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The western spotted cucumber beetle, Diabrotica undecimpunctata undecimpunctata Mannerheim, is an important pest of melons (Cucurmis melo L.) in northern California. Recent observations indicate that adults are using alfalfa (Medicago sativa L.) as a feeding host and larvae may be developing on the roots. Greenhouse studies were conducted during the winters of 2009 and 2010 in which larval development was compared on the roots of six field and vegetable crops commonly grown in the southern Sacramento Valley. The growth parameters used to evaluate the hosts were larval and pupal head capsule width, body width, and body length as well as total survival percentage and survival percentage to the third instar. According to larval growth and survivorship in 2009, maize (Zea mays L.) was the best host, followed by alfalfa and tomato (Solanum lycopersicum L.) that were roughly equivalent to one another. Melon was a slightly weaker host than alfalfa and tomato; sunflower (Helianthus annuus L.) was a completely incompatible host and thus dropped from the 2010 study. In 2010, melon was the weakest host for larval development. Maize was the superior host again followed closely by alfalfa that performed slightly better than tomato and lima bean (Phaseolus lunatus L.). Data suggest that larval western spotted cucumber beetles may primarily develop outside of melon fields and the adults emigrate to melons.

Aggregation behavior of adult western spotted cucumber beetles (Diabrotica undecimpunctata undecimpunctata Mannerheim) (Coleoptera: Chrysomelidae) was examined in six snap bean (Phaseolus vulgaris) fields adjacent to corn fields in western Oregon in 2004-2006. In the 2004 and 2005 studies, sweep net sampling was used to estimate beetle numbers along transect lines running perpendicular to the edges of the bean fields next to sweet corn fields. Beetles were collected from the fields and dissected to determine sex and egg development. Beetles were highly aggregated along the edge of the snap bean field next to the sweet corn, with the highest number of beetles occurring within the first meter next to the edge. Beetles in the aggregation areas were mostly females (average female to male ratio of 8.4 to 1), whereas beetles in the field section away from the edges were mostly male (female to male ratio of 0.6 to 1). Of the females collected in the aggregation areas, an average of 53% contained developing or fully developed eggs. In the 2006 study, beetle densities in the field edges were compared with densities within the fields in 40 bean fields with adjacent corn fields. Linear regression analysis showed that, across fields, nearly two times as many beetles were found in the field borders as in the rest of the field. These data suggest modifying traditional field scouting protocol to include field margins when a bean field is adjacent to or near a sweet corn field. A pest management strategy of only spraying the edges of bean fields containing beetle aggregations shows potential for significant pesticide reduction, as well as reducing risk of economic loss from crops harvested from the highly aggregated areas.

Adult females of many arthropods require high food intake for producing eggs, whereas males feed less and spend more time searching for mates. If males and females differentially prioritize activities, they may experience a different ratio of costs to benefits of antipredator behaviors. We investigated sexual differences in the behavioral responses of spotted cucumber beetles, Diabrotica undecimpunctata howardi Barber, to the spider Rabidosa rabida Walckenaer in laboratory arenas in which the beetle could detect the spider, but the spider was prevented from preying upon the beetle. In structurally simple arenas with a single plant, the presence of a spider caused female beetles to spend less time on the plant, and to feed less when on the plant. In contrast, male beetles did not alter their behavior in response to the spider. A second experiment used larger arenas, in which the beetle could choose between a side containing a plant with a spider at its base, and the other side with no spider. Female cucumber beetles spent less time on the side with the spider, whereas males did not consistently change their behavior in response to the spider. The weaker antipredator response of males leads to a greater predation risk, as revealed by a third experiment in which predation was allowed. In this experiment males were 16 times more likely than females to be killed by R. rabida, demonstrating that the lower responsiveness of male beetles to predators increases the risk of being preyed upon.

Larval host associations in luperine rootworm beetles (Chrysomelidae), including the many pest species in the subtribes Diabroticina and Aulacophorina, remain largely unknown because adults often feed on plant species and families other than those favored for larval development. Because important questions concerning the evolutionary origins, systematic relationships, and pest management of luperine rootworms require knowledge of their larval host associations, techniques that enable inference of larval host use from adult structures are needed. Using spotted cucumber beetle, Diabrotica undecimpunctata howardi Barber, and striped cucumber beetle, Acalymma vittatum (F.), as model species, this study confirms that the stable carbon isotopic signature of adult elytra (the ratio between 13 C and 12 C isotopes, expressed as δ 13 C) accurately reflects whether an individual consumed C 3 plants throughout its life, C3 plants as a larva and C 4 plants as an adult, or C 4 plants exclusively. The study also demonstrates that, because the δ 13 C of elytra is unaffected by time, easily accessible museum specimens can be used for δ 13 C assays.

The influence of kairomonal baits, containing cucurbitacins, blossom volatiles, and carbaryl, on Diabroticite adult survivorship and trophic interactions with cucurbits was examined. Enrichment of cantaloupes using rubidium (Rb) was developed for monitoring trophic interactions. A soil-soak method was developed to enrich plant Rb concentrations. Beetle uptake of Rb followed a rectangular hyperbola and elimination after transfer to clean plants followed an exponential decay. Models showed beetle uptake occurred within 1 h and the mark is retained up to 2 wk. Naturally occurring endogenous Rb concentrations in beetles varied with species and sex. Baselines were established to allow determination of the incidence and intensity of beetle feeding on Rb-enriched plants. In field cages, kairomonal baits reduced the probability and intensity of feeding on cucurbits by Diabrotica undecimpunctata howardii (Barber) and Acalymma vittata (F.). In one trial, kairomonal baits totally blocked feeding interactions. In field plots, baits also significantly reduced feeding incidence and intensity in D. u. howardii and D. virgifera virgifera (LeConte), but not in A. vittata. Where the bait reduced feeding, males showed less reduction than females. In D. v. virgifera , there was a higher probability of capturing live males than females regardless of kairomonal treatment. Adult survivorship was reduced by the kairomonal bait in both field and cage experiments. These novel methods allow the monitoring of trophic interactions under field conditions in the presence of behavior-modifying semiochemicals. Hypotheses to explain variation among species and sex and implications of using kairomonal baits to manage vectoring of a pathogen are discussed.

Laboratory assays were conducted to determine effect of host plant on mortality of the southern corn rootworm, Diabrotica undecimpunctata howardi Barber, from the entomopathogenic nematodes Steinemema carpocapsae Weiser and Heterorhabditis bacteriophora Poinar and on nematode progeny production. Mortality of D. u. howardi , as well as nematode progeny production, varied according to the host plant on which the rootworms had fed. Mortality from S. carpocapsae was lower for rootworms that had fed on peanut roots than for rootworms that had fed on squash or com roots. Mortality from H. bacteriophora was lower for rootworms that had been reared on corn roots than for rootworms that had fed on peanut or squash roots. For both nematodes, progeny production from larvae that had fed on squash roots was significantly lower than progeny production from rootworms that had fed on com or peanut roots. Host plant effects involving entomopathogenic nematodes and a soil-inhabiting stage of an insect pest have not been previously demonstrated.

Cucurbitacins, toxic to most organisms, are arrestants and phagostimulants for diabroticite chrysomelid beetles. Little is known about variation in the response of diabroticites to cucurbitacins. To quantify the effects of age, sex, reproductive status, and prior exposure to cucurbitacins on the sensitivity to cucurbitacin B of the southern corn rootworm, Diabrotica undecimpunctata howardi Barber, beetles were separated by sex and grouped for treatment with diets including or excluding cucurbitacins. Sensitivity to cucurbitacins was assayed over the first 43 d of adulthood by exposing beetles in groups of five for 24 h to filter paper strips spotted with serial methanol dilutions of cucurbitacin B ranging from 800 to 0.1 ng/ml. The areas consumed by the beetles at each dilution were then measured, and dose-response curves for each treatment were drawn. Treatments were compared in terms of the area under the mean dose response curve (AUC). Sex, age, reproductive activity, and prior exposure to cucurbitacins all significantly affected beetle sensitivity, though prior exposure was the most consistent in its effect. Exposure to cucurbitacins for as little as 6 d permanently reduced sensitivity, whereas beetles without prior exposure remained sensitive to our assay throughout the study. Reproductive activity depressed sensitivity in males but increased sensitivity in females. These results are discussed in terms of their relevance to semiochemical diabroticite baits and also to the proposed role of cucurbitacins in protecting these beetles from predators, parasites, or pathogens.

Laboratory, greenhouse, and field studies were conducted to determine whether the eggs of southern corn rootworm, Diabrotica undecimpunctata howardi Barber, from adults that had fed on a bitter (cucurbitacin C-containing) cucumber variety experience less predation than eggs from beetles that had fed on a nonbitter (noncucurbitacin C-containing) cucumber variety. Human taste tests and insect bioassays indicated the presence of cucurbitacin in the “bitter” eggs. Eggs from adults that had fed upon bitter and nonbitter cucumber cotyledons and early foliage were placed into soil at three different distances from one another and at four different density combinations of bitter:nonbitter eggs. There were no significant differences in predation of eggs by any of the four arthropod predators tested caused by cucumber variety or by egg distance and density. In a laboratory experiment, eggs from adults feeding on bitter and nonbitter cucumber varieties were compared for percentage egg hatch without moisture stress (held at 100% RH) or stressed for 6, 12, or 18 h at 94% RH before being held at 100% RH. Bitter eggs in both unstressed and stressed for 6 h treatments hatched significantly earlier than nonbitter eggs. There was no significant difference in hatched rate between bitter and nonbitter eggs stressed for 12 or 18 h. The presence of cucurbitacin C does not appear to protect southern com rootworm eggs from predation by the arthropod predators tested compared with nonbitter eggs. However, more rapid development and earlier eclosion of bitter eggs relative to nonbitter eggs may help bitter eggs survive in soils that fluctuate between dry and moist conditions.

The below-ground effects of weeds ( Amaranthus retroflexus L., Chenopodium album L., Ambrosia artemisiifolia L., Digitaria sanguinalis L., Setaria viridis L., Panicum dichotomiflorum Michx.) and increased soil moisture on damage to peanut pods by southern corn rootworm, Diabrotica undecimpunctata howardi Barber, was investigated in a 2-yr field and greenhouse study. Field experiments demonstrated that weedy areas had less pod damage overall and higher predator numbers than nonweedy areas. However, increased soil moisture, which increased southern corn rootworm oviposition and egg and larval survival, confounded the results. Greenhouse studies showed that three broadleaf species and three grass species were not as good food sources as peanuts for southern corn rootworm larvae. Although the presence of weeds growing with peanuts did not lower larval survival, weeds did significantly ( P ≤ 0.05) slow larval developmental rate. In greenhouse studies, damage to peanut pods was approximately 66% in peanut-only (control) treatments, 55% in peanut + weed treatments, 32%in peanut predator treatments, and 9%in peanut + weed + predator treatments. The interaction of predators and weeds in lowering the amount of damage caused by southern corn rootworm was significant ( P ≤ 0.05). Field and greenhouse experiments demonstrated that at least two factors were operating to reduce pest damage in this belowground, multispecies plant association. Predators and the structural complexity of the weed-crop root association may be working synergistically to reduce southern corn rootworm damage to peanuts.

Laboratory studies showed that the soybean phytoalexin glyceollin, an isoflavonoid previously investigated as an inhibitor of fungal pathogens, is an effective antifeedant for some insect species. Glyceollins extracted from soybean, Glycine max Merrill, cotyledons were applied to the surface of common bean leaves, Phaseolus vulgaris L., in five concentrations, including physiological concentration, for feeding preference tests. Leaves treated with glyceollin at concentrations below physiological levels were less acceptable to the southern corn root worm, Diabrotica undecimpunctata howardi Barber, and the Mexican bean beetle, Epilachna varivestis Mulsant, than untreated leaves. Feeding deterrence was positively correlated with increasing concentrations. The bean leaf beetle, Cerotoma trifurcata Forster, was not affected even by very high doses. An ethological concentration (EC 50) was computed based on the log dose–reduction of acceptance of treated disks. The EC 50 for the Mexican bean beetle was 6.1 μg/mg leaf dry weight and 3.5 μg/mg for the southern corn rootworm. Results indicate that soybean phytoalexins may represent a common defense against microorganisms and insect herbivores.

Oviposition preferences of the southern corn rootworm, Diabrotica undecimpunctata howardi Barber, were investigated in greenhouse experiments where abiotic and biotic parameters were manipulated. Southern corn rootworm oviposition distance from corn seedlings was quantified. Four soil moistures, four soil textures, and the presence of weeds were examined in caged greenhouse experiments for their effect on southern corn rootworm oviposition preference. Additional experiments were conducted to elucidate southern corn rootworm oviposition preference for corn seedlings in the presence of broadleaf weeds, grass weeds, a wheat straw cover, or bare soil in large-cage experiments in the greenhouse. Southern corn rootworm adults oviposited >90% of their eggs within 3 cm of a corn stem with

Greenhouse studies were conducted to determine the effects of four soil textures and four soil drying periods on southern corn rootworm, Diabrotica undecimpunctata howardi Barber, egg and larval survival and maturation. Soil drying intervals had the most detrimental effect on survival. After 4 d of soil drying (no water added to pots), only 20% of larvae survived to pupation. Low clay or organic matter and low levels of soil moisture were not conducive to survival of southern corn rootworm. The interaction of soil texture and soil drying indicates that at 4 d of soil drying, larval survival decreased (70%) in all soils, except dark-textured soils (35% decrease) compared with 2 d of soil drying. Low levels of soil moisture slowed developmental time of larvae. Eggs and first instars were the stages most negatively affected by moisture stress and different soil textures. However, in quartz-sand, the more mobile stages had low survival, probably because of cuticle abrasion from soil particles. The results of these experiments demonstrate the importance of considering the effects of rapidly drying soil on survival of southern corn rootworm and not simply the percentage of soil moisture at any one time.

Rate of development and the survival of pupae of Diabrotica virgifera virgifera LeConte and D. undecimpunctata howardi Barber were studied under numerous constant temperature and humidity regimes. Temperature range for maximum survival, as measured by eclosion, was 18–30°C for D. v. virgifera and 15–30°C for D. v. howardi. Time of development within these temperature ranges was similar for both species (5–10 days). At all temperatures studied, a saturated atmosphere (100% RH) was optimal for pupal survival and development.

Spotted and banded cucumber beetles, Diabrotica undecimpunctata howardi Barber and D. balteata LeConte, cold-acclimated and nonacclimated, shared a common range of supercooling points (−12 to −14°C); however, LD50 values showed that cold-temperature survival of the spotted cucumber beetle was higher relative to the banded cucumber beetle as the exposure temperature approached O°C. A considerable portion (41.5%) of spotted cucumber beetle adults survived ambient conditions during the winter of 1988 at Charleston, S. C, whereas all adults of the banded cucumber beetle died. Reproductive diapause did not contribute to cold hardiness in the spotted cucumber beetle, but cold acclimation increased survival to exposures of −10°C in both species.

Eighteen species of Cucurbita were examined qualitatively for spectrum of cucurbitacins present and quantitatively for the amounts in leaves, fruits, and roots by means of thin-layer chromatography, mass spectrometry, and ultraviolet absorption spectrometry. Crumpled leaves and sliced fruits of the various species were exposed to large populations of the southern cornrootworm (SCR), Diabrotica undecimpunctata howardi Barber, and the western cornrootworm (WCR), D. virgifera LeConte. There was a strong correlation between the total cucurbitacin content and the extent of aggregation and feeding by both SCR and WCR.

Phytophagous insect associations with 5 cultivated and 14 mesophytic and xerophytic wild Cucurbita spp. were recorded for 4 consecutive years. Overwintering striped cucumber beetles, Acalymma vittata (Fab.) were most attracted to the young growth of the Maxima and Ficifolia groups and the wild xerophytic Digitata group. Foliage feeding responses were strongest on the latter group. The spotted cucumber beetle, Diabrotica undecimpunctata howardi Barber, exhibited a high affinity for the Maxima, the wild Lundelliana and Digitata groups. The squash vine borer severly injured the Maxima and Pepo groups. The squash bug, Anasa tristis (DeGeer), showed a high ovipositional preference for the Maxima and Mixta groups and a low preference for all other groups. All Cucurbita spp. were poor hosts for the melon aphid, Aphis gossypii (Glover), with the wild Sororia and Ficifolia groups most suitable for reproduction. The potato leafhopper, Empoasca fabae (Harris), preferred cultivated species but oviposited on all wild species except C. foetidissima (HBK). The potato aphid, Macrosiphum euphorbiae (Thomas), preferred the Sororia and Pepo groups. Principle component analysis revealed that the striped cucumber beetle, squash vine borer and the squash bug showed similar host preference patterns with the Maxima group being the most favored.

Intra- and interplant distribution of five pest species of insects were evaluated in research plots planted to cantaloupe, Cucumis melo L., over three growing seasons, fall 1983 and spring 1984 and 1985. Two species, Diabrotica undecimpunctata howardi Barber, spotted cucumber beetle; and Empoasca abrupta DeLong, western potato leafhopper, were found to be randomly dispersed. One species, Aphis gossypii Glover, melon aphid, was found to be overdispersed, and two species, D. balteata LeConte and Acalymma vittatum (F.), banded and striped cucumber beetles, respectively, varied between random and overdispersed. One species, melon aphid, was found to be most abundant on the basal portion of vines. Precision of sampling techniques for each species was evaluated using relative variation and it was determined that sampling precision could be increased by reducing area sampled and increasing the number of samples.

Winter legume and grain cover crops preceding corn, Zea mays L., grown using conventional and no-tillage methods were investigated for their effect on population dynamics and community structure of soil arthropods. Hairy vetch, Vicia villosa Roth, supported higher below-ground arthropod population densities and a more taxonomically diverse fauna than crimson clover, Trifolium incarnatum L., or wheat, Triticum aestivum L. Pest and beneficial soil arthropods were most abundant in no-tillage corn preceded by hairy vetch. Diversity of soilarthropod species was higher under no-tillage than conventional tillage. Divergences in community structure of soil arthropods among cover crop species, evident early in the season, dissipated by midseason. Arthropod predators were more numerous in no-tillage than conventional tillage systems regardless of previous cover crops. Although no-tillage practices promoted a more trophically balanced soil arthropod community than conventional tillage during early and mid season, in 1987 seedling corn plants in no-tillage vetch treatments sustained significantly higher (P < 0.05) damage from the southern corn rootworm, Diabrotica undecimpunctata howardi Barber, than in other treatments. Tillage system preference was shown by herbivores: Seedcorn maggot, Delia platura (Meigen), occurred in large numbers in conventional tillage, and southern corn rootworm populations were high in no-tillage, especially following legume cover crops.

Bacteria in the guts of southern corn rootworms, Diabrotica undecimpunctata howardi Barber, feeding on artificial diet (AD larvae) and on corn roots (CR larvae) were studied. Species composition and abundance of gut-inhabiting bacteria differed between AD larvae and CR larvae. The total bacterial population in AD larvae was about 100 times less than those in CR larvae. The majority of bacterial species found in the gut of CR larvae were glucose fermenters, whereas the major bacteria found in AD larvae were fluorescent pseudomonads. Enterobacter cloacae was predominant among glucose-fermenting bacteria in CR larvae. Pseudomonas putida, P. fluorescens , and Agrobacterium sp. were major bacteria in the glucose nonfermenting bacteria group in CR larvae and AD larvae. The numbers of fluorescent Pseudomonas spp. and Agrobacterium sp. found in CR larvae were positively correlated with their population on corn roots.

Southern corn rootworm larvae and pupae survived best in a controlled soil environment with plant-available water (PAW) ranging from 70 to 100%. Survivability was significantly inferior at the 45 to 55% or 20 to 30% PAW range. Percent clay in southeastern Virginia soils had a less dramatic but significant effect on survivability with the highest clay content soils allowing the best survival. Abrasiveness of soils for peanut production in southeastern Virginia was not believed to be important in immature rootworm survival, but particle size as related to its water holding capacity was important.

Crude extracts of five plant species which in previous experiments significantly limited corn wireworm, Melanotus communis Gyllenhal, feeding damage were tested for deterrence of the southern corn rootworm, Diabrotica undecimpunctata howardi Barber. When offered extract-treated and untreated corn seeds, rootworms damaged significantly fewer treated seeds than untreated seeds with four of the extracts. In a “no-choice” test design, with the three most effective extracts, there was a significantly lower frequency of damage to treated baits compared to control baits.

In a 2-year study, fruits from 21 plant types of 15 species from 6 genera ( Citrullus, Cucumis, Cucurbita, Lagenaria, Luffa , and Momordica ) of Cucurbitaceae were exposed to a natural population of Diabrotica undecimpunctata howardi Barber to determine relative attractance of thc fruits to that insect. Analysis of cucurbitacins and their glycosides in the fruits revealed a positive correlation between their concentration and the number of spotted cucumber beetles attracted by the various plant species. This correlation dcmonstrated the attraction properties of low concentration (0.0–0.56 mg/g) of curcurbitacins and their glycosides. Cucurbita foetidissima H. B. K. and Cucumis dipsaceus Ehrenb., the 2 most attractive species, were high in cucurbitacin concentration. The technique of exposing fruits to D. undecimpunctata howardi has potential as a bioassay to screen cucurbitacins in the fruits of other species. Attractant cucurbitacins can be useful in population assessment and in luring the beetle to an insecticide or to an adhesive.