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Honeybee toxicology is complex because effects on individual bees are modulated by social interactions between colony members. In the present study, we applied high doses of the insect growth regulator fenoxycarb to honeybee colonies to elucidate a possible interplay of individually- and colony-mediated effects regarding honey bee toxicology. Additionally, possible effects of the solvent dimethyl sulfoxide (DMSO) were assessed. We conducted studies on egg hatching and brood development to assess brood care by nurse bees as well as queen viability. Egg hatching was determined by the eclosion rate of larvae from eggs originating from colonies (i) treated with sugar syrup only, (ii) treated with sugar syrup containing DMSO and (iii) treated with sugar syrup containing fenoxycarb (dissolved in DMSO). To evaluate brood development, combs with freshly laid eggs were reciprocally transferred between colonies, and development of brood was examined in the recipient hive. Brood reared inside DMSO- and fenoxycarb-treated colonies as well as brood from DMSO- and from fenoxycarb-exposed queens showed higher mortality than brood not exposed to the chemicals. No differences were found in egg hatching among the treatments, but there was a higher variability of eclosion rates after queens were exposed to fenoxycarb. We also observed queen loss and absconding of whole colonies. Based on our results we infer that fenoxycarb has queen- as well as nurse bee-mediated effects on brood quality and development which can lead to the queen's death. There also is an effect of DMSO on the nurse bees' performance that could disturb the colony's equilibrium, at least for a delimited timespan.

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Abstract. All organisms have to cope with spatial and temporal heterogeneity of the environment. At short temporal and small spatial scales, organisms may respond by behavioural or physiological mechanisms. To test for physiological adjustments to variation in host quality among tree individuals within a host species, we performed a transfer experiment in a climate chamber using larvae of the polyphagous gypsy moth (Lymantria dispar). We reared larvae for two weeks on leaves of one of three Quercus robur individuals. We found differences in the growth rate of larvae across the host individuals, which indicate that the oak individuals differed in their quality. Furthermore, families of larvae varied in their growth rate and there was variation among the families of gypsy moth larvae in response to leaves from the different oak individuals. After two weeks we offered larvae either leaves of the same or a different individual of the three oaks. We found no effect of transferring larvae to a different tree individual. The results thus do not support the idea of physiological adjustment of a generalist insect herbivore to variation in leaf quality among host individuals.