Effects of thiacloprid, a new chloronicotinyl insecticide, on the egg parasitoid Trichogramma cacoeciae

Thiacloprid, a new chloronicotinyl insecticide, is targeted chiefly to control aphid pest species in orchards and vegetables. In a standard IOBC glass plate assay, residues of thiacloprid (SC 480) severely affected adult stages of the cereal aphid parasitoid Aphidius rhopalosiphi whereas pre-imaginal stages (which develop within the host) remained unaffected. As for A. rhopalosiphi, the pre-imaginal stages of the crop-relevant egg parasitoid T. cacoeciae were not adversely affected by a spray treatment with thiacloprid (SC 480). However, when treated host eggs were stored under greenhouse conditions, the emergence success of ecdysed parasitoids was significantly reduced. This is assumed to be caused by thiacloprid residues that had been deposited on the host egg cuticle during spray treatment and which were ingested by the parasitoids during emergence, when they were biting its way through the host egg cuticle. In contrast, if treated host eggs were subjected to field exposure conditions before emergence of the parasitoids, no statistically significant reduction in emergence success was recorded. Moreover, the fitness of parasitoids emerging from treated host eggs was not reduced compared to untreated parasitoids. Since pre-imaginal stages comprise a major part of a parasitoid population and were not affected in a lethal or sublethal way by thiacloprid (SC 480), we conclude that a spray treatment with thiacloprid (SC 480) in the field will not significantly interfere with the pest control function of a parasitoid fauna in the target crops.