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Resistance to insecticides used to control pests is an issue of increasing concern for agriculture. The grain aphid, Sitobion avenae, is a pest of cereals and grasses worldwide, and one of growing concern due to the evolution of resistance to certain insecticides. Resistance confers benefits to insects by enabling them to survive exposure to insecticide compounds; however, the mutations conferring resistance may also penalise the insect in pesticide-free environments due to fitness costs associated with the new phenotype. Here we tested the hypothesis of a reproductive penalty linked to the knockdown resistance mutation (kdr) to pyrethroid insecticides. The mutation occurs predominantly in a single SA3 clone. To date, only heterozygous-resistant forms (kdr-SR) have been detected in populations in Ireland and the UK, and this suggests that a fitness penalty may preclude the formation of both male and female heterozygous-resistant sexual forms. By designing an experiment which included a resistant and a non-resistant clone, we were able to simulate reduced daylight and temperature conditions which, in nature, trigger sexual reproduction and therefore study the responses of each clone. This allowed us to detect the switch from asexual females to sexual females and males and report on the conditions associated with the production of sexual forms. The results showed that both aphid clones were able to produce sexual forms with no difference in the onset of sexual reproduction, although reproductive strategies differed between clones. The later onset of male forms in the SA3 clone may decrease the likelihood of mating interactions to create fully resistant (kdr-RR) genotypes and this may constitute a fitness penalty due to pyrethroid resistance.

Most species of moths use a female-produced sex pheromone to bring mates together. Typically, sex pheromone is synthesized in a specialized gland and released during the behavior of "calling", in which the ovipositor and gland are extruded, allowing pheromone to evaporate. Although there has been much study on how a gland makes specific pheromone components, we know relatively little about how it actually functions with regard to synthesis, storage and release. In this paper, we investigated three aspects of gland function in the noctuid moth Chloridea virescens (Fabricius): (i) whether translocation of pheromone from site of synthesis to release is dependent on calling or ovipositor movement, (ii) whether pheromone synthesis rate limits release and (iii) how intermittent calling (observed in this and other species) might affect the dynamics of release rate. Firstly, by manipulating the gland to simulate calling (extruded) or non-calling (retracted), we showed that pheromone translocation occurred regardless of whether the gland was retracted or extruded. Secondly, by manipulating pheromone production, we found that females that produced more pheromone had higher release rates. It was especially noticeable that females had a higher release rate at the start of calling, which dropped rapidly and leveled off over time. Together, these data suggest that intermittent calling in C. virescens (and other species) may function to allow females to replenish pheromone stores on the gland surface between calling bouts, so that brief, high release rates occur at the start of a calling bout; thus, potentially increasing a female's chances of attracting a mate.

Results of dose response bioassays 'in vivo' used to characterise the phenotypic response of pyrethroid resistant S. avenae in comparison to susceptible S. avenae, and two other cereal aphids, the rose-grain aphid (Metopholophium dirhodum) and the bird-cherry – oat aphid (Rhopalosiphum padi), are used to measure levels of pyrethroid resistance. Aphid pests on cereals in the British Isles are predominantly controlled by pyrethroid insecticides, especially since the implementation of the recent ban on neonicotinoid seed treatments on all outdoor crops. Resistance to pyrethroids has been detected in one of the main aphid pests, the grain aphid (Sitobion avenae), probably brought on by the sustained use of these pyrethroid sprays to control cereal aphids, which can transmit plant viruses, especially Barley Yellow Dwarf Virus (BYDV). The withdrawal of several insecticide compounds (e.g. pirimicarb, dimethoate, chlorpyrifos and the aforesaid neonicotinoids) for cereal aphid control will probably increase the selection pressure, leading to increased levels of resistance in S. avenae, and, potentially, the evolution of resistance in other cereal aphid species. In this article we present the results of dose response bioassays 'in vivo' used to characterise the phenotypic response of pyrethroid resistant S. avenae in comparison to susceptible S. avenae, and two other cereal aphids, the rosegrain aphid (Metopholophium dirhodum) and the bird-cherry– oat aphid (Rhopalosiphum padi), in order to measure levels of pyrethroid resistance. At present, little is known about the extent of pyrethroid resistance in S. avenae beyond the UK and in other cereal aphids. It therefore becomes increasingly important to monitor these pests to inform crop management decisions in light of the recent loss of other insecticides. The unintended consequences of the rapid withdrawal of insecticides, together with a failure to prepare and install alternative products and control approaches in advance, will probably ultimately lead to the loss of effectiveness of insecticidal compounds like pyrethroids.

Many species of moths have a common control mechanism for synthesizing sex pheromone: the circadian release of pheromone biosynthesis-activation neuropeptide (PBAN) that switches pheromone synthesis on/off during the day. One apparent exception to this is the noctuid moth Trichoplusia ni (Hubner), in which pheromone synthesis appears continuous through the photoperiod, with circadian release of PBAN controlling emission rate of pheromone during calling. Sex pheromone biosynthesis was reinvestigated in T. ni using stable isotope tracer-tracee and gland sampling techniques to ascertain how pheromone quantities in gland cells and on the gland cuticular surface varied and were controlled. It was found that (i) carbohydrate from adult female feeding is used to synthesize sex pheromone, (ii) most of the stored acetate ester pheromone component(s) is contained in gland cells, (iii) a large pool of pheromone is synthesized and stored through the photoperiod with a slow turnover rate, (iv) although pheromone is synthesized throughout the photoperiod, its rate can vary, influenced by release of PBAN and possibly by an unidentified head factor, with both affecting carbohydrate uptake into the acetyl CoA pheromone precursor pool, and (v) as suggested previously, PBAN also influences translocation of pheromone out of the cell to the cuticular surface, possibly by causing breakdown of intracellular lipid droplets storing pheromone molecules. This work suggests that the quantitative synthesis and emission of pheromone in T. ni, and possibly other moths, is regulated by multiple complementary biochemical mechanisms.

The grain aphidSitobion avenaeis a prolific pest of cereal crops worldwide, controlled effectively with pyrethroid insecticides. However, the classic knock down resistance (kdr) mutation, L1014F on theS. avenaesodium channel gene, has been identified as the cause of the recently observed heterozygous (kdr-SR) resistance in the SA3 grain aphid super-clone. Results indicate that the kdr-SR SA3 clone can survive pyrethroid exposure above twice the normal field rate, continuing to reproduce thereafter. Additionally, the SA3 clone was found to be capable of producing sexual oviparous morphs, able to lay eggs following pyrethroid exposure. This demonstrates that possession of the L1014F mutation does not preclude the capacity to produce sexual morphs. This makes the adoption of an effective resistance management strategy imperative, within a wider integrated pest management (IPM) approach to control grain aphid.

Aldehydes are components of many moth sex pheromones, and are thought to be produced from analogous alcohols by oxidase(s) in the cell membrane or the gland cuticle. This implies that the two types of components are produced and/or stored in different parts of the gland: alcohols in cells and aldehydes in cuticle. Few studies have investigated the distribution of components in moth pheromone glands. Using rinse/extract sampling, stable isotope tracer/tracee methods, and decapitation/ pheromone biosynthesis activating neuropeptide stimulation, we studied production and distribution of (Z)-11-hexadecenal (Z11-16:Ald) and (Z)-hexadecenol (Z11-16:OH) in the gland of Chloridea virescens (formerly Heliothis virescens). The rinse, which likely sampled the surface and outer cuticle, contained large amounts of aldehyde and small amounts of alcohol. By contrast, the residual extract, which likely sampled cells and less solvent-accessible (inner) cuticle, had large amounts of alcohol and small amounts of aldehyde. When a tracer (U-13C-glucose) was fed to females, the aldehyde had higher isotopic enrichment than the alcohol in the rinse, but not in the residual extract, showing that in the rinse pool, Z11-16:Ald was, on average, synthesized before Z11-16:OH. This is consistent with greater aldehyde than alcohol flux through the cuticle. While our results are consistent with cell/cuticle synthesis sites for alcohol/aldehyde components, we cannot rule out both being synthesized in gland cells. We propose two alternative conceptual models for how site of production, cuticular transport and catabolism/metabolism might explain the relative masses of Z11-16:Ald and Z11-16:OH translocated to the pheromone gland surface in female C. virescens.

The cabbage stem flea beetle, Psylliodes chrysocephala L. is a major pest of winter oilseed rape in several European countries. Traditionally, neonicotinoid and pyrethroid insecticides have been widely used for control of P. chrysocephala, but in recent years, following the withdrawal of neonicotinoid insecticide seed treatments, control failures have occurred due to an over reliance on pyrethroids. In line with previous surveys, UK populations of P. chrysocephala were found to exhibit high levels of resistance to the pyrethroid lambda-cyhalothrin. This resistance was suppressed by pre-treatment with the cytochrome P450 inhibitor PBO under laboratory conditions, suggesting that the resistance has a strong metabolic component. The L1014F (kdr) mutation in the voltage-gated sodium channel, which confers relatively low levels (10–20 fold) of resistance to pyrethroids, was also found to be widespread across the UK regions sampled, whereas the L925I (s-kdr) mutation was much less common. The current survey also suggests that higher levels of pyrethroid resistance have spread to the North and West of England, and that resistance levels continue to remain high in the South East., Highlights • UK populations of cabbage stem flea beetle exhibit high levels of resistance to pyrethroid insecticides. • Pyrethroid resistance in UK populations is largely the result of increased metabolism. • Resistance has advanced to the North and West of England. • Resistance levels are highest in Yorkshire and the Humber and the South East of the UK.

This is the post-print version of the following article: "Calling Behavior and Sex Pheromone Release and Storage in the Moth Chloridea virescens", which has been published in final form at https://link.springer.com/article/10.1007/s10886-019-01133-w#auth-1; International audience; Female moths release sex pheromone to attract mates. In most species, sex pheromone is produced in, and released from, a specific gland. In a previous study, we used empirical data and compartmental modeling to account for the major pheromone gland processes of female Chloridea virescens: synthesis, storage, catabolism and release; we found that females released little (20–30%) of their pheromone, with most catabolized. The recent publication of a new pheromone collection method led us to reinvestigate pheromone release and catabolism in C. virescens on the basis that our original study might have underestimated release rate (thereby overestimating catabolism) due to methodology and females not calling (releasing) continuously. Further we wished to compare pheromone storage/catabolism between calling and non-calling females. First, we observed calling intermittency of females. Then, using decapitated females, we used the new collection method, along with compartmental modeling, gland sampling and stable isotope labeling, to determine differences in pheromone release, catabolism and storage between (forced) simulated calling and non-calling females. We found, (i) intact 1 d females call intermittently; (ii) pheromone is released at a higher rate than previously determined, with simulations estimating that continuously calling females release ca. 70% of their pheromone (only 30% catabolized); (iii) extension (calling)/retraction of the ovipositor is a highly effective “on/off’ mechanism for release; (iv) both calling and non-calling females store most pheromone on or near the gland surface, but calling females catabolize less pheromone; (v) females are capable of producing and releasing pheromone very rapidly. Thus, not only is the moth pheromone gland efficient, in terms of the proportion of pheromone released Vs. catabolized, but it is highly effective at shutting on/off a high flux of pheromone for release.

International audience; Adult feeding on hosts is common among parasitic wasps. The ingested host fluid is rich in nutrients, especially proteins. A study on Eupelmus vuilleti (Hymenoptera: Eupelmidae), a host-feeding parasitoid of larvae of Callosobruchus maculatus (F.) (Coleoptera: Bruchidae), showed that the carbohydrates (maybe lipids) but not proteins, gained from host feeding accounted for the increased egg production. Thus, host protein is probably utilized for general adult metabolism, allowing conservation of carbohydrate and/or lipid resources for direct allocation to oocytes. In that case, there should be increased N excretion by female parasitoids. To test this, we studied the dynamics of excretion in E. vuilleti with and without host exposure. The aim of this work was threefold: (i) to identify the major N-containing compounds in adult excreta, (ii) to assess whether protein consumption during host feeding increased the amount of N excreted, and (iii), if so, to compare the increase in N excreted with the amount taken in during a single host feeding. We found that uric acid is the predominant N-containing metabolite in excreta, although small quantities of urea and traces of allantoin were also found. A calculation of the N budget showed that the extra quantity of N excreted following a host meal corresponds to the quantity ingested, confirming that host-feeding in this species offers little or no net quantitative benefit in N allocation to oocytes, although the allocation of specific amino acids from host feeding cannot be discounted. Interestingly, host-feeding in parasitoids appears analogous to vertebrate blood-feeding in mosquitoes, both in terms of the N-containing compounds excreted and the offset of acquired N to metabolism, rather than to oo-cytes. Further comparative and detailed investigations of N excretion in insects living on other N-rich fluids might establish further metabolic commonalities.

1. Insecticide usage selects strongly for resistance in aphid populations, but this could entail fitness costs in other resistance traits. The potato aphid Macrosiphum euphorbiae Thomas exhibits intraspecific variation in susceptibility to parasitism by braconid wasps and provides a suitable species to study the relation between the defensive traits of parasitism and insecticide resistance. 2. Clonal lines (23 in total) of M. euphorbiae were established from aphids collected in 2013 from geographically separate populations in the U.K. Clonal lines belonged to five aphid genotypes, but one genotype predominated (78% of samples), and the facultative endosymbiont Hamiltonella defensa was detected in c. 40% of lines. 3. Total esterase activity in aphid tissues varied significantly between aphid genotypes and collection areas, but there was no clear pattern in relation to H. defensa infection or between collection sites likely to differ in insecticide pressures. 4. Five clonal lines representing low to moderate levels of enzyme activity, which included different aphid genotypes and presence/absence of H. defensa infection, were assayed for their susceptibility to the parasitoid wasp Aphidius ervi Haliday. Aphid mummification varied significantly between aphid genotypes, with low values in one genotype of aphids irrespective of H. defensa presence. 5. The results revealed that aphid lines belonging to the parasitism-resistant genotype exhibited moderate levels of total esterase activity, indicating a competitve advantage for this genotype of M. euphorbiae when exposed to chemical and biological control factors in agroecosystems.

By differentially sampling the pheromone gland of females of the moth Heliothis virescens, we explored differences in pheromone on the surface, or outer distal layer(s) of the gland, and that located more proximally. For this, we used two sampling approaches, (i) a solid phase microextraction fiber rub followed by solvent extraction of residual pheromone (SPME rub/extract), and (ii) rapid solvent rinsing followed by solvent extraction of residual pheromone (rinse/extract). The SPME rub showed differences in component ratio between the dorsal and ventral gland surfaces. The rinse sampled a greater amount of pheromone than the SPME rub, sampling the whole gland surface as well as likely deeper into the gland. Compared to the other samplings, pheromone in the rinse was depleted in the minor component; consequently, the corresponding residual extract was highly enriched in the minor component. Further rinses of the gland yielded only small amounts of pheromone, with a similar component ratio as the first rinse, suggesting that the residual pheromone was less accessible and required extraction in solvent to be liberated. Sampling over the photoperiod showed that the more volatile minor component was depleted (relative to the major component) on the surface/outer cuticle over the period when females called. Together, these data suggest that the pheromone is stored, at least in part, on and in the gland cuticle and that distinct pools may be transported to different topographic regions. Females fed with a stable isotope tracer, incorporated label into pheromone in the gland very rapidly, with the labeled pheromone appearing on the gland surface ca. 1 min later.

The plant mirid bugs, Lygus pratensis Linnaeus and Polymerus cognatus Fieber, are key pests on economically important cotton crops and ecologically important grassland in northwestern China. Lambda-cyhalothrin is frequently used against mirid bugs in the regions. In this study, we examined the sublethal and transgenerational effects of short-term exposure to lambda-cyhalothrin on biological traits using a miminal dose, LD5 [0.484 ng/L. pratensis adult, and 0.171 ng/P. cognatus adult], a low lethal dose, LD25 [1.353 ng/L. pratensis adult, and 0.781 ng/P. cognatus adult] and a moderate lethal dose, LD50 [2.766 ng/L. pratensis adult, and 2.243 ng/P. cognatus adult]. Direct exposure to LD50 of lambda-cyhalothrin led to decreased adult longevity, shorter female oviposition period and lower fecundity of the parental generation for both species, whereas treatment with LD5 lambda-cyhalothrin stimulated female fecundity on L. pratensis, but not on P. cognatus. The F1 generation underwent transgenerational effects, i.e. there was delayed egg-laying period and larval development and decreased hatchability for both species, decreased adult longevity and fecundity for L. pratensis, and shortened adult longevity for the LD50 group of P. cognatus. Compared with the untreated control group, the net reproductive rate (R0), the intrinsic rate of increase (rm), and finite rate of increase (λ) were significantly decreased for the groups treated with different doses of lambda-cyhalothrin, whereas the generation time (T) was increased. Our results demonstrate that sublethal effects of lambda-cyhalothrin can retard development and suppress population growth for both of these mirid species. Therefore, this insecticide can be used effectively against mirid bugs in northern China and its application strategy to control mirid bug is discussed.

Moth pheromone research has pioneered much of our understanding of long-distance chemical communication. Two important characteristics of this communication have, however, remained largely unaddressed: the release of small quantities of pheromone by most moth species, despite potential advantages of releasing greater amounts, and the intermittency of release in some species, limiting the time of mate attraction. We addressed the proximate mechanisms underlying these characteristics by manipulating biosynthesis, storage and release of pheromone in females of the noctuid mothChloridea virescens. We found that (i) mass release is determined by pheromone mass on the gland surface; (ii) amounts synthesized are limited by pheromone biosynthesis activating neuropeptide concentration, not precursor availability; (iii) some gland structural feature limits mass release rate; (iv) intermittent calling enables release at a mass rate greater than biosynthetic rate; and (v) at typical mass release rates, the periodicity of pheromone availability on the gland surface roughly matches the periodicity (intermittency) of calling. We conclude that mass release inC.virescensand possibly many other species is low because of constraints on biosynthesis, storage and gland structure. Further, it appears the behaviour of intermittent calling in C.virescensmay have evolved as a co-adaptation with pheromone availability, allowing females to release pheromone intermittently at higher mass rates than the biosynthesis rate.

When attacked by natural enemies some insect pests, including many aphid species, alert neighboring conspecifics with alarm pheromones. Cornicle secretions with pheromones benefit the attacked aphid but are costly to produce, while alarm pheromone benefits probably fall largely on alerted conspecifics. Given these variable benefits, the likelihood of a secretion may change depending on aphid density. Thus, we first hypothesized that the common alarm pheromone in aphids, E-s-farnesene (EBF), was present in soybean aphid (Aphis glycines Matsumura) cornicle secretions and would elicit an alarm response in aphids exposed to it. Second, since aphids other than the secretor also benefit from cornicle secretions, we hypothesized that the likelihood of secretion would increase concurrently with the density of neighboring clonal conspecifics. Third, because alarm reaction behavior (e.g. feeding cessation) is probably costly, we hypothesized that alarm reaction behavior would decrease as conspecific density (i.e. alternative prey for an attacking natural enemy) increased. We found that soybean aphids 1) produce cornicle secretions using EBF as an alarm pheromone, 2) are less likely to release cornicle secretions when alone than in a small group (~10 individuals), but that the rate of secretion does not increase further with additional conspecific density, and 3) also exhibit alarm reaction behavior in response to cornicle secretions independent of aphid density. We show that soybean aphids can use their cornicle secretions to warn their neighbors of probable attack by natural enemies, but that both secretion and alarm reaction behavior does not change as density of nearby conspecifics rises above a few individuals.

This is the post-print version of the following article: "The Dynamics of Pheromone Gland Synthesis and Release: a Paradigm Shift for Understanding Sex Pheromone Quantity in Female Moths", which has been published in final form at https://link.springer.com/article/10.1007/s10886-018-0963-z; International audience; Moths are exemplars of chemical communication, especially with regard to specificity and the minute amounts they use. Yet, little is known about how females manage synthesis and storage of pheromone to maintain release rates attractive to conspecific males and why such small amounts are used. We developed, for the first time, a quantitative model, based on an extensive empirical data set, describing the dynamical relationship among synthesis, storage (titer) and release of pheromone over time in a moth (Heliothis virescens). The model is compartmental, with one major state variable (titer), one time-varying (synthesis), and two constant (catabolism and release) rates. The model was a good fit, suggesting it accounted for the major processes. Overall, we found the relatively small amounts of pheromone stored and released were largely a function of high catabolism rather than a low rate of synthesis. A paradigm shift may be necessary to understand the low amounts released by female moths, away from the small quantities synthesized to the (relatively) large amounts catabolized. Future research on pheromone quantity should focus on structural and physicochemical processes that limit storage and release rate quantities. To our knowledge, this is the first time that pheromone gland function has been modeled for any animal.

International audience; Most species of moths use a female-produced volatile sex pheromone, typically produced via de novo fatty acid synthesis in a specialized gland, for communication among mates. While de novo biosynthesis of pheromone (DNP) is rapid, suggesting transient precursor acids, substantial amounts of pheromone precursor (and other) acids are stored, predominantly in triacylglycerols in the pheromone gland. Whether these stored acids are converted to pheromone later or not has been the subject of some debate. Using a tracer/tracee approach, in which we fed female Heliothis virescens U-13C-glucose, we were able to distinguish two pools of pheromone, in which precursors were temporally separated (after and before feeding on labeled glucose): DNP synthesized from a mixed tracer/tracee acetyl CoA pool after feeding, and pheromone made from precursor acids primarily synthesized before feeding, which we call recycled precursor fat pheromone (RPP). DNP titer varied from high (during scotophase) to low (photophase) and with presence/absence of pheromone biosynthesis activating neuropeptide (PBAN), in accord with native pheromone titer previously observed. By contrast, RPP was constant throughout the photoperiod and did not change with PBAN presence/absence. The amount of RPP (6.3–10.3 ng/female) was typically much lower than that of DNP, especially during the scotophase (peak DNP, 105 ng/female). We propose an integral role for stored fats in pheromone biosynthesis, in which they are hydrolyzed and re-esterified throughout the photoperiod, with a small proportion of liberated precursor acyl CoAs being converted to pheromone. During the sexually active period, release of PBAN results in increased flux of glucose (from trehalose) and hydrolyzed acids entering the mitochondria, producing acetyl CoA precursor for de novo fat and pheromone biosynthesis.

The peach potato aphid, Myzus persicae is a globally distributed crop pest with a host range of over 400 species including many economically important crop plants. The intensive use of insecticides to control this species over many years has led to populations that are now resistant to several classes of insecticide. Work spanning over 40 years has shown that M. persicae has a remarkable ability to evolve mechanisms that avoid or overcome the toxic effect of insecticides with at least seven independent mechanisms of resistance described in this species to date. The array of novel resistance mechanisms, including several ‘first examples’, that have evolved in this species represents an important case study for the evolution of insecticide resistance and also rapid adaptive change in insects more generally. In this review we summarise the biochemical and molecular mechanisms underlying resistance in M. persicae and the insights study of this topic has provided on how resistance evolves, the selectivity of insecticides, and the link between resistance and host plant adaptation.

BACKGROUND The grain aphid, Sitobion avenae Fabricius (Hemiptera: Aphididae), is an important pest of cereal crops. Pesticides are the main method for control but carry the risk of selecting for resistance. In response to reports of reduced efficacy of pyrethroid sprays applied to S. avenae, field samples were collected and screened for mutations in the voltage-gated sodium channel, the primary target site for pyrethroids. Aphid mobility and mortality to lambda-cyhalothrin were measured in coated glass vial bioassays. RESULTS A single amino acid substitution (L1014F) was identified in the domain IIS6 segment of the sodium channel from the S. avenae samples exhibiting reduced pyrethroid efficacy. Bioassays on aphids heterozygous for the kdr mutation (SR) or homozygous for the wild-type allele (SS) showed that those carrying the mutation had significantly lower susceptibility to lambda-cyhalothrin. CONCLUSION The L1014F (kdr) mutation, known to confer pyrethroid resistance in many insect pests, has been identified for the first time in S. avenae. Clonal lines heterozygous for the mutation showed 35–40-fold resistance to lambda-cyhalothrin in laboratory bioassays, consistent with the reported effect of this mutation on pyrethroid sensitivity in other aphid species. © 2013 Society of Chemical Industry

Most evolutionary research on biological invasions has focused on changes seen between the native and invaded range for a particular species. However, it is likely that species that live in human-modified habitats in their native range might have evolved specific adaptations to those environments, which increase the likelihood of establishment and spread in similar human-altered environments. From a quantitative genetic perspective, this hypothesis suggests that both native and introduced populations should reside at or near the same adaptive peak. Therefore, we should observe no overall changes in the G (genetic variance–covariance) matrices between native and introduced ranges, and stabilizing selection on fitness-related traits in all populations. We tested these predictions comparing three populations of the worldwide pest Myzus persicae from the Middle East (native range) and the UK and Chile (separately introduced ranges). In general, our results provide mixed support for this idea, but further comparisons of other species are needed. In particular, we found that there has been some limited evolution in the studied traits, with the Middle East population differing from the UK and Chilean populations. This was reflected in the structure of the G-matrices, in which Chile differed from both UK and Middle East populations. Furthermore, the amount of genetic variation was massively reduced in Chile in comparison with UK and Middle East populations. Finally, we found no detectable selection on any trait in the three populations, but clones from the introduced ranges started to reproduce later, were smaller, had smaller offspring, and had lower reproductive fitness than clones from the native range.\ud \ud

The aim of this study was to develop a method to cryopreserve the embryos of the pink bollworm moth, Pectinophora gossypiella (Saunders). Previously developed dipteran cryopreservation protocols were not directly adaptable to use with the embryos of this lepidopteran species. Physiochemical and electron microscope observations revealed substantial differences in the structure of the chorion, wax layer, and vitelline membrane complex when comparing the cryopreservable embryonic stages of P. gossypiella and dipteran embryos. Thus, the initial steps dealing with dechorionation and permeabilization were ineffective and had to be altered. Exposure to the sodium hypochlorite-based chorion removal step decreased P. gossypiella embryo viability to a very low level. Survival increased and permeability was evident when an alkane wash was used as the first step in the procedure. After the alkane treatment with a surfactant yielded the maximum exchange of cryoprotectant with water as evidenced by a significant lowering of the supercooling point of the cryoprotectant-loaded embryos. The remainder of the cryopreservation and storage recovery protocol for P. gossypiella was similar to those developed for dipteran embryos. Survival of recovered, hatched embryos to adulthood was approximately 7%.

Over the last 50 years, female-produced sex pheromones of moths have been subjected to intensive study. Most work has focused on their role in mate recognition, and little on any role they may have in mate assessment. This is largely because it has been assumed that female, rather than male, moths are "choosy", and invest larger amounts of carbon in eggs than in pheromone. Recently, we found that pheromone production in the moth Heliothis virescens depended on hemolymph trehalose concentration, and that sugar-stressed females produced less pheromone than unstressed ones. In this paper, we demonstrate, for the first time in moths, that a female-produced pheromone signal can allow H. virescens males to assess sugar resources (quality) of a female. This signal honesty is based on quantitative, rather than qualitative (component ratio), differences in pheromone, produced and released by sugar-stressed and unstressed females. Increasing marginal cost of pheromone production, as sugar resources are depleted, may ensure signal honesty.

Insecticide-resistant clones of the peach-potato aphid, Myzus persicae (Sulzer), have previously been shown to have a reduced response to aphid alarm pheromone compared to susceptible ones. The resulting vulnerability of susceptible and resistant aphids to attack by the primary endoparasitoid, Diaeretiella rapae (McIntosh), was investigated across three spatial scales. These scales ranged from aphids confined on individual leaves exposed to single female parasitoids, to aphids on groups of whole plants exposed to several parasitoids. In all experiments, significantly fewer aphids from insecticide-susceptible clones became parasitised compared to insecticide-resistant aphids. Investigations of aphid movement showed at the largest spatial scale that more susceptible aphids than resistant aphids moved from their inoculation leaves to other leaves on the same plant after exposure to parasitoids. The findings imply that parasitoids, and possibly other natural enemies, can influence the evolution and dynamics of insecticide resistance through pleiotropic effects of resistance genes on important behavioural traits.

Previously, we demonstrated that sex pheromone production in mated female Heliothis virescens moths is dependent upon hemolymph trehalose concentration (HTC), which is influenced by activities such as the feeding of adults on sucrose. In this paper we demonstrate, for the first time, that this effect also occurs in starved (i.e., sugar-stressed) virgin females. Females allowed to feed on sugar for 6 days, following eclosion, had significantly greater titers than females that had fed only on water (i.e., were starved). No differences in pheromone titer were observed between sugar- and water-fed females at shorter (1 or 3 days) periods following eclosion. The relatively short-term effects of HTC on sex pheromone titer of virgins, were demonstrated by feeding experiments, in which starved (for 4 days) virgins fed on 10% sucrose solution had significantly greater HTC and pheromone titers than ones fed only on water; an increase in HTC was apparent within an hour, while the increase in pheromone titer was apparent within 2.5 h, of sugar feeding. Starvation also showed similar effects on titers of pheromone gland fatty acids (pheromone intermediates) and HTC. Over 6 days of starvation, fatty acid titers and HTC declined gradually. After feeding on sucrose, titers of hexadecanoic, (Z)-9-hexadecanoic, (Z)-11-hexadecanoic and (Z)-9-octadecanoic, acids, as well as HTC, increased significantly 24 h later, but titers of octadecanoic and (Z,Z)-9,12-octadecanoic (linoleic) acids did not. Lepidoptera cannot biosynthesize polyunsaturated acids, but the lack of change in octadecanoic acid titer suggests this acid may not participate in pheromone biosynthesis. In addition to these short-term changes in pheromone and fatty acid production, mediated by HTC, a longer-term effect of age, regardless of HTC, on pheromone titer was observed. Overall, these results are consistent with hemolymph trehalose and glandular fatty acids acting as twin metabolite reservoirs for pheromone biosynthesis. Hemolymph trehalose, able to be refilled through feeding on exogenous sugars, has a one-way flow of metabolites for synthesis of glandular free fatty acids (FFAs) and pheromone, while glandular glycerolipids provide a reversible reservoir for metabolites, accepting surplus FFAs when glandular concentrations are high, and providing FFAs for pheromone biosynthesis when concentrations are low.

The preference-performance hypothesis for insect herbivores predicts that adult females should preferentially choose hosts on which their offspring perform better. We tested this hypothesis for the sunflower moth, Homoeosoma electellum (Hulst) (Lepidoptera: Pyralidae), using 16 sunflower (pre-breeding) lines, derived from a number of wild species of Helianthus, including Helianthus annuus L., Helianthus deserticola Heiser, Helianthus paradoxus Heiser, Helianthus praecox Engelm. & Gray ssp. hirtus (Heiser) Heiser, Helianthus praecox Engelm. & Gray ssp. runyonii (Heiser) Heiser, Helianthus petiolaris Nutt., Helianthus resinosus Small, and Helianthus tuberosus L. (Asteraceae), that are suitable for introducing wild sunflower germplasm into commercial cultivars. Female moths showed a range of ovipositional preference measures to the various lines. Combined data for three Helianthus species represented by multiple lines showed significant differences in female preference with respect to the parental species. Larval performance, determined by proportion of infested neonate larvae reaching the pupal stage, or mean pupal weight, varied across the lines and, as for the female preference data, also showed significant differences among the three parental Helianthus species represented by multiple lines. These data suggest that the characteristics in the pre-breeding lines influencing female sunflower moth preference and larval performance likely originate from the parental species and may be consistently transferred to the derived pre-breeding lines. Of particular note with regard to potential plant resistance mechanisms, lines derived from H. tuberosus showed consistent low preference—per— formance measures. Female preference and larval performance (for both measures) were strongly correlated, indicating that females preferred plants and lines on which larvae performed better, in support of the preference-performance hypothesis.

The banded sunflower moth (BSFM), Cochylis hospes Walshingham (Lepidoptera: Cochylidae) is a specialist insect, the larvae of which feed on sunflowers, Helianthus spp., and a few other species of Compositae. It is one of the most important pests of sunflower in the USA. Previous work on H. annuus, the cultivated sunflower, revealed two diterpenoids that function as oviposition stimulants for female BSFM, and that other, more polar compounds also stimulated oviposition. Using a bioassay-guided approach, we isolated three additional diterpenoids, grandifloric acid (1), 15beta-hydroxy-ent-trachyloban-19-oic acid (2), and 17-hydroxy-16alpha-ent-kauran-19-oic acid (3), from polar fractions of pre-bloom sunflower head extracts. In laboratory bioassays, purified natural samples of each of these compounds stimulated oviposition by female BSFM. Structure-activity relationships of the five diterpenoids known to stimulate oviposition by female BSFM are discussed.

BACKGROUND: Although there are still no confirmed reports of strong resistance to neonicotinoid insecticides in aphids, the peach-potato aphid (Myzus persicae Sulzer) shows variation in response, with some clones exhibiting up to tenfold resistance to imidacloprid. Five clones varying in response to imidacloprid were tested with four other neonicotinoid molecules to investigate the extent of cross-resistance. RESULTS: All four compounds - thiamethoxam, thiacloprid, clothianidin and dinotefuran - were cross-resisted, with ED 50 values ranked in the same order as for imidacloprid. Resistance factors ranged up to 11 for imidacloprid, 18 for thiamethoxam, 13 for thiacloprid, 100 for clothianidin and 6 for dinotefuran. CONCLUSION: This variation in response does not appear to be sufficient to compromise the field performance of neonicotinoids aimed at controlling aphids. However, it highlights the need for careful vigilance and stewardship in all M. persicae populations, and a need to consider neonicotinoids as a single cross-resisted group for management purposes.

Asynchronous hatching creates a size hierarchy among siblings and a survival disadvantage for last-hatched nestlings. Female birds can influence this disadvantage by differentially investing maternal resources, such as carotenoids, across the laying sequence. We studied intraclutch variation in carotenoid concentrations in Yellow-headed Blackbirds (Xanthocephalus xanthocephalus) and predicted that yolk concentrations would decrease across the laying sequence, because nestling mortality is inversely related to hatching order in this species. We quantified intraclutch variation in the concentrations of total and individual identifiable carotenoids (β-carotene, β-cryptoxanthin, lutein, and zeaxanthin) in Yellow-headed Blackbird eggs collected from five breeding colonies, and correlated these concentrations with egg mass, yolk mass, and yolk water content. Carotenoid concentrations were not related significantly to any of the egg metrics measured. The concentration of total identifiable carotenoids i...

Recent advances in the characterisation of insect sodium channel gene sequences have identified a small number of point mutations within the channel protein that are implicated in conferring target-site resistance to pyrethroid insecticides (so-called knockdown resistance or kdr). The L1014F (leucine-to-phenylalanine) mutation located in the centre of segment 6 of the domain II region (IIS6) of the sodium channel (the so-called kdr trait) has been detected in the peach-potato aphid, Myzus persicae (Sulzer), and is considered to be the primary cause of pyrethroid resistance in this species. Here we report on the characterisation of a second mutation, M918T (methione-to-threonine), within the nearby IIS4–S5 intracellular linker (the so-called super-kdr trait) in a field clone also possessing L1014F, with both mutations present in heterozygous form. The resistance phenotype of M. persicae clones possessing various combinations of L1014F and M918T to a wide range of pyrethroids (both Type I and II) was assessed in leaf-dip bioassays and to lambda-cyhalothrin applied at up to ten times the recommended field rate as foliar sprays to aphids feeding on whole plants. Bioassay results demonstrated that presence of both mutations was associated with extreme resistance to all the pyrethroids tested relative to aphids lacking the mutations. Furthermore, this resistance well exceeded that shown by aphids that were homozygous for L1014F but lacking M918T. However, pre-treatment with piperonyl butoxide in the leaf-dip bioassays failed to suppress pyrethroid resistance in aphids carrying one or both of the mutations. The relevance of these findings for monitoring and managing pyrethroid resistance in M. persicae populations in the field is discussed.

It has been postulated that sex pheromones, in addition to their role in mate recognition and/or finding, may also serve a role in assessment of mate quality. For this, a sex pheromone must give honest information about a signaler's quality, with honesty ensured by a direct metabolic or indirect fitness cost to the signaler. Using a stable isotope tracer-tracee method, we characterised the nutrient pools that fuel sex pheromone production in females of the moth Heliothis virescens, as well as the relative importance of larval- and adult-acquired nutrients to this process. Females used three pools for de novo biosynthesis of sex pheromone, haemolymph trehalose, glycogen (via trehalose), and fat, and produced ca. 25% of pheromone directly from stored (previously synthesised) precursor fatty acids. Pheromone was produced roughly equally from carbohydrate and fat. Adult feeding was very important for pheromone biosynthesis, with a maximum of 65% of de novo biosynthesised pheromone produced from a single adult feed (carbohydrate). Although these nutrient pools are shared with other reproductive physiologies, notably oocyte production, it is unlikely that pheromone production imposes a significant metabolic cost on females, because (i) the amount of nutrients used for pheromone production is negligible compared to that available, (ii) the haemolymph trehalose pool is readily replaceable throughout the adult life, and (iii) in mated females, carbohydrate shortages result in reduced allocation to pheromone.

Deuterium-labeled hexadecanoic acid (D4-16:COOH), a sex pheromone biosynthetic intermediate, and heptadecanoic acid (D3-17:COOH), an acid that cannot be converted to sex pheromone, were topically applied to the pheromone gland of female Heliothis virescens, and the fate of the label determined. Both acids were incorporated similarly into the glycerolipids, with by far the greatest amount found in the triacylglycerols (TGs), and relatively small amounts found in other neutral and polar classes. For D4-16:COOH, the labeled pheromone precursor, (Z)-11-hexadecenoate, was also found predominantly in the TGs but relatively (compared to labeled hexadecanoate) high amounts were also found in the phospholipids. Within the TGs, both acids, as well as the pheromone precursor, were found almost exclusively on the sn-3 position of the glycerol backbone. This demonstrates that the major fate, in the glycerolipids, of free fatty acids is addition to 1,2-diacylglycerols. A relatively large amount of the applied acid was also found in the gland in the form of the acyl-CoA thioester. In a 24-h time-course study, this form remained at a relatively high level for the duration of the assay, and decreased at a rate comparable to the titer of this acid in the TGs, suggesting that titers of fatty acids in the glycerolipids and acyl-CoA thioesters may be in equilibrium. A time-course assay with D4-16:COOH demonstrated that peak pheromone titer after application was reached before peak titers of both total hexadecanoate and hexadecanoyl-CoA. Combined with a dose-response experiment, which showed that labeled pheromone titer did not increase above an applied concentration of 20 mg/ml, these data suggest that the final step in pheromone biosynthesis, reduction of Z11-16:Acyl-CoA, may be inhibited by increased acyl-CoA titers in the gland. Overall, our data are consistent with the glycerolipids modulating acyl-CoA concentrations in the pheromone gland.

Two diterpenoid alcohols, ent-kauran-16alpha-ol (1) and ent-atisan-16alpha-ol (2), were isolated from pre bloom (R3-R4 stage) sunflower heads as oviposition stimulants for the banded sunflower moth, Cochylis hospes. Fractionation of a sunflower head extract, by normal-phase flash column chromatography, resulted in an early eluting fraction exhibiting significant activity in an egg-laying bioassay. Compounds 1 and 2, along with ent-trachyloban-19-oic acid (3) and ent-kaur-16-en-19-oic acid (4), were isolated as the major components of this fraction and identified by their NMR and mass spectra. The purified compounds were individually tested for ovipositional activity in dose-response bioassays. In these bioassays, compounds 1 and 2 gave linear dose responses, with increasing numbers of eggs laid as the dosage of either increased. Compounds 3 and 4 failed to stimulate significant egglaying at any of the dosages tested. A factorial design bioassay, using compounds 1 and 2, showed that 1 was relatively more stimulatory than 2, and that there was no synergistic effect on oviposition when the two compounds were combined.

A novel beta-lactone, vittatalactone (1), was isolated from collections of airborne volatile compounds from feeding male striped cucumber beetles, Acalymma vittatum. The structure of 1 was determined to be (3R,4R)-3-methyl-4-(1,3,5,7-tetramethyloctyl)oxetan-2-one by microderivatization, GC-MS, and NMR studies. The absolute configurations at C-2 and C-3 on the beta-lactone ring were assigned by use of the modified Mosher method, applied to the beta-hydroxy acid methyl ester resulting from methanolysis of 1. Biological activity of 1, possibly as an aggregation pheromone for A. vittatum, was indicated by electrophysiological studies using beetle antennae and by the production of 1 by feeding male, and not female, beetles.

Binary mixtures of deuterium-labeled palmitic acid and an excess of different fatty acids were applied to the sex pheromone gland of female Heliothis virescens and the effects on the terminal steps of pheromone biosynthesis, including incorporation of fatty acids into the glandular lipids, observed. Relative to labeled palmitic acid applied alone, application of all the binary mixtures resulted in decreased levels of the labeled pheromone component, (Z)-11-hexadecenyl acetate (Z11-16:OAc), but there was generally no decrease in the amounts of labeled pheromone precursor, (Z)-11-hexadecenoate, nor labeled palmitate in the glandular lipids. These data suggest that the excess of fatty acid in the gland inhibits Delta11-desaturation. However, in the case of excess myristoleic acid, the amount of labeled (Z)-11-hexadecenoate increased significantly, suggesting that this acid inhibited fatty acid reduction. Dose-response tests with certain of the fatty acids were consistent with the above interpretations and further indicated that the gland had a high capacity for rapidly activating and incorporating excess fatty acids into the glandular lipids. Finally, application of the various fatty acids resulted in increased levels of these acids in the gland and, in the cases of myristoleic, palmitoleic and myristic acids, it also resulted in increased levels of the corresponding aldehydes, which had previously been detected in the gland of female H. virescens. This suggests that the fatty acid reductase in H. virescens is not highly specific for the major component, and that the final ratio of pheromone components is determined in part by the availability of their corresponding fatty acids in the gland.

The sex pheromone of Cochylis arthuri Dang was identified as a 80:20 mixture of (Z)-11-tetradecenyl acetate (Z11-14:OAc) and (E)-11-tetradecenyl acetate (E11-14:OAc). Cochylis arthuri is a congener of the banded sunflower moth, Cochylis hospes Walsingham, which is a major pest of sunflower, Helianthus spp. (Compositae), in the Great Plains region of North America. Both are found sympatrically on sunflower in this region, although C. arthuri appears to be less common. Field testing of various blends, in sticky traps, showed that a loading of 80 µg Z11-14:OAc and 20 µg E11-14:OAc on a red rubber septum gave the best catches. In field trials in sunflower plots, traps baited with either the C. hospes blend or the best blend tested for C. arthuri only caught significant numbers, relative to blank traps, of males of the respective species, suggesting that the sex pheromones of the two species are specific under those conditions. The identification of an attractive blend of the sex pheromone of C. arthuri will give researchers another tool to investigate the pest status of C. arthuri on sunflowers.

Myzus persicae samples were collected from populations present on a range of field crops between 1997 and 2000. A combination of biochemical, DNA-based diagnostics and bioassays was used to assess the presence of three insecticide resistance mechanisms: elevated carboxylesterase (E4 or FE4), insensitive acetylcholinesterase and insensitive sodium channels (knockdown resistance, kdr). For the carboxylesterases, both the levels of enzyme and the type of gene present (E4 or FE4) were determined. The results showed that during the time period studied there was a dramatic reduction in the proportion of aphids with very high levels of E4 and an increase in those with lower levels of FE4. There was also a slightly different E4 gene present in a limited number of samples. The change in esterase genes was accompanied by a virtual loss of the insensitive AChE variant and a maintenance of aphids with kdr. The selection pressures and other factors leading to these changes in field populations of M persicae are discussed. (C) 2002 Society of Chemical Industry.

Twenty-one clones of the peach-potato aphid, Myzus persicae (Sulzer), carrying various combinations of known mechanisms of insecticide resistance were assessed for their response to the new pyridine azomethine compound, pymetrozine, in leaf-dip bioassays. Pymetrozine was also applied as a foliar spray to populations of four different UK M persicae clones on potato plants in field-simulator chambers. Neither study showed any evidence of cross-resistance to this compound. Pymetrozine, used in conjunction with other effective aphicides, such as pirimicarb and imidacloprid, can therefore play an important role in insecticide resistance-management strategies for M persicae.

Although there has been much investigation of the steps involved in sex pheromone biosynthesis in moths, little is known about the kinetics of biosynthesis in vivo, primarily because there are few techniques suitable for studying the small amounts of pheromone produced without perturbing a female moth's normal physiology. In this paper, female Heliothis virescens moths fed on U-(13)C-glucose were subjected to mass isotopomer distribution analysis, enabling calculation of fractional (FSR) and absolute (ASR) synthetic rates of the main pheromone component, (Z)-11-hexadecenal, at two different photoperiodic times: during the scotophase (when adults are sexually active) and during the photophase (when adults do not engage in mating behavior). FSRs differed substantially at the two times with, as expected, the greater rate occurring during the scotophase. After determining Z11-16:Ald pool sizes, ASR through the scotophase was calculated to be roughly 20 times greater than ASR in the photophase. These differences are consistent with the release/non-release of the pheromone biosynthesis-activating neuropeptide. This approach should facilitate determination of more quantitative measures of semiochemical production in moths and other sugar-feeding insects that synthesize semiochemicals from glycolytic metabolites.

A fully susceptible genotype (4106A) of Myzus persicae survived the longest on an artificial diet and, in several of the eight replicates, monitoring was terminated when the culture was still thriving. A genotype with elevated carboxylesterase FE4 at the R3 level (800F) had a mean survival of only 98.13 days, whereas 794J, which combines R3 E4 carboxylesterase with target-site resistance (knockdown resistance), survived for the even shorter mean time of 84.38 days. The poorer survival of the two genotypes with extremely elevated carboxylesterase-resistance was not the result of a reluctance to transfer to new diet at each diet change. Although available for only two replicates, a revertant clone of 794J (794Jrev), which has the same genotype as 794J but the amplified E4 genes are not expressed leading to a fully susceptible phenotype, did not appear to survive any better than this clone. This suggests that the poor survival on an artificial diet of the extreme-carboxylesterase genotypes is not the result of the cost of over-producing the enzyme. The frequency of insecticide-resistant genotypes is low in the population until insecticide is applied, indicating that they have reduced fitness, although this does not necessarily reflect a direct cost of expressing the resistance mechanism.

Banded sunflower moth, Cochylis hospes Walsingham, is one of the most destructive seed-feeding insect pests of sunflowers, causing significant economic yield losses in the northern Great Plains. In an attempt to understand host-plant resistance mechanisms for this pest, we field-tested, over several years, the effects of seven sunflower accessions, rated as resistant to C. hospes in previous screening trials, and a susceptible control (Par 1673-2), on the ovipositional preference and larval performance of C. hospes and its larval parasitoids. Of the resistant accessions, PI 494859 was the most preferred for oviposition, receiving a significantly greater number of eggs per head than did the susceptible Par 1673-2 in 2 of 3 yr. However, the numbers of larvae, and consequently the rate of seed infestation, found in PI 494859 heads were significantly lower than those in Par 1673-2 heads over all 3 yr. Female moths laid relatively few eggs on accessions PI 170385, 291403, and 251902, compared with on Par 1673-2, resulting in lower numbers of larvae per head and lower percentages of seed damaged. No association was observed between the concentrations of two diterpenoid alcohols or two diterpenoid acids in sunflower bracts and the numbers of eggs laid on the heads of the accessions. The number of banded sunflower moth larvae and the proportion of seeds damaged were positively correlated with kaurenoic acid concentrations and negatively correlated with kauranol concentrations. A positive association between resistance to larval feeding and parasitism was found in years 2006 and 2008, with resistant accessions having significantly greater proportions of parasitized larvae than did the susceptible Par 1673-2.

The peach-potato aphid, Myzus persicae, provides an excellent demonstration of how genetic and ecological factors can interact to determine the dynamics of resistance and influence success of resistance management. The diversity of resistance mechanisms, based on both enhanced detoxification of insecticides and modifications to their target sites, that this species shows is now well understood at the genotypic, biochemical and molecular levels. These developments have yielded rapid and precise methods for detecting individual mechanisms, and for monitoring frequency changes in the presence and absence of insecticide selection. One factor influencing the prediction of these changes in the UK is the occurrence of prolonged periods of parthenogenesis in M. persicae, which results in non-random associations between particular resistance genes through the absence of genetic recombination. This has important implications for the rate at which resistance genes can accumulate in populations under selection by insecticides, and also for the speed at which they will decline when selection is relaxed. Although it is becoming apparent that resistance can be associated with various fitness costs, the relative contribution of individual resistance genes to these effects is still under investigation. However, the overall effect of the `ups’ and `downs’ of resistance in M. persicae, in the UK at least, has been to help maintain resistance phenotypes at manageable levels in most seasons. Unfortunately, the increasing genetic diversity of resistance in this species is progressively eroding the supply of effective insecticides. This in turn highlights the importance of ensuring sufficient chemical diversity to combat existing resistance mechanisms and to restrict the use of novel insecticides in order to sustain their effectiveness.

Bioassay-guided fractionations of a dichloromethane extract of wheat epicuticular wax allowed the identification of 1-octacosanal and 6-methoxy-2-benzoxazolinone (MBOA) as the major components that stimulate oviposition by the Hessian fly, Mayetiola destructor. These compounds were identified by their mass spectral fragmentation patterns and by comparison of their gas chromatographic retention times with synthetic samples. Synthetic samples of 1-octacosanal or MBOA stimulated significant oviposition when compared with solvent controls. In combination, these compounds elicited a synergistic effect on the number of eggs laid by females compared to when they were presented alone. In a choice bioassay, a mixture of synthetic 1-octacosanal and MBOA in the approximate concentrations determined to be present in one plant equivalent of crude extract stimulated the same amount of oviposition as one plant equivalent of extract. This showed that together these two compounds appear to be responsible for the major proportion of the ovipositional stimulatory activity of the wheat epicuticular wax extract. Comparison of the activity of five straight-chain primary aldehydes with chain lengths from C22 to C30 revealed a relationship between chain length and the number of eggs laid by female Hessian flies, with 1-hexacosanal and 1-heptacosanal the most active of the aldehydes tested.

Insecticide sprays were applied to Myzus persicae (Sulzer) populations carrying various combinations of three insecticide resistance mechanisms (esterase-based metabolic resistance and two target site mechanisms, known as MACE and kdr), supported on host plants growing in field simulator cages. The study showed that MACE confers extreme resistance to pirimicarb and triazamate (carbamate insecticides) but not to deltamethrin + heptenophos (16 + 1) (Decisquick) or dimethoate (an organophosphorus insecticide). Resistance to dimethoate depends solely on levels of esterase-based resistance, while resistance to Decisquick depends on kdr and esterase. None of the four insecticides is effective against aphids carrying MACE combined with extreme esterase-based resistance. This knowledge, in association with current monitoring of the mechanisms, will play an important role in making decisions on insecticide use against M persicae in the UK. © 1999 Society of Chemical Industry

When introduced into a wind tunnel with low windspeeds (0.2–0.3 m/sec), neonate E. postvittana larvae were more likely to walk in a downwind rather than upwind direction. This tendency to walk downwind did not change when odors from apple leaves or fruit were introduced into the wind tunnel. In a second assay that measured travel times of larvae as they walked from the center to the edge of filter paper disks, larvae moved more slowly on disks treated with extracts of apple leaves or extracts of apple fruit, but did not slow their movement on disks treated with extracts of a nonhost, Coprosma repens. Analysis of videorecords revealed that larvae on disks treated with a dichloromethane extract of apple leaves took more circuitous routes, walked more slowly, and stopped more frequently than larvae walking on solvent-treated disks. When the dosage of this dichloromethane apple leaf extract was increased or when larvae were held without food prior to testing, differences between travel times on solvent- and extract-treated disks did not increase significantly. The dichloromethane apple leaf extract, when tested in the wind tunnel with low windspeeds, also caused larvae to delay spinning down on a silken thread after reaching the edge of the disk, but had no effect on spin-down times when tested in still-air conditions. Testing of rotary evaporated apple leaf extracts and fractionation of these extracts indicated that a number of both volatile and relatively involatile chemicals contribute to the behavioral responses of E. postvittana larvae.

Sex pheromone-associated behavior of two tortricid moths in New Zealand, Planotortrix notophaea and P. octo , was studied in a laboratory. Most males of both species changed their antennal posture responding to the change from light to dark phase. Three antennal postures in both sexes were designated by dorsal view: antennae in resting position, those extended less than 80° from body axis, and those extended more than 80° from the body axis. In P. notophaea , antennal posture of males appeared as an external indicator representing the physiological readiness for pheromone perception; males with antennae extended more than 80° from the body axis responded better than those in resting position. Bioassays with medicine droppers indicated that threshold concentrations for male response to crude female pheromone extract were 3 × 10 −3 female equivalents (FE) and 3 × 10 −7 FE in P. notophaea and P. octo , respectively. In P. octo , threshold concentrations for male response to known pheromone compounds, (Z)-8-tetradecenyl acetate and tetradecyl acetate, were 10 fg and 100 fg, respectively. Female calling appeared continuous rather than being pulsed. In P. notophaea , stronger male responses were elicited toward females with antennae extended more than 80° from the body axis than those in resting position.

Biosynthesis of the sex pheromone components, (Z)-5-tetradecenyl acetate (Z5-14:OAc) and (Z)-7-tetradecenyl acetate (Z7-14:OAc), was investigated in the New Zealand tortricid moth Planotortrix excessana (Walker) by fatty acid methyl ester (FAME) analysis of base-methanolyzed extracts of lipids in the sex pheromone gland and through application of various labelled fatty acids. Analysis of the base-methanolyzed gland extracts revealed common FAMEs, including methyl oleate and methyl palmitoleate, as well as the FAMEs of the putative precursors, methyl (Z)-5-tetradecenoate and methyl (Z)-7-tetradecenoate. Application of labelled, saturated fatty acids, myristic, palmitic, and stearic did not result in any significant incorporation of label into either of the unsaturated pheromone components, although label was incorporated into tetradecyl acetate (14:OAc). In contrast, application of labelled oleic acid resulted in incorporation of label into Z5-14:OAc but not into Z7-14:OAc or into 14:OAc, whereas application of labelled palmitoleic acid resulted in incorporation of label into Z7-14:OAc but not into Z5-14:OAc or 14:OAc. These data support a route for biosynthesis of Z5-14:OAc and Z7-14:OAc in this species by limited β-oxidation of the common fatty acyl moieties, respectively, oleate (involving two cycles of 2-carbon chain-shortening) and palmitoleate (involving only one cycle of 2-carbon chain-shortening), and apparently involving no desaturase (other than the common Δ9) specific to sex pheromone biosynthesis. Interestingly, P. excessana females biosynthesize the same component (Z5-14:OAc) from an entirely different route from that of the related species Ctenopseustis obliquana (which biosynthesizes Z5-14:OAc by Δ5-desaturation of myristate). Additionally, the pheromone biosynthesis activating neuropeptide (PBAN) stimulates pheromone biosynthesis in this species. Arch. Insect Biochem. Physiol. 37:158–167, 1998. © 1998 Wiley-Liss, Inc.

The peach-potato aphid Myzus persicae (Sulzer) can resist a range of insecticides by over-producing detoxifying esterase and having mutant-insensitive forms of the target proteins, acetylcholinesterase (AChE), and the sodium channel. Using a combination of bioassays, biochemical and DNA diagnostics, it is now possible to diagnose all three mechanisms in individual aphids, and thereby establish their spatial distributions and temporal dynamics. A survey of 58 samples of wide geographic origin showed that all 46 resistant clones had amplified esterase genes (E4 or FE4) conferring broad-spectrum resistance to pyrethroids, organophosphates and carbamates. These occurred in combination with insensitive AChE (11 clones), conferring resistance to pirimicarb and triazamate, and/or mutant sodium channel genes (25 clones), conferring knockdown (kdr) resistance to pyrethroids and DDT. Amplified esterase genes were in linkage disequilibrium with both insensitive AChE and the kdr mutation, reflecting tight physical linkage, heavy selection favouring aphids with multiple mechanisms, and/or the prominence of parthenogenesis in many M. persicae populations. An ability to monitor individual mechanisms with contrasting cross-resistance profiles has important implications for the development of resistance management recommendations.

Sex pheromone titre in the tortricid moth Epiphyas postvittana follows a pattern commonly observed in other species of moths: an increase to a peak some time after eclosion (2–3 days), and then a slow decline as the female ages. Previous work has shown that this decline is not regulated by the pheromone biosynthesis activating neuropeptide PBAN. Using in vivo and in vitro enzyme assays, and fatty acid methyl ester (FAME) analyses of pheromone precursors in the gland, we have investigated this senescent decline in pheromone titre. The enzyme assays have shown that in older females the fatty acid reductase and fatty acid synthesis enzyme systems decrease in activity (relative to younger females), whereas other enzyme systems involved in pheromone biosynthesis, including limited β -oxidation (2-carbon chain-shortening), ( E )-11-desaturation, and acetylation (by an acetyl transferase) remain unchanged in their activity. Of the two enzymatic processes involved, the more important one contributing to the decline appears to be the fatty acid reductase. This is consistent with FAME analyses of pheromone glands in old and young females, which show little difference in levels of saturated FAME, but a significant increase in the level of the putative precursor, ( E )-11-tetradecenoate, of the sex pheromone component ( E )-11-tetradecenyl acetate. Thus, this decline in fatty acid reductase activity results in a buildup of the precursor as the female ages. The near ubiquity of fatty acid reductases in moth sex pheromone systems suggests that this may be a common mechanism for the senescent decline of sex pheromone titre in moths.