Bioefficacy and Persistence of Insecticides against Blister Beetle, Mylabris pustulata (Thunb.) in Pigeonpea, Cajanus cajan (L.) Millsp.

Blister beetle, Mylabris pustulata (Thunb.) is a polyphagous pest attacking flowers of pigeonpea (Cajanus cajan), cotton (Gossypium sp), lady's finger (Abelmoschus esculentus), mungbean (Vigna radiata), urdbean (Vigna mungo), ricebean (Vigna umbellata) etc. throughout the country. Because of its polyphagous feeding nature and hard protective adaptation against insecticides, long term management of this pest with a single molecule is difficult. Therefore, field cum laboratory experiments were carried out for three consecutive cropping seasons during kharif 2008–09, 2009–10 and 2010–11 to find out the persistence and efficacy of different insecticides. It was found that decamethrin 2.8EC was 3334 times toxic with lowest LC₅₀ value (0.0000563) followed by monocrotophos 36SL as compared with endosulfan which was the least toxic with LC₅₀ value (0.1877). Insecticides evaluated for their persistent toxicity during 2009–10 revealed that decamethrin and thiodicarb caused cent per cent mortality of adult blister beetle immediately after spray. At 8^th days after spraying, decamethrin caused 60 per cent mortality. Insecticides evaluated for their efficacy during the year 2010–11 revealed that the plants were found free from adult blister beetle population in treatments involving decamethrin and cypermethrin even at ten days after spray. Among all the treatments, spraying of thiodicarb 75WP @ 625 g ha⁻¹ provided the highest grain yield (18.87 q ha⁻¹). Maximum cost-benefit ratio was observed in monocrotophos 36SL, cypermethrin 25EC and decamethrin 2.8EC.