Insecticidal Action of Rubia cordifolia L.against Plutella xylostella

Contacting,antifeeding and inhibition of growth and development of Rubia cordifolia L.on 3th instar larvae of Plutella xylostella were determined.The results showed that ethanol extract possessed high contacting and antifeeding effects against 3th instar larvae of Plutella xylostella.The LC50 of contacting action was 4.869 g/L by dipping method and the AFC50 of complete antifeeding activity were 5.965 and 6.011 g/L in 24 and 48 h,respectively.Ethanol extracts also displayed strong inhibition of growth and development on Plutella xylostella.Comparing with the controlled,the treated larvae showed big reduction on body weight,pupation rate,adult emerging rate and relative growth rate.The higher the concentration of the extracts was,the more severe the effect on the pest was.When treated with concentration of 50.00 g/L,growth inhibition rate was 98.96%,with pupation rate and adult emerging rate were 42.51% and 12.50%.