Bumble bees show an induced preference for flowers when primed with caffeinated nectar and a target floral odor.

Caffeine is a widely occurring plant defense chemical1,2 that occurs in the nectar of some plants, e.g., Coffea or Citrus spp., where it may influence pollinator behavior to enhance pollination.3,4 Honey bees fed caffeine form longer lasting olfactory memory associations,5 which could give plants with caffeinated nectar an adaptive advantage by inducing more visits to flowers. Caffeinated free-flying bees show enhanced learning performance6 and are more likely to revisit a caffeinated target feeder or artificial flower,7-9 although it is not clear whether improved memory of the target cues or the perception of caffeine as a reward is the cause. Here, we show that inexperienced bumble bees (Bombus terrestris) locate new food sources emitting a learned floral odor more consistently if they have been fed caffeine. In laboratory arena tests, we fed bees a caffeinated food alongside a floral odor blend (priming) and then used robotic experimental flowers10 to disentangle the effects of caffeine improving memory for learned food-associated cues versus caffeine as a reward. Inexperienced bees primed with caffeine made more initial visits to target robotic flowers emitting the target odor compared to control bees or those primed with odor alone. Caffeine-primed bees tended to improve their floral handling time faster. Although the effects of caffeine were short lived, we show that food-locating behaviors in free-flying bumble bees can be enhanced by caffeine provided in the nest. Consequently, there is potential to redesign commercial colonies to enhance bees' forage focus or even bias bees to forage on a specific crop.

Impact of a tarsonemid prey mite and its fungal diet on the reproductive performance of a predatory mite.

Phytoseiid predatory mites are the most important group of biocontrol agents currently used in protected cultivations worldwide. The possibility to produce these predators at high densities on factitious prey mites is a crucial factor for their success. Commonly used factitious prey mites comprise mainly species belonging to the cohort of Astigmatina. In the present study, we investigated the potential of tarsonemid prey mites as a food source for the spider mite predator Neoseiulus californicus (McGregor) (Acari: Phytoseiidae). The oviposition of N. californicus on mixed stages of Tarsonemus fusarii Cooreman (Acari: Tarsonemidae) was similar to that on its natural prey, the two-spotted spider mite Tetranychus urticae Koch (Acari: Tetranychidae). As most tarsonemids are specialized fungus-feeders, we tested the effect of different fungal species on the growth of T. fusarii. Subsequently, we analysed the impact on the fungal growing medium on the oviposition of N. californicus. The fungal growing medium of T. fusarii had a significant negative effect on the reproductive output of the predatory mite. When T. fusarii was separated from the rearing medium, these detrimental effects were not observed. The present study shows the potential of using tarsonemid prey mites in the production of phytoseiid predatory mites.

Aphidophagous hoverflies reduce foxglove aphid infestations and improve seed set and fruit yield in sweet pepper.

BACKGROUND: Larvae of many hoverfly species prey upon aphids, whereas the adults, by relying on nectar and pollen, contribute to the pollination of many plant species. Despite their great potential for pest control and pollination, important gaps still exist regarding the efficacy of hoverflies in regulating infestations of major aphid pests in augmentative biological control programs. Here, we tested the potential of the commercially available hoverflies Eupeodes corollae and Sphaerophoria rueppellii to regulate populations of the foxglove aphid Aulacorthum solani in sweet pepper. RESULTS: In a semi-field experiment, aphid numbers were 93.2% and 78.4% lower in the E. corollae and S. rueppellii treatments, respectively, compared to the control. Fruit yield was increased by 390% and 361% and seed set by 395% and 399% for E. corollae and S. rueppellii. In a separate laboratory trial, we found that under conditions of limited prey, hoverfly larvae did not complete development, but that larvae of S. rueppellii survived significantly longer than larvae of E. corollae. CONCLUSION: We have shown for the first time that E. corollae and S. rueppellii can reduce infestations of foxglove aphid in sweet pepper. The limited amount of prey, related to the small size of the A. solani colonies, means that hoverfly larvae were often not able to complete development. In practice, repeated releases of hoverflies, possibly in combination with other natural enemies, might be used to achieve effective suppression of A. solani infestations. © 2021 Society of Chemical Industry.

Bottom-up Effects on Tri-trophic Interactions: Plant Fertilization Enhances the Fitness of a Primary Parasitoid Mediated by Its Herbivore Host.

Plants play a pivotal role in interactions involving herbivores and their natural enemies. Variation in plant primary and secondary metabolites not only affects herbivores but, directly and indirectly, also their natural enemies. Here, we used a commercial NPK fertilizer to test the impact of three fertilizer, namely 50, 100, and 200 ppm nitrogen, and one control (i.e., water) treatments, on the weight of the nymphs of the whitefly Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae). Subsequently, the whitefly parasitoid Eretmocerus mundus Mercet (Hymenoptera: Aphelinidae) was reared on the different groups of whitefly nymphs and upon parasitoid emergence, the number of oocytes was determined as a measure of reproductive capacity. Trials were done on tomato and tobacco plants. The level of nitrogen concentration in tobacco leaves was directly correlated with the fertilizer applications, thus confirming the effect of our fertilizer treatments. Both in tomato and tobacco plants, healthy as well as parasitized whitefly nymphs, were heaviest in the 200 ppm nitrogen treatment. The highest number of oocytes per female parasitoid was recorded in the 200 ppm nitrogen treatment in tomato (31% more oocytes as compared with the control) and in the 100 and 200 ppm nitrogen treatments in tobacco (200% more oocytes). We suggest that the increase in oocytes was the result of the enhanced size (food quantity) and/or nutritional quality of the whitefly host. The practical implications of these results for the mass rearing of whitefly parasitoids and for biological pest control are discussed.

Augmentative releases of the soil predatory mite Gaeolaelaps aculeifer reduce fruit damage caused by an invasive thrips in Mediterranean citrus.

BACKGROUND: Soil-dwelling predatory mites of the family Laelapidae are augmentatively released for the biological control of several pests with an edaphic phase in numerous greenhouse crops. Yet, there is no information about the potential of releasing these predators to control pests in open field crops. We tested, during two consecutive years, the potential of augmentative releases of Gaeolaelaps aculeifer, alone or in combination with coco fiber discs as mulch, to reduce the damage caused on citrus fruits by the invasive thrips Pezothrips kellyanus in Mediterranean citrus. In a separate trial, we also compared different mulch types (coco fiber discs, rice husks or a mixture of sawdust and wheat bran) for their potential to support the establishment and population development of the predatory mites after their release. RESULTS: The percentage of unmarketable fruits caused by P. kellyanus was significantly reduced in the plots where G. aculeifer was released. The addition of coco fiber discs did not reduce further the percentage of unmarketable fruits. Sawdust + bran mulch was the most effective in preserving immature and adult predatory mite population after their release. CONCLUSION: Augmentative releases of G. aculeifer have the potential to reduce fruit damage caused by P. kellyanus in citrus. © 2020 Society of Chemical Industry.

Optimizing aphid biocontrol with the predator Aphidoletes aphidimyza, based on biology and ecology.

Aphidoletes aphidimyza is one of the most important predators used in the augmentative biological control of aphids, key pests of many crops worldwide. Adult females are very efficient in locating aphid infestations over a relatively long range, up to 45 m, and deposit eggs near or within aphid colonies. The predatory larvae are aphid generalists preying on several agriculturally important aphid species. The successful use of this biocontrol agent in agricultural systems depends on several biotic and abiotic factors. Among biotic factors, aphid species, plant structure, interspecific competition and intraguild predation may significantly impact the predator´s population dynamics. Key abiotic conditions include day lengths (above a critical threshold to prevent diapause), availability of mating sites in the crop, temperature (above 15 °C to enable egg laying), air relative humidity (above 70%) and availability of pupation sites. Although several successes have been reported in open field crops with naturally occurring or released populations, commercial releases are primarily used in protected crops. Optimized emergence boxes combining provisioning of food sources for the adults, integration with the technological advances that occurred in the greenhouse environment lately, insights into the nutritional ecology in open field crops and exploration of the genetic variability are proposed as future directions to improve adoption and efficacy of A. aphidimyza in crop protection. © 2018 Society of Chemical Industry.

The Quality of Nonprey Food Affects Cannibalism, Intraguild Predation, and Hyperpredation in Two Species of Phytoseiid Mites.

Generalist arthropod predators not only prey on herbivores but also may engage in competitive interactions by attacking and consuming conspecifics (cannibalism) or other predators (intraguild predation [IGP] and hyperpredation). These types of interactions are quite common among predators used in biological control. Although there is evidence that nonprey food relaxes cannibalism and IGP, there is little information regarding the impact of the quality of the nonprey food. Herein, we examined how pollen of different nutritional quality (pine, narrow-leaf cattail, or apple) impacted 1) the cannibalism by females of Euseius stipulatus (Athias-Henriot) (Acari: Phytoseiidae) on conspecific larvae, 2) the reciprocal predation between gravid females of E. stipulatus or Iphiseius degenerans (Berlese) (Acari: Phytoseiidae) and heterospecific larvae, and 3) the predation of E. stipulatus on the eggs of the aphid predator Aphidoletes aphidimyza (Rondani) (Diptera: Cecidomyiidae). E. stipulatus cannibalism was significantly reduced in the cattail pollen treatment, whereas in the pine pollen it did not significantly differ from control (no food). Predation between I. degenerans and E. stipulatus was significantly reduced in the cattail pollen treatment as compared to the control treatment. Finally, predation of E. stipulatus on A. aphidimyza eggs was significantly reduced when cattail or apple pollen was provided compared to the pine pollen or control treatments. These results suggest that cattail or apple pollen is suitable for mitigating negative interactions among generalist predatory mites used in biological control.

Association between ants (Hymenoptera: Formicidae) and the vine mealybug (Hemiptera: Pseudococcidae) in table-grape vineyards in Eastern Spain.

BACKGROUND: The vine mealybug, Planococcus ficus (Signoret) (Hemiptera: Pseudococcidae) is a key pest of grapevine in the Mediterranean Basin. Some honeydew collecting ant species are known to increase mealybug populations in other grape-growing regions. However, there is scarce information on either the ant species present in Mediterranean vineyards or their impact on mealybugs. We conducted a study in four commercial vineyards in Eastern Spain in order to i) identify the ant species foraging on the vine canopies, ii) study the association among ant activity, vine mealybug abundance and fruit damage, and iii) test a novel method for ant management, distracting ants from guarding vine mealybugs by providing sugar dispensers. RESULTS: We recorded three ant species native to the Mediterranean foraging on the vine canopies: Lasius grandis (Forel), Pheidole pallidula (Nylander) and Plagiolepis schmitzii (Forel). The mean percentage of damaged fruits per vine was positively correlated with the number of vine mealybugs captured in traps placed at the trunk. We detected a positive but weak relationship between ant activity, vine mealybug abundance and fruit damage. The provisioning of sugar dispensers reduced the number of ants foraging on the vines by 23.4% although this reduction was not statistically significant. Vine mealybug abundance was significantly reduced (72%) after sugar provisioning. CONCLUSION: Our results suggest that the ant species native to vineyards in eastern Spain induce population increases of the vine mealybug. Moreover, the provisioning of sugars can be a valuable tool for ant management and mealybug control. © 2017 Society of Chemical Industry.

Multiple resource supplements synergistically enhance predatory mite populations.

Many plants offer food rewards such as extrafloral nectar and food bodies, which have been shown to attract and retain entomophagous arthropods. In addition to food rewards, plants may possess structures that serve as shelter and/or oviposition sites for beneficial arthropods, so-called domatia. Acarodomatia are commonly used by beneficial mites for oviposition and protection from intraguild predators and adverse climatic conditions (drought). While in nature these food and shelter traits often occur in combination, they have been largely studied in isolation and we know little about how these traits interact, i.e., whether they act independently, antagonistically or synergistically. In the present study, we used citrus seedlings to test the impact of provisioning fibers (as a proxy for acarodomatia), as well as two different categories of food rewards (pollen and sugars) on oviposition and population development of phytoseiid mites. The highest oviposition and abundance of predatory mites was obtained in the treatment where the three resources were offered in combination. The combined impact of the three resources when provided jointly was up to five times higher than the summed impacts of each resource provided individually, thus providing evidence for a three-way synergy between the fibers, pollen and sugars. From an ecological point of view, our results demonstrate that combining multiple indirect defensive traits can strongly enhance the impact on the mutualistic arthropods. Differences in resource provisioning strategies in plant-phytoseiid and plant-ant mutualisms are being discussed. The presented results are of particular importance for our understanding of the functioning of defensive plant-arthropod mutualisms, as well as for the use of predatory mites in conservation- or inundative biological control.

Parasitoid nutritional ecology in a community context: the importance of honeydew and implications for biological control.

One focus of conservation biological control studies has been to improve the nutritional state and fitness of parasitoids by adding nectar and artificial sugars to agroecosystems. This approach has largely overlooked the presence of honeydew, which is likely the primary carbohydrate source available to parasitoids in many agroecosystems. Over the last decade, it has been demonstrated that parasitoids often utilize this sugar source and there is evidence that honeydew can indirectly impact the population dynamics of herbivores through its nutritional value for parasitoids. The consumption of honeydew by parasitoids can shape direct and indirect interactions with other arthropods. The strength of these effects will depend on: first, parasitoid biology, second, the presence of other sugar sources (mainly nectar), third, the quality and quantity of the honeydew, and fourth, the presence and competitive strength of other honeydew consumers such as ants. The combination of these four factors is expected to result in distinct scenarios that should be analyzed for each agroecosystem. This analysis can reveal opportunities to increase the biocontrol services provided by parasitoids. Moreover, honeydew can be a resource-rich habitat for insect pathogens; or contain plant secondary chemicals sequestered by hemipterans or systemic insecticides toxic for the parasitoid. Their presence and effect on parasitoid fitness will need to be addressed in future research.

Comparison of Peach Cultivars for Provision of Extrafloral Nectar Resources to Harmonia axyridis (Coleoptera: Coccinellidae).

Incorporating nonprey sugar resources into apple orchards is a potential means of enhancing biological control services, but little is known about the impacts of extrafloral nectars on aphidophagous coccinellids. We explored peach Prunus persica (L.) Batsch extrafloral nectar as a supplemental resource for Harmonia axyridis (Pallas), a key aphid predator in the mid-Atlantic United States. Extrafloral nectar quantity, temporal production, and carbohydrate profile were assessed for four peach cultivars in orchard and greenhouse culture. Seasonal densities of H. axyridis visiting extrafloral nectaries were estimated, and the propensity of beetles to feed upon extrafloral nectar was compared by cultivar in the laboratory. We also compared survival of newly eclosed adult pairs that were starved or fed aphids with or without extrafloral nectar. Peach extrafloral nectar contained six carbohydrates, with sucrose dominant for all cultivars, but extrafloral nectar production varied significantly by cultivar and collection date, with 'Lovell' yielding higher average seasonal volume than the other cultivars. Harmonia axyridis continuously foraged on peach trees lacking prey, and beetle abundance was positively correlated with the number of leaves actively producing extrafloral nectar. In laboratory assays, newly emerged adult beetles preferentially selected and consumed extrafloral nectar of Lovell peach shoots. Furthermore, when prey were initially unavailable to adult H. axyridis, the beetles were sustained by extrafloral nectar and experienced longer survival compared with beetles without the supplemental resource. Collectively, these results suggest that peach extrafloral nectar is a beneficial resource that could potentially sustain H. axyridis in orchards when prey are scarce.

Predation of the Peach Aphid Myzus persicae by the mirid Predator Macrolophus pygmaeus on Sweet Peppers: Effect of Prey and Predator Density.

Integrated Pest Management strategies are widely implemented in sweet peppers. Aphid biological control on sweet pepers includes curative applications of parasitoids and generalist predators, but with limited efficiency. Macrolophus pygmaeus is a zoophytophagous predator which has been reported to predate on aphids, but has traditionally been used to control other pests, including whiteflies. In this work, we evaluate the effectiveness of M. pygmaeus in controlling Myzus persicae (Homoptera: Aphididae) by testing different combinations of aphid and predator densities in cage-experiments under greenhouse conditions. The impact of the presence of an alternative factitious prey (E. kuehniella eggs) was also investigated. Macrolophus pygmaeus, at densities of four individuals/plant, caused rapid decline of newly established aphid populations. When aphid infestations were heavy, the mirid bug reduced the aphid numbers but did not fully eradicate aphid populations. The availability of a factitious prey did not influence M. pygmaeus predation on aphids. Based on our data, preventive application of M. pygmaeus, along with a supplementary food source , is recommended to control early infestations of aphids.

Aphid honeydew quality as a food source for parasitoids is maintained in Bt cotton.

Bt-transgenic cotton has proven to be highly efficient in controlling key lepidopteran pests. One concern with the deployment of Bt cotton varieties is the potential proliferation of non-target pests. We previously showed that Bt cotton contained lower concentrations of insecticidal terpenoids as a result of reduced caterpillar damage, which benefited the aphid Aphis gossypii. It is thus important that non-target herbivores are under biological control in Bt cotton fields. The induction or lack of induction of terpenoids could also influence the quality of aphid honeydew, an important food source for beneficial insects. We therefore screened A. gossypii honeydew for cotton terpenoids, that are induced by caterpillars but not the aphids. We then tested the influence of induced insect-resistance of cotton on honeydew nutritional quality for the aphid parasitoid Lysiphlebus testaceipes and the whitefly parasitoid Eretmocerus eremicus. We detected the cotton terpenoids gossypol and hemigossypolone in A. gossypii honeydew. Although a feeding assay demonstrated that gossypol reduced the longevity of both parasitoid species in a non-linear, dose-dependent manner, the honeydew was capable of sustaining parasitoid longevity and reproduction. The level of caterpillar damage to Bt and non-Bt cotton had no impact on the quality of honeydew for the parasitoids.These results indicate that the nutritional quality of honeydew is maintained in Bt cotton and is not influenced by induced insect resistance.

Egg load dynamics and the risk of egg and time limitation experienced by an aphid parasitoid in the field.

Insect parasitoids and herbivores must balance the risk of egg limitation and time limitation in order to maximize reproductive success. Egg and time limitation are mediated by oviposition and egg maturation rates as well as by starvation risk and other determinants of adult lifespan. Here, we assessed egg load and nutritional state in the soybean aphid parasitoid Binodoxys communis under field conditions to estimate its risk of becoming either egg- or time-limited. The majority of female B. communis showed no signs of egg limitation. Experimental field manipulations of B. communis females suggested that an average of 4-8 eggs were matured per hour over the course of a day. Regardless, egg loads remained constant over the course of the day at approximately 80 eggs, suggesting that egg maturation compensates for oviposition. This is the first case of such "egg load buffering" documented for a parasitoid in the field. Despite this buffering, egg loads dropped slightly with increasing host (aphid) density. This suggests that egg limitation could occur at very high host densities as experienced in outbreak years in some locations in the Midwestern USA. Biochemical analyses of sugar profiles showed that parasitoids fed upon sugar in the field at a remarkably high rate. Time limitation through starvation thus seems to be very low and aphid honeydew is most likely a source of dietary sugar for these parasitoids. This latter supposition is supported by the fact that body sugar levels increase with host (aphid) density. Together, these results suggest that fecundity of B. communis benefits from both dynamic egg maturation strategies and sugar-feeding.

Indirect multi-trophic interactions mediated by induced plant resistance: impact of caterpillar feeding on aphid parasitoids.

Cotton produces insecticidal terpenoids that are induced by tissue-feeding herbivores. Damage by Heliothis virescens caterpillars increases the terpenoid content, which reduces the abundance of aphids. This effect is not evident in Bt-transgenic cotton, which is resistant to H. virescens. We determined whether induction of terpenoids by caterpillars influences the host quality of Aphis gossypii for the parasitoid Lysiphlebus testaceipes and whether this interaction is influenced by Bt cotton. The exposure of parasitoids to terpenoids was determined by quantifying terpenoids in the aphids. We detected several terpenoids in aphids and found a positive relationship between their concentrations in plants and aphids. When L. testaceipes was allowed to parasitize aphids on Bt and non-Bt cotton that was infested or uninfested with H. virescens, fewer parasitoid mummies were found on infested non-Bt than on Bt cotton. Important parasitoid life-table parameters, however, were not influenced by induced resistance following H. virescens infestation, or the Bt trait. Our study provides an example of a tritrophic indirect interaction web, where organisms are indirectly linked through changes in plant metabolites.

Pest trade-offs in technology: reduced damage by caterpillars in Bt cotton benefits aphids.

The rapid adoption of genetically engineered (GE) plants that express insecticidal Cry proteins derived from Bacillus thuringiensis (Bt) has raised concerns about their potential impact on non-target organisms. This includes the possibility that non-target herbivores develop into pests. Although studies have now reported increased populations of non-target herbivores in Bt cotton, the underlying mechanisms are not fully understood. We propose that lack of herbivore-induced secondary metabolites in Bt cotton represents a mechanism that benefits non-target herbivores. We show that, because of effective suppression of Bt-sensitive lepidopteran herbivores, Bt cotton contains reduced levels of induced terpenoids. We also show that changes in the overall level of these defensive secondary metabolites are associated with improved performance of a Bt-insensitive herbivore, the cotton aphid, under glasshouse conditions. These effects, however, were not as clearly evident under field conditions as aphid populations were not correlated with the amount of terpenoids measured in the plants. Nevertheless, increased aphid numbers were visible in Bt cotton compared with non-Bt cotton on some sampling dates. Identification of this mechanism increases our understanding of how insect-resistant crops impact herbivore communities and helps underpin the sustainable use of GE varieties.

The effect of different dietary sugars and honey on longevity and fecundity in two hyperparasitoid wasps.

In nature adult insects, such as parasitic wasps or 'parasitoids' often depend on supplemental nutritional sources, such as sugars and other carbohydrates, to maximize their life-expectancy and reproductive potential. These food resources are commonly obtained from animal secretions or plant exudates, including honeydew, fruit juices and both floral and extra-floral nectar. In addition to exogenous sources of nutrition, adult parasitoids obtain endogenous sources from their hosts through 'host-feeding' behavior, whereby blood is imbibed from the host. Resources obtained from the host contain lipids, proteins and sugars that are assumed to enhance longevity and/or fecundity. Here we conducted an experiment exploring the effects of naturally occurring sugars on longevity and fecundity in the solitary hyperparasitoids, Lysibia nana and Gelis agilis. Although both species are closely related, L. nana does not host-feed whereas G. agilis does. In a separate experiment, we compared reproduction and longevity in G. agilis reared on either honey, a honey-sugar 'mimic', and glucose. Reproductive success and longevity in both hyperparasitoids varied significantly when fed on different sugars. However, only mannose- and water-fed wasps performed significantly more poorly than wasps fed on four other sugar types. G. agilis females fed honey produced twice as many progeny as those reared on the honey-sugar mimic or on glucose, whereas female longevity was only reduced on the mimic mixture. This result shows not only that host feeding influences reproductive success in G. agilis, but also that non-sugar constituents in honey do. The importance of non-sugar nutrients in honey on parasitoid reproduction is discussed.

Neonicotinoid pesticide reduces bumble bee colony growth and queen production.

Growing evidence for declines in bee populations has caused great concern because of the valuable ecosystem services they provide. Neonicotinoid insecticides have been implicated in these declines because they occur at trace levels in the nectar and pollen of crop plants. We exposed colonies of the bumble bee Bombus terrestris in the laboratory to field-realistic levels of the neonicotinoid imidacloprid, then allowed them to develop naturally under field conditions. Treated colonies had a significantly reduced growth rate and suffered an 85% reduction in production of new queens compared with control colonies. Given the scale of use of neonicotinoids, we suggest that they may be having a considerable negative impact on wild bumble bee populations across the developed world.

Characterizing indirect prey-quality mediated effects of a Bt crop on predatory larvae of the green lacewing, Chrysoperla carnea.

There is increasing evidence that insecticidal transgenic crops can indirectly cause detrimental effects on arthropod predators or parasitoids when they prey on or parasitize sublethally affected herbivores. Our studies revealed that Chrysoperla carnea is negatively affected when fed Bt-susceptible but not Cry1Ac-resistant Helicoverpa armigera larvae that had fed Bt-transgenic cotton expressing Cry1Ac. This despite the fact that the predators ingested 3.5 times more Cry1Ac when consuming the resistant caterpillars. In order to detect potential differences in the nutrient composition of prey larvae, we evaluated the glycogen and lipid content plus the sugar and free amino acid content and composition of caterpillars fed non-Bt and Bt cotton. The only change in susceptible H. armigera larvae attributable to Bt cotton feeding were changes in sugar concentration and composition. In case of the Cry1Ac-resistant H. armigera strain, feeding on Bt cotton resulted in a reduced glycogen content in the caterpillars. The predators, however, appeared to compensate for the reduced carbohydrate content of the prey by increasing biomass uptake which caused an excess intake of the other analyzed nutritional compounds. Our study clearly proves that nutritional prey-quality factors other then the Bt protein underlie the observed negative effects when C. carnea larvae are fed with Bt cotton-fed prey. Possible factors were an altered sugar composition or fitness costs associated with the excess intake of other nutrients.

Honeydew feeding in the solitary bee Osmia bicornis as affected by aphid species and nectar availability.

Like honey bees (Apis mellifera), non-Apis bees could exploit honeydew as a carbohydrate source. In addition to providing carbohydrates, this may expose them to potentially harmful plant products secreted in honeydew. However, knowledge on honeydew feeding by solitary bees is very scarce. Here we determine whether the polylectic solitary bee Osmia bicornis (=O. rufa) collects honeydew under semi-field conditions, and whether this is affected by aphid species and presence of floral nectar. Bees were provided with oilseed rape plants containing flowers and/or colonies of either Myzus persicae or Brevicoryne brassicae. We used the total sugar level of the bee crop as a measure of the individual's nutritional state and the oligosaccharide erlose as indicator for honeydew consumption. Erlose was present in honeydews from both aphid species, while absent in oilseed rape nectar, nor being synthesized by O. bicornis. When bees were confined to a single honeydew type as the only carbohydrate source, consumption of M. persicae honeydew was confirmed for 47% of the bees and consumption of B. brassicae honeydew for only 3%. Increased mortality in the latter treatment provided further evidence that B. brassicae honeydew is an unsuitable food source for O. bicornis. All bees that were given the choice between honeydew and floral nectar showed significantly increased total sugar levels. However, the fact that no erlose was detected in these bees indicates that honeydew was not consumed when suitable floral nectar was available. This study demonstrates that honeydew exploitation by O. bicornis is dependent on honeydew type and the presence of floral nectar.