Retention of mosquito larvicidal activity of lyophilized cells and WDP formulation of Bacillus thuringiensis var. israelensis on long-term storage.

Lyophilized cells (sealed and unsealed) and water dispersible powders (WDPs) of two indigenous isolates of Bacillus thuringiensis var.israelensis were stored at -10, 4, 30 and 40 degrees C for up to 4 years and checked for activity. Lyophilized cells stored in sealed condition at -10, 4 and 30 degrees C and WDPs stored at -10 and 4 degrees C were found to maintain the activity fairly well. The lyophilized cells stored at 30 degrees C and WDPs stored at 4 degrees C maintained their larvicidal property for up to 20 years. Hence, lyophilization and WDP formulations are reliable methods for long-term storage of B. t. var. israelensis.