Cross infectivity of baculovirus, Spilarctia obliqua nuclear polyhedrosis virus against mulberry pest, Porthesia xanthorrhoea Kollar.

Spilarctia obliqua nucleopolyhedrosis virus (SoNPV) has been found effective against S. obliqua (Walker) as well as Porthesia xanthorrhoea Kollar. LC50 concentration of S. obliqua SoNPV against S. obliqua and P. xanthorrhoea was 2.5 x 10(4) and 3.7 x 10(4) POBs/ml, respectively. LT50 of SoNPV against S. obliqua was 5.73 days, while it was 6.98 days for P. xanthorrhoea. Cross infectivity of SoNPV against P. xanthorrhoea and ease of its mass production may make it an ideal biopesticide.

Changes in haemolymph constituents of American bollworm, Helicoverpa armigera (Hübner), infected with nucleopolyhedrovirus.

Six types of haemocytes viz., prohaemocytes, plasmatocytes (round, fusiform, vermiform and spindle shaped), granular cells, spherule cells, oenocytoids and adipohaemocytes were found in the haemolymph of larvae of American bollworm H. armigera. The total and differential haemocyte counts (THC and DHC) in H. armigera haemolymph were affected by nucleopolyhedrovirus (NPV) treatment. There was a general decrease in THC in response to NPV treatment in both young and old larvae. However the decrease was more apparent in 5 and 8 day old larvae than in 10 day old larvae. The differential haemocytes showed less of granular cells and more of spherule cells and prohaemocytes in the old larvae. Plasmatocytes and granular cells in 10 day old larvae initially phagocytosed polyhedra; however, disintegrated after 3 to 4 hr. The haemolymph of NPV treated larvae melanized slowly particularly in old larvae. Phenoloxidase (PO) activity decreased positively with granular cells and oenocytoids in 10 day old treated larvae. Cellular fraction had high level of PO activity, which was transferred to plasma in response to NPV infection in the older larvae. The role of NPV pathogenesis vis-à-vis immunity in insect is discussed.