Insecticidal activity of cashew nut shell liquid against sucking pests of cowpea, Vigna unguiculata subsp. sesquipedalis (L.) Verdc.

Cashew nut shell liquid (CNSL), an important agro waste from cashew nut processing factories, was emulsified in water and assayed for insecticidal activity at concentrations ranging from 0.05 to 0.2 % against aphid, Aphis craccivora and pod bug, Riptortus pedestris infesting cowpea, Vigna unguiculata sesquipedalis under laboratory conditions by topical application. CNSL at various concentrations was found to have insecticidal properties against A. craccivora and R. pedestris wherein the speed of kill and efficacy varied with concentration and test insect. CNSL @ 0.1 % with mortality ranging from 95.83 to 100 per cent at 48 hours after treatment (HAT) was found effective against A. craccivora whereas a concentration of 0.2% was required against R. pedestris to achieve similar mortality (96.67 to 100 %) at 72 HAT. CNSL derived from two cashew nut processing methods (drum roasting and steam boiling) did not differ significantly in their insecticidal action. At concentrations of 0.1 and 0.2 %, mortality produced by CNSL was comparable to that of chemical insecticide, thiamethoxam 0.03% and significantly superior to the widely used botanical neem oil @ 2% against A. craccivora and R. pedestris respectively. R. pedestris that survived exposure to CNSL treatments exhibited developmental abnormalities and formation of nymphal adult intermediary indicating its possible insect growth regulatory effect.