EFFECTS OF HONEYDEW AND INSECTICIDE RESIDUES ON THE DISTRIBUTION OF FORAGING APHID PARASITOIDS UNDER GLASSHOUSE AND FIELD CONDITIONS

The opposing effects of attraction to host-derived kairomones and repe llency from the pyrethroid insecticide deltamethrin were investigated with aphid parasitoids from the genus Aphidius (Hymenoptera: Aphidiina e). The spatial distribution of female parasitoids was recorded in a s eries of experiments conducted in a small glasshouse containing wheat plants either infested with cereal aphids, Sitobion avenae (F.) (Homop tera: Aphididae), uninfested or treated with the recommended field con centration of deltamethrin. The number of parasitoids per plant were c ounted at 0.5 h, 1 h and then at one hourly intervals up to 8 h after release. Parasitoids showed a strong aggregation response to aphid-inf ested plants compared to adjacent uninfested plants. With the introduc tion of insecticide-treated plants around the aphid-infested plants, p arasitoids showed a greater tendency to disperse away, resulting in fe wer parasitoids on plants and significantly lower rates of aphid paras itism. The degree of aphid fall-off from plants was a good indicator o f parasitoid foraging activity. In field studies, using sticky traps t o measure the activity of parasitoids in plots sprayed with water, del tamethrin and/or an artificial honeydew solution, repellent properties were evident for up to 2 days after application. The attraction/arres tment stimuli associated with the honeydew solution were sufficient fo r parasitoids to continue searching insecticide-treated areas. The imp lications of these findings for parasitoids searching crops contaminat ed with aphid-derived kairomones and insecticides are discussed.