MODE OF ACTION OF BACILLUS-THURINGIENSIS AND NUCLEAR POLYHEDROSIS-VIRUS IN THE LARVAE OF SPODOPTERA-LITTORALIS (BOISD)

An additive effect was obtained after treatment of Spodoptera litioral is (Boisd.) larvae with a combination of Bacillus thuringiensis and nu clear polyhedrosis virus (NPVs). The NPVs was the more pathogenic foll owed by B. t., cytopathologically. Simultaneous application or B. t. a nd NPVs affected the midgut cells by causing a very specific appearanc e or cell hypertrophy with some deposits of B. t. crystals on the four th day of infection as shown by scanning electron microscopy. Transmis sion electron microscopy showed that the vegetative cells and spores o r B. t. entered the midgut epithelial cells followed by the virus. It is possible that the initial destruction caused by the B. t. toxin fac ilitated penetration and entry of the virus.