Comparative toxicity of different chemical and biological insecticides against the scale insect Dactylopius opuntiae and their side effects on the predator Cryptolaemus montrouzieri

Abstract

The contact toxicity of various chemical and biological pesticides for the first and second instar nymphs and adults of the Opuntia cochineal scale insect Dactylopius opuntiae and the predator ladybird Cryptolaemus montrouzieri was determined under Morocco semi field conditions. d-limonene (60 g/l) at 100 and 150 cc/hl, mineral oil (780 g/l) at 2400 cc/hl and malathion (500 g/l) at 300 cc/hl caused the highest mortality (99–100%) among first instar nymphs of D. opuntiae 24 h after treatment. d-limonene (60 g/l) at 150 cc/hl caused greatest mortality (99%) in second instar nymphs. The highest mortality (99%) among adult female D. opuntiae was observed 120 h after treatment with d-limonene (60 g/l) at 150 cc/hl and mineral oil (780 g/l) at 2400 cc/hl. For the predator C. montrouzieri the highest mortality (92–97%) among adults 24 h after treatment was caused by malathion (500 g/l) at 100, 200 and 300 cc/hl and alpha-cypermethrin (100 g/l) at 75, 150 and 225 cc/hl. The most harmful pesticides to C. montrouzieri larvae 24 h after treatment were malathion and alpha-cypermethrin with mortality rates of 89–95%. Mortality in larvae ranged from 87 to 100% 120 h after treatment with chlorpyriphos-methyl (480 g/l) at 75, 150 and 225 cc/hl and spinosad (480 g/l) at 100, 200 and 300 cc/hl. d-limonene (60 g/l) at 50 cc/hl and mineral oil (780 g/l) at 1000 cc/hl had the least impact on C. montrouzieri adults and larvae, causing mortality of 11 and 15%, respectively, 120 h after treatment. d-limonene (60 g/l) and mineral oil (780 g/l) may therefore be viable alternatives to others high-risk chemical pesticides. These two biological insecticides are effective in controlling the Opuntia cochineal scale insect but have little adverse impact on the predator C. montrouzieri.