The effects of four insecticides (dimethoate, pirimicarb, imidacloprid, and spinosad) applied in an ST4 Potter tower at sublethal dosages (50% of those recommended commercially for aphid control) were studied in the laboratory on adults of Aphidius ervi (Haliday), an important parasitoid of Acyrthosiphon pisum (Harris). The most selective treatment on the hymenopteran was imidacloprid, followed in decreasing order by spinosad, pirimicarb, and finally dimethoate, which quickly eliminated the parasitoid and thus its capacity to produce progeny. Three insecticide categories were distinguished in the study. The most selective treatment was imidacloprid, followed by a group of medium toxicity formed by spinosad and pirimicarb, and last by dimethoate, which was extremely toxic to A. pisum. none