Abstract
Trichogramma chilonis is an important biological control agent (parasitoid) that kill the host species before they damage the crops. However, insecticide sprayed after T. chilonis release significantly alter its efficacy. The acute toxicity risks of neem seed extract and commonly used insecticides for the control of lepidopteran insects are unknown for T. chilonis. The main objective of this study was to assess the toxicity of four insecticides, i.e., buprofezin, lufenuron, methoxyfenozide, pyriproxyfin and neem seed extract to T. chilonis.
Egg card and dipped surface bioassays were used to test the toxicity insecticides, i.e., lufenuron (2 ml/liter), methoxyfenozide (2 ml/liter), buprofezin (5 g/liter), pyriproxyfin (5 ml/liter) and neem seed extract (2 ml/liter). Egg cardboards prepared from the parasitized eggs of Sitotroga cerealella collected at 1st, 3rd, 5th, 7th, and 8th day after oviposition were dipped in the respective concentrations of inleticides and neem seed extract. The dipped cardboards were dried and emergence of T. chilonis was recorded. Similarly, dipped surface bioassay was conducted to observe the mortality of T. chilonis at 4 and 24-h after exposure.
The applied insecticides exhibited varying degree of toxicity against T. chilonis. Lufenuron and neem seed extract proved least toxic, methoxyfenozide and buprofezin were moderately toxic and pyripoxyfen exhibited the highest toxicity during the study. Similarly, lufenuron and neem seed extract proved less toxic for the adults, buprofezin was moderately toxic, and methoxyfenozide and pyripoxyfen exhibited the highest toxicity in the dipped surface assay after 4 h of exposure. All insecticides proved highly toxic for the adults 24 h after exposure. The results reveled that lufenuron and neem oil are relatively safe for T. chilonis.
The tested insecticides and neem seed oil exhibited varying degree of toxicity against T. chilonis. The overall toxicity was classified as; pyriproxyfen > methoxyfenozide > buprofezin > lufenuron > neem seed extract. Therefore, neem seed extract and lufenuron are safer for T. chilonis compared to the rest of the insecticides included in the study.