PERSISTENCE OF BACILLUS-THURINGIENSIS DELTA-ENDOTOXIN AND BETA-EXOTOXIN ON STORED GRAINS AND THEIR POTENCY AGAINST PLODIA-INTERPUNCTELLA AND SITOTROGA-CEREALELLA

The persistence of B. thuringiensis, delta-endotoxin and beta-exotoxin was determined. The decrease in activity was slow over a period of 15 0 days. The reduction in larval mortality of Indian meal moth, Plodia interpunctella was more obvious with the increase of storage period an d also with the decrease of the concentration of delta-endotoxin. The decay in activity, in the case of beta-exotoxin, was more obvious at l ower concentrations than at higher concentrations as the time of stora ge increased. Data showed that the potency of the delta-endotoxin decr eased 15 days after application at 27 and 35 degrees C against both te sted species, but with a lower degree in the case of Indian meal moth. On the other hand, the beta-exotoxin showed a rapid decay 15 days aft er application on both stored wheat and crushed corn against both test ed insect species.