Development of Achaea janata granulosis virus formulation for use as a viral biopesticide in the management of semilooper on castor

Abstract

Bio-efficacy of granulovirus (GV) infecting the semilooper, Achaea janata L., a serious defoliating pest of castor bean, Ricinus communis L., was established through leaf disc bioassays. Ovoid occlusion bodies (OB) of A. janata GV (AjGV) measuring 480±20.9 by 240±13.7 nm contained a singly embedded nucleocapsid. Estimated molecular weight of viral genomic DNA obtained with three restriction enzymes was in the range of 124 and 127 kb with a mean of 125.7±0.9 kb. Estimated median lethal concentration (LC50) of AjGV mother culture to second instar larvae was 2.2±0.21×106 OB/ml or 85.4±9.7 OB/mm2 leaf, while for the formulation it was 3.1±0.89×106 OB/ml or 123.3±35.1 OB/mm2 leaf. Kaplan-Meier survival estimate of median lethal time (LT50) for second instars was 7 days at 5×108 OB/ml concentration and 12 days at 5×106 OB/ml. AjGV mother culture and formulation were found to be non-toxic in all the mandatory mammalian toxicity tests. This study fulfills the key data requirements on identification of the AjGV Hyderabad isolate, its bio-efficacy and safety in mammalian toxicity tests.