Studies on Antifeedant Activity of 20 Plant Crude Extracts against Several Pest Insects

The insecticidal activity of 20 plant extracts against the 5th instar larvae of Pieris rapae were tested and the active ingredients of effective plants were separated primarily.The results showed that the extracts of Narcissus tazetta var. chinensis and Sapium sebiferum had very strong bioactivities against the 5th instar larvae of P. rapae.Antifeeding rate in 24 h reached 95.22% and 87.12% respectively, antifeeding rate in 48 h reached 89.64% and 79.85% respectively,corrected mortality in 7 d reached 72.56% and 54.62% respectively. Methanol extract of N. tazetta var. chinensis bulbs also had very strong antifeedant activity against Plutella xylostella,Dasychira locuples and Melanographia flexilineata Hempson. The active ingredient in N. tazetta var. chinensis bulbs mainly existed in the extract of ethyl acetate and at the concentration of 3.0 mg/mL,antifeeding rate in 24 h and 48 h reached 94.89% and 89.78% respectively.