Evaluation of insecticides against cotton mealybug, Phenacoccus solenopsis Tinsley and their safety to important predators

Abstract

Cotton plays an important role in the world economy by supplying raw materials to different manufacturing units. Of late, it is being seriously attacked by the cotton mealybug, Phenacoccus solenopsis Tinsley. The biological control involving coccinellid beetles and chrysopids as predators could lead to ecologically sustainable mealybug control. Here, in the context of conservation of natural enemies, we exploredthe efficacy of insecticides on the cotton mealybug and also safety to other predators. Six insecticides viz; chlorpyrifos 20 EC (0.05%), endosulfan 35 EC (0.07%), monocrotophos 36 SL (0.04%), malathion 50 EC (0.12%), dichlorvos 76 EC (0.15%), and alphamethrin 10 EC (0.01%) were tested for their residual toxicity against the mealybug, P. solenopsis and its coccinellid predators. Studies revealed that, both chlorpyrifos and malathion showed highest toxicity in terms of mean mortality (100%) to female mealybugs at 24 h of exposure as against lowest in endosulfan (35%). Interestingly, chlorpyrifos and dichlorvos, which proved toxic to mealybug were less toxic to the grubs of Cryptolaemus montrouzieri, registering only 21.66 per cent and 34.16 per cent mortality, respectively. These insecticides when offered to the adults along with honey differed in toxicity as stomach poison at 24 hrs of exposure. Endosulfan registered mortality to the tune of 60 and 70% against Coccinella septempunctata and Cheilomenes sexmaculata, respectively. However, stomach toxicity pertaining to the insecticide-sprayed mealybugs as prey offered to all the three species of predators indicated that the insecticides, chlorpyrifos and endosulfan were lesser toxic to these wherein mean mortality ranged from 38.09 to 56.66 and 50 to 65.71%, respectively. Dichlorvos was the most toxic, registering 100% mortality for all 3 predators viz. Nephus regularis, Scymnus coccivora and Hyperaspis maindroni. The release of C. montrouzieri coupled with chlorpyrifos is likely to be a better option for the management of mealybugs infesting several agri-horticultural crops.