Studies on Seasonal Incidence and Relative Safety of Pesticides against Coccinellid Beetles in Okra Ecosystem

Abstract

Field experiments were conducted to study the seasonal incidence and relative safety of pesticides to the coccinellid beetles, Coccinella septempunctata Linnaeus and Menochilus sexmaculatus (Fabricius) on okra during Kharif, 2002 and 2003. The appearance of the beetles started from the first week of August (1.8 and 1.7 beetles/plant) and reached its maximum (6.2 and 6.4 beetles/plant) in the first week of October in both the years. Weather parameters (minimum temperature and relative humidity) showed significant negative correlation (r = -0.7029 and r = -0.7207 in 2002 and r = -0.5932 and r = -0.6489 in 2003) with coccinellid population, whereas, maximum temperature had non-significant positive (r = 0.0716 and r = 0.4913) and rainfall had nonsignificant negative correlation (r = -0.2740 and r = -0.2380) with coccinellid population in both the years. Use of Bt (Dipel) 0.012% alone was found to be least toxic to the coccinellid beetles on okra followed by NPV 0.10% and azadirachtin (5ml/lit.). Monocrotophos (0.04%) proved highly toxic followed by acephate (0.0375%), whereas imidacloprid (0.006%), endosulfan (0.05%) and endosulfan+Bt (0.05+0.006%) were moderately toxic to the coccinellid predators in okra ecosystem.