Ecology, Environment and Conservation Paper

FLUCTUATIONS IN NATURAL REGULATION OF ACHAEA JANATA LINNAEUS LARVAE ON CASTOR BY TWO HYMENOPTERAN LARVAL PARASITOIDS, SNELLENIUS MACULIPENNIS (SZèPLIGETI) AND EUPLECTRUS WESTWOOD AS AFFECTED BY WEATHER PARAMETERS AND HOST DENSITY

G. Anitha, J. Vijay and S.J. Rahman

Abstract

Effective integrated pest management strategies of Achaea janata Linneaus on castor include conservation of its key natural enemies, two Hymenopteran larval parasitoids, Snellenius maculipennis (Szèpligeti) and Euplectrus Westwood. Information about weather and host related factors affecting these parasitoids in Hyderabad region, Andhra Pradesh, India is scant and hence, a study was taken up in farmers’ fields in kharif seasons of 2010-11 and 2011-12 to determine the degree of parasitisation of larvae of A. janata by S. maculipennis and Euplectrus and study their population dynamics as affected by weather parameters and host density. Two year observations revealed that S. maculipennis recorded a maximum of 78.9% parasitisation in the last week of August, while for Euplectrus, peak parasitisation of 35.5% was attained in the last week of September. Regression studies of larval parasitisation with weather and host density revealed that evening relative humidity; rainfall and host density had an extremely significant positive influence on parasitisation by S. maculipennis, while maximum temperature had significantly negative influence. Host density was the only factor which affected larval parasitisation by Euplectrus significantly and positively. Multiple regression equations were fitted for both the parasitoids and discussed.