Efficacy of Chinaberry tree (Meliaceae) aqueous extracts and certain insecticides against the pea leafminer (Diptera: Agromyzidae)

Abstract

Aqueous extracts of fruits and leaves of the Chinaberry tree, Melia azedarach L. were tested for their efficacy versus other biotic and synthetic insecticides against the pea leafminer, Liriomyza huidobrensis (Blanchard). The study included field experiments on naturally infested swiss chard, Beta vulgaris var. Cicla L., and greenhouse experiments on artificially infested cucumber, Cucumis sativus L. that were conducted in 1995–96. The other treatments included azadirachtin (0·25%), ultrafine mineral oil, abamectin, cyromazine, imidacloprid, pyrazophos and control. Results of field experiments indicated that Melia fruit extract and the other insecticides significantly lowered the number of larvae per swiss chard plant as compared to the control, at 5 days sampling after second spray or 15 days after first spray, when two consecutive sprays were performed. However, at 10 days after second spray, the fruit extract did not differ significantly from the control, but it was comparable in its effect to the insecticides, except abamectin and cyromazine. In greenhouse experiments, the pea leafminer larvae were found at higher densities on cucumber leaves located at the lower plant part (10–60 cm) compared to other leaf positions. The Melia fruit extract and the other pesticides significantly decreased the number of live larvae per cucumber leaf compared to the control, 10 days after each spray. The fruit extract, abamectin, cyromazine, imidacloprid and pyrazophos lowered the leafminer population significantly compared to the control, throughout the period of the experiments. However, the fruit extract was significantly less effective than these insecticides at the final count, 20 days after second spray. Abamectin and cyromazine consistently showed a significant decrease in number of larvae, in both field and greenhouse experiments. At certain periods of the experiments, Melia extracts were comparable in their efficacy to the tested commercial biorational and synthetic pesticides. Thus, they have a good potential to be used in the management of the pea leafminer. This is the first report for use of M. azedarach against L. huidobrensis.