Effects of field dosages of selected insecticides to Cotesia plutellae (Kurdjumov) (Hymenoptera: Braconidae), a larval endoparasitoid of Plutella xylostella L. (Lepidoptera: Plutellidae), were investigated under laboratory conditions. Emergence of adult C. plutellae from insecticide-treated pupae was not significantly different from the control treatment. Contact toxicity to C. plutellae adults varied greatly among the insecticides in a paper residue contact bioassay. Three azadirachtin-based insecticides, Agroneem (4.8 mg a.i.liter-1), Neemix (20 mg a.i.liter-1) and Ecozin (20 mg ai.liter-1) caused 11.1, 16.7 and 5.6% adult mortality, respectively. Of four commercial Bacillus thuringiensis (Bt) insecticides examined (all at 1.2 mg a.i.liter-1), Crymax and Xentari had no effect on adult parasitoids, whereas Mattch caused 5.6% mortality, and Dipel caused 11.1% mortality. Indoxacarb (53 mg a.i.liter-1), ?-cyhalothrin (28 mg a.i.liter-1) and spinosad (53 mg a.i.liter-1) caused 100, 88.5 and 50% adult mortalities, respectively. Low adult mortality (0~5.6%) was recorded from ingestion of azadirachtin-based, Bt insecticides and indoxacarb, compared with 100% adult mortality in treatments of spinosad or ?-cyhalothrin. Compared with the water control, ingestion of azadirachtin-based insecticides significantly reduced parasitism by 50~57%, and Bt insecticides by 8~25%. However, ingestion of these insecticides did not affect longevity of male and female parasitoid adults with one exception; female longevity was significantly reduced in the indoxacarb treatment. Insecticide residues caused considerable mortality of C. plutellae adults, 39 and 44% mortality caused by 10 d old indoxacarb and ?-cyhalothrin, respectively, and 24 and 0% mortality caused by 7 and 10 d old residues of spinosad, respectively. none