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

Thiacloprid, a new chloronicotinyl insecticide, is targeted chiefly to cont rol aphid pest species in orchards and vegetables. In a standard IOBC glass plate assay, residues of thiacloprid (SC 480) severely affected adult stag es of the cereal aphid parasitoid Aphidius rhopalosiphi whereas pre-imagina l stages (which develop within the host) remained unaffected. As for A. rho palosiphi, the pre-imaginal stages of the crop-relevant egg parasitoid T. c acoeciae were not adversely affected by a spray treatment with thiacloprid (SC 480). However, when treated host eggs were stored under greenhouse cond itions, the emergence success of ecdysed parasitoids was significantly redu ced. This is assumed to be caused by thiacloprid residues that had been dep osited on the host egg cuticle during spray treatment and which were ingest ed by the parasitoids during emergence, when they were biting its way throu gh the host egg cuticle. In contrast, if treated host eggs were subjected t o field exposure conditions before emergence of the parasitoids, no statist ically significant reduction in emergence success was recorded. Moreover, t he fitness of parasitoids emerging from treated host eggs was not reduced c ompared to untreated parasitoids. Since pre-imaginal stages comprise a majo r part of a parasitoid population and were not affected in a lethal or subl ethal 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.