Eco-Toxicological Effect of Insecticides on the Larval Parasitoid, Bracon brevicornis Wesmael (Hymenoptera: Braconidae)

Laboratory tests using the dry film method were conducted to assess the toxicity of different commonly used insecticides and insect growth regulators to Bracon brevicornis. The carbamate insecticide, carbosulfan, was highly toxic to B. brevicornis with a LC50 value of 0.0001 mg a.i./l, whereas pymetrozine and buprofezin had LC50 values of 0.1056 and 0.0374 mg a.i./l, respectively. Among the three neonicotinoids, acetamiprid showed the highest toxicity to B. brevicornis with a LC50 of 0.0041mga.i./l followed by thiamethoxam and imidacloprid. The order of toxicity based on the LC50 values was: carbosulfan > lambdacyhalothrin > bifenthrin > indoxacarb > acetamiprid > thiamethoxam > imidacloprid > buprofezin>pymetrozine. Pymetrozine showed slight to moderate toxicity to B. brevicornis, with a risk quotient (RQ) of 1420, while the RQ value for all other insecticides were dangerously toxic to B. brevicornis. The mean activity of cytochrome P450 in B. brevicornis was 4.2817 nM/mg protein with a frequency distribution ranged from 3.001 to 5.446 nM/mg protein. The mean activity of acetyl choline esterase in B. brevicornis was 1.7056 nM/Min with a frequency destitution ranged from 0.7572 to 3.1951 nM/Min. The mean activity of carboxylesterase was 37.5 mOD/Bracon/min with a frequency destitution ranged from 27.8 to 47.1 mOD/Bracon/min. Use of selective insecticides to conserve B. brevicornis may improve the compatibility of biological control with the IPM programme.