Phyllis A.W. Martin, Robert R. Farrar Jr., Michael B. Blackburn
USDA/ARS Invasive Insect Biocontrol and Behavior Laboratory, Henry A. Wallace Beltsville Agricultural Research Center, Agricultural Research Service, United States Department of Agriculture, Bldg. 011 HH 17, BARC-West, Beltsville, MD 20705, USA.
Bacillus thuringiensis is an entomopathogenic bacterium that can kill a variety of pests, but seldom causes epizootics because it replicates poorly in insects. We have tested lepidopteran-toxic B. thuringiensis strains with diverse substrate utilization profiles for the ability to survive repeated passages through larvae of the gypsy moth, Lymantria dispar, without intervening growth on artificial media. These experiments have revealed a remarkable correlation between the production of urease by the bacteria and its ability to survive repeated passages through larvae. Of 26 urease-positive strains tested, 23 were capable of surviving five passages through gypsy moth larvae. In contrast, none of the 24 urease-negative strains tested survived to the 4th passage, with only three strains surviving to the 3rd passage. Selection of B. thuringiensis strains with phenotypic traits favoring replication in the environment, such as urease production, may improve their efficacy as biological control agents.