Measurement of insecticide uptake and effective fraction in a beneficial insect using solid-phase microextraction

The determination of insecticide uptake in beneficial insects is important for quantifying the doses that are responsible for the toxicological effects and to compare them with the doses that insects may absorb in treated fields. Because of the small size of some beneficial species, the amount of insecticide absorbed may be very low. Herein, we present a method that relies on the sensitivity and specificity of SPME (solid-phase microextraction) as a sampling technique that can be used to measure very small amounts of an organophosphorus insecticide in small insects. In our study, the method was applied to quantify the internal dose and free dissolved fraction of chlorfenvinphos in beneficial parasitoids exposed through a topical application. Up to 0.5 ng of the insecticide could be quantified in these fractions, that is, 10 times less than when using solvent extraction techniques. The penetration and elimination rates of the insecticide in the insect were also determined. The method proved to be suitable to quantify internal doses in parasitoids collected in a treated field.