EFFECTS OF AQUEOUS NEEM LEAVES EXTRACT ON 4TH STAGE LARVAE OF PLUTELLA XYLOSTELLA (LEPIDOPTERA: PLUTELLIDAE)

Résumé

ABSTRACT

The diamond back moth, Plutella xylostella Linnaeus, 1758 (Lepidoptera: Plutellidae) is improperly and excessively controlled with synthetic insecticides in vegetable crops. Neem (Azadirachta indica A. Juss) is reported to be an alternative to those synthetic insecticides in the control of many insect pests including P. xylostella. The aims of this study are to evaluate the toxic, the antifeedant and the post- treatment effects of neem leaves extract, on the 4^th larvae of P. xylostella compared to those of synthetic insecticides (Conquest Plus 388 EC and Cydim Super). Exposure of larvae on cabbage leaves (Ø = 90 mm) treated or not during 24 h, showed mortality rates between 1.67 and 13.33% (P < 0.05). Larvae consumed between 99.50 ± 7.96 and 309.50 ± 35.57 mm² of the surface of treated cabbage leaves (p = 0). The emerging rate of P. xylostella adults was lower 57.78 ± 13.04 for neem leaves extract compared to controls and insecticide treatments whose rates were from 65.32 ± 7.34 to 89.63 ± 4.23% (p = 0). Neem extract caused wing damage to 21.86% of emerged P. xylostella, compared to the controls and insecticide treatments with no recordof wing damage (P = 0). The neem leaves extract was more effective than synthetic insecticides in the control of P. xylostella. It enhanced the management of 4^th instars larvae of P. xylostella by regulating its development to adults and deforming wings. Therefore it can be considered as a new hope in developing a management program against P. xylostella.

Key words: Plutella xylostella, aqueous neem leaves extract, cabbage