Analytical techniques for quantifying direct, residual and oral exposure of an insect parasitoid to an organophosphate insecticide.

Abstract

Attempts at ranking the level of risk posed by pesticides to non-target invertebrates in arable crops based on their presence or absence at the time of spray application, their position in the crop canopy, and their diurnal activity patterns have been made (Jepson 1989). However, such rankings are limited by the lack of quantification of important factors that mediate short-term effects, including the susceptibility and exposure of individual species (Jepson 1988). The three main routes of pesticide exposure for a non-target beneficial species, such as adult aphid parasitoids, are uptake after direct exposure to spray droplets, uptake of residues by contact with contaminated surfaces, e.g. soil or vegetation, and oral uptake from contaminated food sources, e.g. aphid honeydew. These routes of exposure are not necessarily of equal importance, but each pose different threats to parasitoid survival through time. Therefore to extrapolate from laboratory studies to field conditions, quantitative information is needed on the relative importance of these different routes of uptake.
The determination of these exposure routes to non-target invertebrates has been applied successfully to relatively large species such as carabids and coccinellids (Wiles and Jepson 1993) and linyphiids (Jagers op Akkerhuis and Hamers 1992). However, until now it has proven impractical to use aphid parasitoids due to their small size and periodic flight behaviour. This paper reports on laboratory bioassays designed to quantify the direct, residual and oral exposures of the aphid parasitoid Aphidius ervi Haliday to an organophosphate insecticide, using two different analytical techniques.