Duration of the toxicity of abamectin and spinosad on the parasitic wasp Encarsia formosa Gahan in Northern and Southern Europe.

The duration of the toxicity of two biopesticides, abamectin and spinosad, on the wasp Ellcarsia formosa Gahan, was studied at tlu'ee geographical locations: Belgium (Ghent, SooN), Spain (Madrid, 400 N), Southern Italy (Naples, 400 N), in the spring (March/April) and in the summer (June/July) of 2003, with a "worst case" laboratory test for studying the residual toxicity on adult wasps. In the spring test, for both products, statistically significant differences were found between Belgium and Southern Italy. In Belgium, abamectin was still toxic (persistence class C) after 30 days, whereas in Italy the compound was not toxic anymore after this period. Spinosad was still highly toxic in Spain (persistence class D) and Belgium (persistence class C), 30 days after treatment, while it was no longer toxic in Italy. Light intensity measurements with a StowAway logger (broad light spectrum: UV, visibl~ light, infrared) demonstrated much higher maximum daily light intensities (Lumen! m2 ) in Southern Italy than in Spain and in Belgium. In the summer test, abamectin turned out to be of very short persistence in Italy (persistence class A). In Belgium and Spain, abamectin still had to be categorised in persistence class C, five days after treatment; 14 days after treatment, no toxicity was found anymore at both locations. Five days after treatment, spinosad was toxic at all locations (persistence class D). h1 Southern Italy, the product was no more toxic, 15 days after treatment, but in Spain it was still highly toxic (persistence class D). Maximum daily light intensities during the summer experimental period were much higher in Naples than in Madrid (where three sides of the greenhouse had been covered by black gauze because of the high temperatures) and Ghent. It appears that the shorter persistence of abamectin and spinosad in Southern Italy maybe attributed to the higher light intensities in that region, both in the spring and in the summer period. The results indicate that the evaluation of the toxicity of compounds, which are sel1sitive to photodegradation, should be done with great care.