A space-efficient contact toxicity bioassay for minute Hymenoptera, used to test the effects of novel and conventional insecticides on the egg parasitoids Anaphes iole and Trichogramma pretiosum

We developed and tested anovel bioassay method for assessment of contactresidues of pesticides to minute Hymenoptera. This method maintained a plant-toxin-insectinterface representative of natural conditionsin the field or greenhouse, and wasspace-efficient. The procedure was useful instudies with both foliar residues and systemicuptake. Furthermore, the method was relativelystraightforward, easy to setup, andinexpensive. Tests with the egg parasitoidsAnaphes iole Girault (Hymenoptera:Mymaridae) and Trichogramma pretiosumRiley (Hymenoptera: Trichogrammatidae)confirmed that this method provided consistent,repeatable assessment of concentration-responserelationships for several insecticide classes. Other researchers studying pesticide effects onminute Hymenoptera might find this bioassaymethod helpful, especially in situations wherespace is limited. We discovered differentialsusceptibility of these parasitoids tospinosad, thiamethoxam, and oxamyl. The orderof toxicity for A. iole wasspinosad>thiamethoxam>oxamyl, and for T. pretiosum wasthiamethoxam>spinosad>oxamyl. Our resultsunderscored the danger of generalizingpesticide effects across even closely relatedinsects, and demonstrated that novel`selective' insecticides are highly toxic toA. iole and T. pretiosum.