Effect of dietary selenium supplementation on resistance to baculovirus infection

We have examined the effects of dietary selenium (Se) supplementation on larval growth and immunocompetence of the lepidopteran pest, the cabbage looper, Trichoplusia ni. Supplementation of the diet of T. ni larvae with 10–20 ppm Se resulted in a 1 day delay in pupation. The effects of the addition and/or removal of dietary Se on total Se bioaccumulation and sequestration were determined by neutron activation analysis of pupae. Early penultimate instar larvae moved from selenium containing diet to basal diet lost total pupal Se content down to the level of those fed basal diet. Conversely, larvae moved from basal diet to diet containing additional Se rapidly attained pupal Se levels comparable to larvae fed Se throughout larval development. Therefore, dietary Se is rapidly accumulated or lost during larval development, but significant amounts are sequestered from diet into pupae. Larvae were reared on diet supplemented with 5 or 10 ppm Se until the onset of the penultimate instar then infected per os with increasing concentrations of the fatal baculovirus Autographa californica multiple nucleopolyhedrovirus (AcMNPV). Larvae fed Se in the penultimate and ultimate instars were more resistant to viral infection than larvae not fed Se in the final instars. This study indicates that dietary Se levels rapidly impact Se assimilation and sequestration and that tissue Se levels are an important factor in resistance to AcMNPV infection in larval T. ni.     

Antibiosis in Soybean Genotypes and the Resistance Levels to Spodoptera eridania (Cramer) (Lepidoptera: Noctuidae)

The southern armyworm (SAW) Spodoptera eridania (Cramer) is one of the most common armyworm species defoliating soybeans. Preliminary screening trials have indicated that some soybean genotypes exhibit resistance to SAW. Therefore, in this study, we evaluated the development of SAW larvae fed on ten soybean genotypes in order to identify genotypes with antibiosis-type resistance. Neonate SAW larvae were daily fed with young leaves collected from plants at the vegetative growth stages V4–V5. Larval development and survival were recorded. Genotypes PI 227687 and PI 227682 delayed larval, pupal, and larva-adult development and yielded larvae with the lowest weight and survival and pupae with the lowest weight. Genotypes IAC 100 and DM 339 also negatively affected larval and pupal development and larval survival but at a lower level. Based on our results, the soybean lines PI 227687 and PI 227682 could be used as sources of genes for soybean breeding programs aiming to develop high yield, SAW-resistant cultivars. Moreover, further trials must be carried out under field conditions to validate if the commercial cultivars IAC 100 and DM 339, which expressed moderate levels of antibiosis-type resistance in the laboratory, are effective in suppressing SAW larvae populations.     

Role of trichomes in soybean resistance to cabbage looper, Trichoplusia ni

Role of leaf trichome density and length in Glycine max (L.) Merr. resistance to Trichoplusia ni (Hübner) was evaluated at different leaf positions on a relatively resistant soybean, plant introduction (PI) 227687, and a relatively susceptible cultivar, Davis. The uppermost (juvenile) leaf within both PI 227687 and Davis plants, which is densely covered with trichomes, was most resistant to T. ni larval feeding and survival. When these trichomes were shaven off, such leaves became as susceptible to T. ni larval feeding as unshaven TL3 and TL5 leaves (PI 227687) or all other unshaven leaves (Davis). Bioassays for antifeedants in ethyl acetate and hexane extractables from leaves at the different positions on PI 227687 and Davis plants showed that the resistance observed in the uppermost Davis leaf is attributable to trichomes (i.e., a morphological factor); whereas, in the uppermost PI 227687 leaf it involves both morphological (trichomes) and chemical factors, but the trichome parameter is dominant.

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Résumé L'influence de la densité et de la longueur des trichomes de Glycine max sur la résistance à Trichoplusia ni a été évaluée suivant la position des feuilles sur une lignée résistante (PI 227687) et sur un cultivar sensible (Davis).Les feuilles apicales (juvéniles) tant de PI 227687 que de Davis, recouvertes de trichomes denses, résistèrent mieux à l'alimentation larvaire et à la survie de T. ni.Quand ces trichomes étaient éliminés, ces feuilles ne résistaient pas plus à l'alimentation des larves de T. ni que les feuilles non rasées TL3 et TL5 de PI 227687 ou toutes les autres feuilles de Davis.Les tests avec des extraits dans l'acétate d'éthyle et l'hexane de feuilles provenant de différentes positions de PI 227687 et Davis, destinés à mettre en évidence des phagodissuadants, ont montré que la résistance observée chez les feuilles apicales de Davis était attribuable aux trichomes (c'est-à-dire à un caractère morphologique), tandis que chez les mêmes feuilles de PI 227687 elle impliquait à la fois des trichomes (morphologie) et des substances chimiques, mais avec une prédominance de l'influence des trichomes.

     

Baculovirus-resistant Anticarsia gemmatalis responds differently to dietary rutin

The velvetbean caterpillar, Anticarsia gemmatalis (Hübner) (Lepidoptera: Noctuidae), the major soybean [Glycine max (L.) Merrill (Fabaceae)] defoliator pest in Brazil can be controlled by a specific and virulent nuclear polyhedrosis virus (AgMNPV). Flavonoids such as rutin (quercetin 3‐O‐rhamnosylglucoside) were identified in soybean; it is known that this compound plays an important role in plant defense against lepidopteran pests. Studies were carried out to evaluate the biological and physiological activity of rutin (0.65 and 1.30%) on populations of A. gemmatalis resistant and susceptible to AgMNPV. Larvae from the resistant population were more negatively influenced by rutin, in comparison to larvae of the susceptible population, even with the addition of the lowest level of the flavonoid (0.65%) to the insect diet. The highest mortality (98%) was observed in the resistant population, when larvae fed on the diet containing 1.30% of rutin. Elongation of the feeding time, smaller initial larval weight, and pupal weight was observed on the virus‐resistant and ‐susceptible populations after adding 0.65 and 1.30% rutin to the diet. Larvae of the resistant population to AgMNPV fed on diet plus rutin 0.65% were also less efficient in the conversion of ingested and digested food into biomass.     

Spruce budworm growth,development and food utilization on young and old balsam fir trees

Laboratory rearing of spruce budworm, Choristoneura fumiferana, in conjunction with field rearing, gravimetric analyses, a transfer experiment, and foliage chemical analyses at six dates during the period of budworm feeding activity indicated that the age of balsam fir, Abies balsamea, trees (70-year-old mature trees or 30-year-old juvenile trees) affected tree suitability for the spruce budworm via the chemical profile of the foliage. Insects reared on old trees had greater survival and pupal weight, shorter development times, and caused more defoliation than those reared on young trees. Young trees were more suitable for the development of young larvae (instars 2–5), while old trees were more suitable for the development of older, sixth-instar larvae. These results were confirmed by the laboratory transfer experiment. Young larvae fed foliage from young trees had higher relative growth rates (RGR), digestibility (AD), and efficiency of conversion of ingested foliage (ECI) than those fed foliage from old trees. These differences appeared to be related to the high N:tannins ratio, and the high contents of P present in young trees during the development of the young larvae. Old larvae fed foliage from old trees had higher relative growth rates, relative consumption rates (RCR), and digestibility of the foliage than those fed foliage from young trees. The high digestibility of the foliage of old trees was compensated for by a lower efficiency of conversion of digested food (ECD), which in turn resulted in no significant effect of tree age on the efficiency of conversion of ingested foliage by old larvae. The low relative consumption rate of old larvae fed foliage from young trees appeared to be related to the low N:tannins ratio, and the high contents of bornyl acetate, terpinolene, and °-3-carene present in young trees during the budworm sixth instar. Variations in these compounds in relation to tree age may serve as mechanisms of balsam fir resistance to spruce budworm by reducing the feeding rate of sixth instar larvae.     

Generalized plant defense: effects on multiple species

Summary Two species of lepidopteran herbivores, Manduca sexta (Sphingidae) and Trichoplusia ni (Noctuidae), were reared on synthetic diet containing either the alkaloid nicotine or the flavonoid rutin. Survival and pupal weight of the specialist M. sexta did not differ when larvae were reared on diet containing nicotine or rutin. In contrast, the generalist T. ni did not survive on diet containing 0.125% nicotine or greater, whereas larvae survived on all concentrations of rutin. These data demonstrate that the alkaloid nicotine is inhibitory toward generalist, but not specialist herbivores, whereas the flavonoid rutin has no effect on specialist herbivores and limited effects on generalist herbivores. Five species of Pseudomonas bacterial pathogens: P. syringae, P. syringae pv. angulata, P. syringae pv. tabaci, P. fluorescens, and P. solanacearum were grown on nutrient agar containing nicotine or rutin at concentrations ranging from 0.0 to 1.0% wet weight in 0.1% intervals. No species of Pseudomonas grew at concentrations greater than 0.5% nicotine when 10⁶ colony forming units (cfu) were used, but growth occurred at all concentrations of rutin when 10² cfu were used. These data indicate that nicotine was inhibitory to growth of both herbivores and pathogens, suggesting that certain plant secondary chemicals with high toxicity are of a generalized nature and affect multiple species. Differences in the sensitivity of organisms to allelochemicals such as generalist or specialist can make it appear that specific allelochemicals affect specific organisms, when in fact it is the tolerance of the organism to the plant chemical that is responsible. In four separate studies, the growth of M. sexta, T. ni and Helicoverpa zea was significantly lower on plants inoculated with P. solanacearum. Alteration in leaf quality by P. solanacearum was due to either reductions in leaf nutrients or increases in allelochemicals. We speculate that localized or systemic induction by both herbivores and pathogens can cause changes in leaf quality, effecting each other's subsequent colonization. The generalized nature of plant secondary compounds and potential reciprocal effects on induction by both species suggests that herbivores and pathogens may affect plant quality through induction and diffuse interactions of disparate species can alter the community of organisms colonizing a plant.     

Effects of two artificial diets on the development and reproduction of Tirathaba rufivena (Walker) (Lepidoptera: Pyralidae)

Growth, survival, fecundity, and nutrition of Tirathaba rufivena (Walker) fed on two artificial and one natural diet were studied at 29±1°C and 75±5% relative humidity. Larvae reared on the two artificial diets showed faster growth and development, higher pupal survival and weight, and higher adult fecundity than those reared on a natural diet of young coconuts, Cocos nucifera L. The relative growth rate, efficiency of ingested food conversion, and efficiency of digested food conversion in larvae fed on artificial diets were significantly higher than those of larvae fed on young coconuts. The relative consumption rate of larvae fed on artificial diets was significantly lower than that of larvae fed on young coconuts. T. rufivena showed no significant degradation in ability to propagate after being reared on the artificial diet for five successive generations. These results indicated that two artificial diets are suitable for mass rearing of T. rufivena.     

Effect of plant nutrition on aphid size,prey consumption,and life history characteristics of green lacewing

Plant quality can directly and indirectly affect the third trophic level. The predation by all the instars of green lacewing, Chrysoperla carnea （S.） （Neuroptera： Chrysopidae） on the cereal aphids, Rhopalosiphum padi （L.）, and Sitobion avenae （F.） at varying nitrogen fertilizer levels was calculated under laboratory conditions. Wheat plants were grown on four nitrogen fertilizer levels and aphids were fed on these plants and subsequently offered as food to the C. carnea. Aphid densities of 10, 30, and 90 were offered to first, second, and third instar larvae of green lacewing. Increased nitrogen application improved nitrogen contents of the plants and also the body weight of cereal aphids feeding on them. Aphid consumption by green lacewings was reduced with the increase in nitrogen content in the host plants of aphids. Predation of both aphid species by first, second, and third instars larvae of C. carnea was highest on aphids reared on plants with the lowest rate of fertilization, suggesting a compensatory consumption to overcome reduced biomass （lower aphid size）. Total biomass devoured by C. carnea on all nitrogen fertilizer treatments was not statistically different. Additionally, the heavier host prey influenced by the plant nutrition had an effect on the life history characteristics of green lacewings. The larval duration, pupal weight, pupal duration, fecundity, and male and female longevity were significantly affected by the level of nitrogen fertilization to the aphid＇s host plants, except for pupal duration when fed on S. avenae. This study showed that quantity of prey supplied to the larvae affects the prey consumption and thereafter the life history characteristics of green lacewings.     

Facultative monophagy as a consequence of prior feeding experience: behavioral and physiological specialization in Colias philodice larvae

Summary Although newly-emerged Colias philodice readily accept Medicago sativa, Melilotus alba, and Coronilla varia, fifth instar larvae reared on any single plant species display a highly significant induced feeding preference for their rearing host. Forced host-switching reveals that fifth instar relative growth rate (RGR) on M. sativa and M. alba is significantly reduced by prior feeding on either alternative host. Moreover, regardless of rearing diet, switching to a novel host during the fifth instar results in reduced RGR, relative consumption rate (RCR), efficiency of conversion of digested food (ECD), and pupal weight. These results support the hypothesis that induction of feeding preference is an adaptive response that predisposes larvae to feed on the plant species they are most capable of utilizing for growth.     

Chitinolytic enzymes from Streptomyces albidoflavus expressed in tomato plants: effects on Trichoplusia ni

Tomato (Lycopersicon esculentum ) cultivars were transformed with genes that encode bacterial chitinolytic enzymes (i.e., endochitinase and chitobiosidase) from Streptomyces albidoflavus. Transgenic tomato plants producing these enzymes were found to have enhanced resistance to cabbage looper, Trichoplusia ni (Hübner) (Lepidoptera: Noctuidae), consistently reducing the growth rates of larvae. Mortality was significantly increased in two of three feeding trials. Ingestion of endochitinase and chitobiosidase not only affected development of larval T. ni from neonate to ultimate instar, but they also caused mortality and decreased insect weight when exposure began during the third instar. The results of this study provide some insight into the mode of action of the chitinolytic enzymes, by supporting the hypothesis that ingested chitinolytic enzymes damage the chitin component of the peritrophic envelope, leading to increased permeability. The size of marker molecules (FITC-dextrans) that permeated the peritrophic envelopes of T. ni feeding on transgenic plants were 50% larger than those permeating the peritrophic envelopes of T. ni feeding on the control plants. Further research is needed to more clearly identify the sites and modes of action of these chitinolytic enzymes, and the potential for synergy between these enzymes and pathogens, allelochemicals, and other environmental factors.     

A Comprehensive Assessment of the Effects of Bt Cotton on Coleomegilla maculata Demonstrates No Detrimental Effects by Cry1Ac and Cry2Ab

The ladybird beetle, Coleomegilla maculata (DeGeer), is a common and abundant predator in many cropping systems. Its larvae and adults are predaceous, feeding on aphids, thrips, lepidopteran larvae and plant tissues, such as pollen. Therefore, this species is exposed to insecticidal proteins expressed in insect-resistant, genetically engineered cotton expressing Cry proteins derived from Bacillus thuringiensis (Bt). A tritrophic bioassay was conduced to evaluate the potential impact of Cry2Ab- and Cry1Ac-expressing cotton on fitness parameters of C. maculata using Bt-susceptible and -resistant larvae of Trichoplusia ni as prey. Coleomegilla maculata survival, development time, adult weight and fecundity were not different when they were fed with resistant T. ni larvae reared on either Bt or control cotton. To ensure that C. maculata were not sensitive to the tested Cry toxins independent from the plant background and to add certainty to the hazard assessment, C. maculata larvae were fed artificial diet incorporated with Cry2Ab, Cry1Ac or both at >10 times higher concentrations than in cotton tissue. Artificial diet containing E-64 was included as a positive control. No differences were detected in any life-table parameters between Cry protein-containing diet treatments and the control diet. In contrast, larvae of C. maculata fed the E-64 could not develop to the pupal stage and the 7-d larval weight was significantly negatively affected. In both feeding assays, the stability and bioactivity of Cry proteins in the food sources were confirmed by ELISA and sensitive-insect bioassays. Our results show that C. maculata is not affected by Bt cotton and is not sensitive to Cry2Ab and Cry1Ac at concentrations exceeding the levels in Bt cotton, thus demonstrating that Bt cotton will pose a negligible risk to C. maculata. More importantly, this study demonstrates a comprehensive system for assessing the risk of genetically modified plants on non-target organisms.     

A proteinase inhibitor from Nicotiana alata inhibits the normal development of light-brown apple moth, Epiphyas postvittana in transgenic apple plants

Insecticidal proteins are a potential resource to enhance resistance to insect pests in transgenic plants. Here, we describe the generation and analysis of the apple cultivar ‘Royal Gala’ transgenic for Nicotiana alata (N. alata) proteinase inhibitor (PI) and the impact of this PI on the growth and development of the Epiphyas postvittiana (light-brown apple moth). A cDNA clone encoding a proteinase inhibitor precursor from N. alata (Na-PI) under the control of either a double 35S promoter or a promoter from a ribulose-1,5-bisphosphate carboxylase small sub-unit gene (rbcS-E9 promoter) was stably incorporated into ‘Royal Gala’ apple using Agrobacterium-mediated transformation. A 40.3 kDa Na-PI precursor protein was expressed and correctly processed into 6-kDa proteinase inhibitors in the leaves of transgenic apple lines. The 6-kDa polypeptides accumulated to levels of 0.05 and 0.1% of the total soluble protein under the control of the rbc-E9 promoter and the double 35S promoter, respectively. Light-brown apple moth larvae fed with apple leaves expressing Na-PI had significantly reduced body weight after 7 days of feeding and female pupae were 19–28% smaller than controls. In addition, morphological changes such as pupal cases attached to the wing, deformed wings, deformed body shape, and pupal cases and curled wings attached to a deformed body were observed in adults that developed from larvae fed with apple leaves expressing Na-PI, when compared to larvae fed with the non-transformed apple leaves.     

Larval feeding behaviour affects the impact of staminate flower production on the suitability of balsam fir trees for spruce budworm

Laboratory rearing of spruce budworm, Choristoneura fumiferana, in conjunction with field rearing indicated that the feeding behaviour of the larvae, which is affected by the insect population density, significantly influenced the impact of balsam fir, Abies balsamea, staminate flowering on spruce budworm biology. At low budworm density, the production of pollen in the midcrown of host trees reduced the insect development time by 5 days without affecting pupal weight, fecundity and survival. However, at high budworm density, the small amount of current-year foliage produced by flowering branches forced old larvae (sixth instar) either to feed on 1-year-old foliage (backfeeding) or to move from the midcrown to the lower crown section where staminate flowers are absent and more current-year foliage is available. When old larvae fed on old foliage, they exhibited reduced pupal weight and fecundity without losing the advange in development time that they obtained from feeding on pollen during their early stages of development. On the other hand, when old larvae moved to the lower crown section, they avoided the negative effects of backfeeding but lost the advantage in development time that was gained from feeding on pollen. Results from this study indicated that the production of staminate flowers by balsam fir trees could have opposite effects on spruce budworm population dynamics depending upon the insect population density when flowering occurs.     

Impact of non‐pathogenic bacteria on insect disease resistance: importance of ecological context

1. The aerial surface of plants is a habitat for large and diverse microbial communities; termed the phyllosphere. These microbes are unavoidably consumed by herbivores, and while the entomopathogens are well studied, the impact of non‐pathogenic bacteria on herbivore life history is less clear. 2. Previous work has suggested that consumption of non‐entomopathogenic bacteria induces a costly immune response that might decrease the risk of infection. However, we hypothesised that insect herbivores should be selective in how they respond to commonly encountered non‐pathogenic bacteria on their host plants to avoid unnecessary and costly immune responses. 3. An ecologically realistic scenario was used in which we fed cabbage looper, Trichoplusia ni Hübner, larvae on cabbage or cucumber leaves treated with the common non‐entomopathogenic phyllosphere bacteria, Pseudomonas fluorescens and P. syringae. Their constitutive immunity and resistance to a pathogenic bacterium (Bacillus thuringiensis; Bt) and a baculovirus (T. ni single nucleopolyhedrovirus) were then examined. 4. While feeding on bacteria‐treated leaves reduced the growth rate and condition of T. ni, there was no effect on immunity (haemolymph antibacterial and phenoloxidase activities and haemocyte numbers). Phyllosphere bacteria weakly affected the resistance of T. ni to Bt but the direction of this effect was concentration dependent; resistance to the virus was unaffected. Host plant had an impact, with cucumber‐fed larvae being more susceptible to Bt. 5. The lack of evidence for a costly immune response to non‐entomopathogenic bacteria suggests that T. ni are probably adapted to consuming common phyllosphere bacteria, and highlights the importance of the evolutionary history of participants in multi‐trophic interactions.     

Effects of natural and synthetic neuroactive substances on the growth and feeding of cabbage looper, Trichoplusia ni

In this study we investigated the effects of two naturally occurring beta-carboline alkaloids and two synthetic tricyclic antidepressants on the growth and food consumption of fifth instar larvae of the cabbage looper, Trichoplusia ni Hübner (Lepidoptera: Noctuidae). In artificial diets at high concentrations (3,000 ppm), harmane, amitriptyline, and imipramine reduce growth and feeding; harmane reduced feeding consistently at a lower concentration (200 ppm). In animals other than insects, beta-carboline alkaloids inhibit monoamine oxidase (MAO) activity and thus affect rates of disposition of serotonin and other monoamine neurotransmitters. Because brain serotonin levels are associated with variation in rates of carbohydrate and protein intake in insects, the effects of beta-carboline alkaloid ingestion on dietary self-selection behavior were examined. Choosing between diets lacking carbohydrate but containing protein and diets lacking protein but containing carbohydrate, larvae consumed a greater proportion of diet containing protein but lacking carbohydrate in the presence of harmane than in its absence. These results are consistent with beta-carboline alkaloid-mediated persistence of serotonin in the brain due to MAO inhibition. Alternatively, these results could reflect alkaloid-mediated peripheral inhibition of sucrose taste receptors influencing ingestive behaviors. That beta-carboline alkaloid ingestion is associated with changes in feeding behavior is consistent with a possible defensive role for these compounds in plant foliage.     

Effects of rutin-fed caterpillars on an invertebrate predator depend on temperature

Summary A factorial experiment examined the effects of varying concentrations of the allelochemical rutin in caterpillars and the length of time the caterpillars had fed on the behavioral interactions of predatory stinkbugs (Podisus maculiventris) and their prey (Manduca sexta). Diet had no significant effect on defensive behavior of the caterpillars. The length of time that the caterpillars had fed (1 vs. 24 h) only influenced the frequency of caterpillars knocking the attacking stinkbugs away, with caterpillars knocking the stinkbugs away more often after 24 h of feeding. A second experiment tested the effects of diet (prey fed various concentrations of rutin), temperature (18° C and 28° C) and gender on consumption and growth parameters of fifth instar stinkbugs. At the cooler temperature, the bugs ate more, gained more weight but took twice as long to complete the stadium and consequently had reduced relative consumption and relative growth rates. Diet had no significant effect on biomass gained or stadium duration, but rutin-fed caterpillars did depress the stinkbugs' relative consumption rates. The effect of food quality on relative growth rate (RGR) was temperature dependent; rutin had no significant effect at the cooler temperature, but a high dose of rutin reduced RGR at the warmer temperature. Rutin had a greater negative impact on the females than the males. The effect of rutin on these predators was different than the effect on their prey (this study compared to Stamp (1990, 1992)): the negative effects of rutin seem to impact on the stinkbug's growth rather than on molting.     

Feeding of fall armyworm,Spodoptera frugiperda,on Bt transgenic cotton and its isoline

Studies on insect food intake and utilization are important for determining the degree of insect/plant association and host species’ resistance, and also for helping design pest management programs by providing estimates of potential economic losses, techniques for mass breeding of insects, and identifying physiological differences between species. We studied the feeding and development of fall armyworm, Spodoptera frugiperda (JE Smith) (Lepidoptera: Noctuidae), on transgenic (Bt) and non‐transgenic (non‐Bt) cotton. The larvae of S. frugiperda fed on Bt cotton had a longer development period (23.0 days) than those fed on non‐Bt cotton (20.2 days). Survivorship of S. frugiperda larvae fed on Bt cotton (74.1%) was lower than that of larvae fed on non‐Bt cotton (96.7%). Pupal weight of larvae fed on Bt cotton (0.042 g) was lower than that of larvae fed on non‐Bt cotton (0.061 g). The cotton cultivar significantly affected food intake, feces production, metabolization, and food assimilation by S. frugiperda larvae. However, it did not affect their weight gain. Intake of Bt‐cotton leaf (0.53 g dry weight) per S. frugiperda larva was lower than the intake of non‐Bt‐cotton leaf (0.61 g dry weight). Larvae fed on Bt‐cotton leaves produced less feces (0.25 g dry weight) than those fed on non‐Bt‐cotton leaves (0.37 g dry weight). Weight gain per S. frugiperda larva fed on Bt‐cotton leaves (0.058 g dry weight) was similar to the weight gain for larvae fed on non‐Bt‐cotton leaves (0.056 g dry weight). The cotton cultivar significantly affected the relative growth, consumption, and metabolic rates, as well as other nutritional indices: the figures were lower for larvae fed on Bt‐cotton leaves than for larvae fed on non‐transgenic cotton leaves.     

Effect of food plant switching by a herbivore on its parasitoid: Cotesia melanoscela development in Lymantria dispar exposed to reciprocal dietary crosses

1. Host plant switching by dispersing early instar lepidopterans could have implications for parasitoid performance, but this possibility has not been evaluated thoroughly. 2. The relative growth rates of Lymantria dispar parasitized by Cotesia melanoscela, and the weight of larvae at the time of parasitoid emergence, were affected most by the second larval food plant consumed. 3. The relative growth rates, pupal weights, weight of larva at the time of parasitoid emergence, and development times of L. dispar were affected significantly by the second larval food plant consumed. 4. Development time and size of Cotesia melanoscela were affected most by the second larval food plant consumed. 5. Parasitoid performance was affected most by the larval host’s relative growth rate and the final weight of the host larva at the time of parasitoid emergence. 6. Host plant switching affected the weight of L. dispar larvae at the time of parasitoid emergence, but the effect of switching per se was not a significant factor in C. melanoscela size or development. 7. Lymantria dispar larvae that fed on Populus as their second host outperformed larvae that fed ultimately on Acer. 8. Parasitoids yielded from L. dispar larvae that fed ultimately on Populus outperformed parasitoids yielded from larvae that fed ultimately on Acer. 9. Per cent mortality of L. dispar due to parasitism and percentage adult C. melanoscela emergence were highest in parasitized larvae fed Populus, poor in hosts fed Acer, and intermediate in switching larvae.     

Decreased Response to Feeding Deterrents Following Prolonged Exposure in the Larvae of a Generalist Herbivore, Trichoplusia ni (Lepidoptera: Noctuidae)

We investigated the role of experience with several antifeedants on the feeding behavior of a generalist herbivore, Trichoplusia ni. Second-, third-, and fifth-instar larvae of T. ni were examined for their feeding responses to plant extracts (Melia volkensii, Origanum vulgare) and individual plant allelochemicals (cymarin, digitoxin, xanthotoxin, toosendanin, and thymol), after being exposed to them continually beginning as neonates. All tested instars of T. ni were capable of showing a decreased antifeedant response following prolonged exposure to most of the antifeedants tested compared with their naive conspecifics. Cardenolides (digitoxin and cymarin) were the exceptions. The response to oregano was affected as a result of previous exposure to different concentrations of oregano, unlike M. volkensii, leading us to conclude that T. ni sensitivity varies between stimuli and cannot be generalized. To demonstrate that decreased deterrence following prolonged exposure to M. volkensii was the result of learned habituation, three aversive stimuli were used. A high concentration of the particular antifeedant, xanthotoxin, acted as a noxious stimulus and dishabituated (reversed) the decrement in the antifeedant response to M. volkensii. Cold shock or CO₂ was marginally effective in dishabituating the response. The fact that the decrease in antifeedant response can be dishabituated has implications for pest management.     

The importance of honeydew as food for larvae of Chrysoperla carnea in the presence of aphids

Larvae of the common green lacewing Chrysoperla carnea are predacious and feed on a wide range of small, soft‐bodied arthropods. In addition to their feeding on prey arthropods to cover their nutritional requirements for growth and development, the consumption of non‐prey foods such as honeydew has been reported. It is commonly believed that these food supplements are primarily exploited by the larvae when prey is scarce or of low nutritional quality. Here, we assess whether C. carnea larvae also use honeydew when high‐quality aphid prey are readily available. In a choice experiment, the feeding behaviour of C. carnea larvae was observed in the presence of both aphids and honeydew. The larvae were starved, aphid‐fed, or honeydew‐fed prior to the experiment. The time spent feeding on honeydew compared with feeding on aphids was highest for starved larvae and lowest for honeydew‐fed larvae. Among the three treatments, the aphid‐fed larvae spent the most time resting and the least time searching. In an additional experiment food intake was assessed in terms of weight change when larvae were provided with an ad libitum supply of either aphids or honeydew. Larvae yielded a significant lower relative weight increase on honeydew compared with aphids. The reduced weight increase on honeydew was compensated when larvae were subsequently provided with aphids, but not when honeydew was provided again. This study showed that (i) prior honeydew feeding reduces overall aphid consumption, and (ii) larvae do consume honeydew even after they have been given ad libitum access to aphids. The fact that larvae of C. carnea still use honeydew as a food source in the presence of suitable prey underlines the importance of carbohydrates as foods.