporadically tended by ants, were used as a moded system to examine whether host plant factors associated with feeding site influenced the formation of ant-aphid associations. Seasonal patterns of host plant utilization and association with attendant ants were examined through bi-weekly censuses of the aphid population feeding on thirty ornamental oleander plands ( Nerium oleander) in northern California in 1985 and 1986. Colonies occurred on both developing and senescing plant terminals, including leaf tips, floral structures, and pods. Aphids preferentially colonized leaf terminals early in the season, but showed no preference for feeding site during later periods. Argentine ants ( Iridomyrmex humilis) occasionally tended aphid colonies. Colonies on floral tips were three to four times more likely to attract ants than colonies on leaf tips, even though the latter frequently contained more aphids. Ants showed a positive recruitment response to colonies on floral tips, with a significant correlation between colony size and number of ants. There was no recruitment response to colonies on leaf tips. These patterns were reproducible over two years despite large fluctuations in both aphid population density and ant activity. In a laboratory bioassay of aphid palatability, the generalist predator, Hippodamia convergens, took significantly more aphids reared on floral tips compared to those reared on leaf tips. The patterns reported here support the hypothesis that tritrophic factors may be important in modifying higher level arthropod mutualisms. [ABSTRACT FROM AUTHOR]

The use of chemical insecticides has had several side-effects, such as environmental contamination, foodborne residues, and human health threats. The utilization of plant-derived essential oils as efficient bio-rational agents has been acknowledged in pest management strategies. In the present study, the fumigant toxicity of essential oil isolated from Satureja intermedia was assessed against cosmopolitan stored-product insect pests: Trogoderma granarium Everts (khapra beetle), Rhyzopertha dominica (Fabricius) (lesser grain borer), Tribolium castaneum (Herbst) (red flour beetle), and Oryzaephilus surinamensis (L.) (saw-toothed grain beetle). The essential oil had significant fumigant toxicity against tested insects, which positively depended on essential oil concentrations and the exposure times. Comparative contact toxicity of S. intermedia essential oil was measured against Aphis nerii Boyer de Fonscolombe (oleander aphid) and its predator Coccinella septempunctata L. (seven-spot ladybird). Adult females of A. nerii were more susceptible to the contact toxicity than the C. septempunctata adults. The dominant compounds in the essential oil of S. intermedia were thymol (48.1%), carvacrol (11.8%), p-cymene (8.1%), and γ-terpinene (8.1%). The high fumigant toxicity against four major stored-product insect pests, the significant aphidicidal effect on A. nerii, and relative safety to the general predator C. septempunctata make terpene-rich S. intermedia essential oil a potential candidate for use as a plant-based alternative to the detrimental synthetic insecticides. [ABSTRACT FROM AUTHOR]