Biological Activities of Two Oxadiazole Derivatives against Vegetable Pest Insects

The activity of two novel 1,3,4-oxadiazoles containing a 2H-pyridazin-3-one group (HL-19) and symmetrical benzene group (HL-25) were taken into investigation on vegetable pest insects by laboratory assays and field tests. The results showed that HL-19 could strongly inhibit the growth and development of the six lepidopteran larvae such as Pieris rapae. Mythimna separata larvae were most sensitive with IC50 0.11 mmol/L. HL-19 also exhibited considerable antifeedant activity against the larvae of M. separata, P. rapae, and Plutella xylostella, which were decreased with the growth of insects and always slightly inferior to the action of azadirachtin, the non-choice antifeeding activity of HL-19 against M. separata and P. rapae larvae exceeded 65% and its choice antifeeding activity against 2nd instar larvae of M. separata was 2.43 μg/cm2 . However, HL-25 possessed slow lethal activity against the lepidopteran larvae and lost antifeedant action, the highest activity was against M. separata larvae with LC50 0.06 mmol/L. HL-19 and HL-25 could kill the apterous Aphis craccivora adult with LC50 0.13 mmol/L and 0.24 mmol/L. Furthermore, field tests of HL-19 and HL-25 against P. rapae obtained 86.4% and 74.6% control efficiency respectively.