Effects of neem-based and chemical insecticides on some arthropods in alfalfa.

In this study, we tested the effects of two different doses of neem (azadirachtin) on the alfalfa weevil, Hypera variabilis Hbst. (Coleoptera: Curculionidae), aphids and predators (Coccinellids, anthocorids, chrysopids and spiders) and compared the effects with those of a broad spectrum insecticide (malathion) in a controlled experiment in 1998 and 1999. Malathion treatments reduced alfalfa weevil densities significantly (p < 0.01) by 77.9 and 87.4% in 1998 and 1999, respectively. Alfalfa weevil numbers in the low dose neem-treated plots were lower by 45.2% in 1998 and 50.2% in 1999. There were 45.3% fewer alfalfa weevils in the high dose neem-treated plots in 1999. In 1998, aphid numbers were reduced by 11.1, 25.3 and 41% in the low dose neem-treated plots, the malathion-treated plots and the high dose neem-treated plots, respectively. Aphids were more abundant in the malathion-treated plots, whereas they were fewer in the neem-treated plots compared to the control in 1999. The treatments did not have any significant effects on the total numbers of predators.