Abstract:  In this study, the acute toxicity of four fungicides, i.e., triadimefon, trifloxystrobin, prochloraz and phenazino-1-carboxylic acid, to newly emerged adults of Trichogramma ostriniae and their effects on PO activity in these wasps were determined. The results showed that triadimefon had the highest toxicity to this wasp with the LC₅₀ value of 3.27 mg/L, followed by prochloraz, trifloxystrobin and phenazino-1-carboxylic acid with the LC₅₀ values of 6.46, 4.06 and 9.72 mg/L, respectively, and their safety factors are 0.07, 0.10, 0.20 and 1.47, respectively. Phenazino-1-carboxylic acid is so evaluated as with moderate risk, while others are as with high risk to this wasp. PO activities were measured in adults that were previously treated with the four fungicides (in vivo test) and in the crude extracts that were obtained from the untreated adults and treated in vitro with the fungicides (in vitro test), respectively. At sublethal concentrations, these fungicides induced remarkably higher PO activities in vivo than in vitro, showing the obvious dosage effect. At the tested concentrations, triadimefon displayed a much more evident dosage-effect on PO activity than the other three fungicides. The results provide a basis for further exploring PO-based immune mechanisms in parasitoid wasps exposed to fungicides.

Key words: Trichogramma ostriniae, fungicide, toxicity, phenoloxidase, enzyme activity