Pesticide Research Journal Vol. 30(2): 163-167, December 2018 doi: 10.5958/2249-524X.2018.00027.4 Relative Bioefficacy of Some Newer Insecticides against Cowpea Aphid, Aphis craccivora (Koch) (Homoptera: Aphididae) SB Manjarika*, AALH Baruah, A Devee and SS Ahmed Department of Entomology, Assam Agricultural University, Jorhat 785013, Assam, India 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 LC 50 (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. Key words: Insecticides, bio-assay, relative toxicity, cowpea aphid Pulses are an integral part of human diet across the globe with potential to improve human health, conserve soil, protect the environment and contribute to global food security.India is the largest producer (25% of global production), consumer (27% of world consumption) and importer (14%) of pulses in the world. Among them, cowpea (Vigna ungiculata (L.) Walp.) is a nutritionally important legume crop commercially cultivated in India. It is also used as fodder, vegetable and green manure crop. In India, cowpea is attacked by nearly 21 insect pests right from the seedling to podding stage, out of which a handful of major importance are: aphid, Aphis craccivora Koch; jassid, Empoasca fabae (Harris); thrips, Megaleuro thrips distalis Karny; armyworm, Mythimna separate (Walker); semilooper, Thysanoplusia orichalcea (Fab.); leafminer, Phytomyza horticola Meigen and pod borer, Helicoverpa armigera (Hübner) affecting 90 per cent of plants. Out of them,aphid ( A.craccivora ) has been recognised as one of the major and economic pests of cowpea (El-Ghareeb et al., 2002) which is solely responsible to cause 20-40 per cent yield loss (Reddy et al.,2014). They cause direct damage by sucking sap from leaves, petioles, tender stems, inflorescence and pods which results in stunting, crinkling and curling of leaves, delayed flowering, shriveling of pods and ultimately reduction in yield and indirectly by transmission of mosaic virus (Rosette) and phytotoxicity as a result of saliva toxins (Atiri et al., 1986). They also secrete honey dew which retards photosynthesis, thereby leading to development of black sooty mold and leaf shedding (Kotadia and Bhalani, 1992) due to growth of saprophytic fungi covering the leaf surface and accelerating the ageing of leaves (Schepers, 1988). Earlier insecticides belonging to organochlorine (Bakhetia and Sekhon,1989),organophosphate (Mathur et al., 1987), synthetic pyrethroids (Prasad et al., 1983) and *Corresponding author E-mail: shabrin23@gmail.com