The influence of insecticide residues on primary parasitoid and hyperparasitoid foraging behaviour in the laboratory

The behaviour of Aphidius rhopalosiphi DeStefani-Perez (Hymenoptera: Braconidae) was recorded in laboratory bioassays in the presence and absence of both residues of honeydew from the English grain aphid, Sitobion avenae (F.) and the pyrethroid insecticide, deltamethrin. Insecticide concentrations ranged from the field recommended dose rate (6.25 g ai/ha in 2001 water) to 1/16th of field rate. Parasitoids responded strongly to patches of honeydew on filter papers, however the addition of increasing concentrations of deltamethrin caused increasingly early departure from the honeydew-treated areas. Parasitoids pre-exposed to field concentration residues for between 1 and 20 min showed shorter retention times and abnormal types of behaviour on honeydew-treated patches compared to control wasps. Recovery of normal behaviour patterns occurred over a 12 h period away from the insecticide source. Further laboratory studies examined the foraging of A. rhopalosiphi and one of its associated hyperparasitoids, Dendrocerus carpenteri (Curtis), on mature wheat plants treated with an artificial honeydew solution and deltamethrin. Wasps exposed to deltamethrin residues were observed to spend shorter visit times, to groom more frequently and to rest less frequently than those on insecticide-free plants. Differences were found between the distribution of parasitoids on insecticide-treated and untreated plants, with D. carpenteri showing greater movement down insecticide-treated plants accompanied with an increase in time spent on abaxial leaf surfaces compared to A. rhopalosiphi. The results are discussed in terms of the repellency of deltamethrin and the implications for integrated pest management of differing sub-lethal insecticide effects on primary parasitoid and hyperparasitoid behaviour.