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Published online by Cambridge University Press: 19 September 2011
Persistence of four insecticides (prothiofos, Bacillus thuringiensis Berliner, fenveralate and methamidophos) were evaluated against the larvae of Plutella xylostella (L.), under field conditions. The effective biological action of the chemicals against the larvae varied with different instars. The insecticides were biologically effective for 6 to 8 days after treatment against first and second instars, and their index of persistent toxicity was higher than that for third and fourth instars. They were effective against third and fourth instars only for one day after spraying. Prothiofos and B. thuringiensis were more toxic to all the instars than methamidophos or fenveralate.
La persistence de quatre insecticides (prothiophos, Bacillus thuringiensis Berliner, fenveralate et methimidophos) a ete evaluee contre les chenilles de Plutella xylostella (L.) sous les conditions des champs. L'action biologique effective contre l'espece etait variable selon les stades larvaires. Les produits chimiques etaient active biologiquement pour une duree plus longue (six a huit jours apres le traitement) contre le premier et le deuzieme stade larvaire. Les indices de toxicite persistente de ces produits chimiques etaient plus hauts pour ces stades larvaires que pour le troizieme et le quatrieme stade larvaire. La periode de persistence etait reduite jusqu'un jour apres le traitement pour le triozieme et quatrieme stade larvaire. Prothiophos et B. thuringiensis montraient une toxicite plus grande pour tous les stades larvaires.