Relative Bioefficacy of Some Newer Insecticides against Cowpea Aphid, Aphis craccivora (Koch) (Homoptera: Aphididae)

Abstract

Relative toxicity of insecticides viz., clothianidin, bifenthrin, imidacloprid, spinosad, thiacloprid, flubendiamide, flonicamid and dimethoate is reported against cowpea aphid, Aphis craccivora Koch. Clothianidin @100 g a.i ha−1 was the most effective in bringing down the population of aphid at 1, 3, 7 DAS, while at 10 DAS, dimethoate (450 g a.i. ha−1) recorded the lowest incidence of aphid population (4.49 number per plant) with highest per cent reduction (79.19). The highest mean yield of 13.08 q ha−1 was obtained from dimethoate 450 g a.i. ha−1 followed by imidacloprid 20 g a.i. ha−1 (12.25 q ha−1) as compared to the lowest in the untreated plots (9.17 q ha−1). The highest benefit was achieved in the plots treated with imidacloprid 20 g a.i. ha−1 with a benefit-cost ratio of 8.72: 1 whereas the lowest benefit cost ratio of 0.37: 1 was obtained from the plots treated with spinosad 45 g a.i. ha−1. In laboratory, following dry film bioassay, the LC50 (at 24 h) of clothianidin, bifenthrin, imidacloprid, spinosad, thiacloprid, flubendiamide, flonicamid and dimethaote were found to be 0.031, 0.117, 0.063, 0.912, 0.042, 0.027, 0.079 and 0.057 ppm with the order of toxicity flubendiamide> clothianidin > thiacloprid > dimethoate >imidacloprid >flonicamid> bifenthrin >spinosad, respectively. Taking dimethoate as unity, the order of relative toxicity of insecticides was: flubendiamide (2.11)> clothianidin (1.83)> thiacloprid (1.35) > imidacloprid (0.90)>flonicamid (0.72)> bifenthrin (0.48)>spinosad (0.06) at 24 h. It was concluded that though dimethoate 450 g ai. ha−1 was an equally effective insecticide against A. craccivora as imidacloprid, the latter was more effective in terms of aphid population reduction, yield and benefit-cost ratio. Considering the LC 50 values and relative toxicity against A. craccivora, flubendiamide 60 a.i ha−1 was the most toxic and spinosad 45 a.i ha−1 the least toxic among the tested chemicals.