Population dynamics of aphid, Aphis craccivora Koch on cowpea ecosystem in middle Gujarat

Aphid population appeared during first week of March in summer, 2017 when crop at vegetative growth stage. Initially, its population was low, gradually increased in its numbers and attained peak level (27.14/3 cm twig) at flowering to pod developing stage during first week of April. Then after, aphid population decreased and disappeared with the maturity of crop from first week of May. Aphid incidence was found higher during 1st to 4th week of April. In kharif, 2017 population of aphid first appeared during 4th week of August and gradually increased up to the 3rd week of October and then after disappeared from 1st week of November. Its peak level (30.10/3 cm twig) was found in 1st week of October, coincide with the flowering to pod developing stage of the crop. No significant impact of studied abiotic factors was observed on aphid population. The presence of natural enemies viz., coccinellids and syrphid fly also observed in cowpea. Coccinellid was found more active than syrphid fly during both the seasons. Looking to the association among aphid and natural enemies, aphid population was found significantly correlated with the population of natural enemies i.e., coccinellids and syrphid fly, the population of aphid increased, the activity of natural enemies also increased. The population of natural enemies found highest during the peak period of aphid population in the 1st week of April and 1st week of October during summer and kharif, 2017, respectively.