Toxic,antifeedant and growth inhibitory effects of Chenopodium ambrosioides essential oil against Pieris rapae larvae

Bioassays were employed to investigate contact toxicity,fumigant toxicity,anti-feeding and growth inhibitory functions of essential oil extracted from Chenopodium ambrosioides on Pieris rapae larvae.Dropping bioassay showed that the order of contact toxicity of C.ambrosioides essential oil to P.rapae larvae was 3rd instar2nd instar1st instar4th instar and 5th instar.There was a higher fumigant activity of the essential oil to the 3rd instar larvae of P.rapae than 1st instar,and to the 4th insatr than the 1st and 2nd instar.However,no significant differences between the 1st and the 2nd,the 2nd and the 3rd,or the 3rd and the 4th instar larvae were found.The anti-feeding assay showed that increasing concentration of essential oil decreased the anti-feeding rate,and the AFC50 (i.e.,effective concentration causing 50% antifeeding rate) of 48h was significantly higher than that of 24h.The results from the developmental inhibition assay indicated that the pupae weight and pupation rates decreased with the increasing essential oil concentration.The EC50 (i.e.,effective concentration causing 50% inhibition of pupae weight or pupation rates as compared to the control) on the pupae weight and pupation rates of P.rapae were 200.6466 μg·g-1 and 126.4382 μg·g-1,respectively.