Agricultural Research Service scientists are moving closer to developing an environmentally friendly bacteria-based biocontrol agent that offers long-lasting protection against caterpillars and other pests in a garden or cultivated field.
Bacillus thuringiensis (Bt) is now used to control gypsy moths, tent caterpillars, leaf rollers, canker worms, and other pests that attack garden plants, corn, and other crops. But the commonly used strain, B. thuringiensis kurstaki, doesn’t survive more than one generation.After an initial round of pests is killed, the biocontrol dies out and the pests return.
Michael Blackburn, an entomologist at the Invasive Insect Biocontrol and Behavior Laboratory in Beltsville, has been searching among the 3,500 characterized Bt strains in the ARS Beltsville Bacterial Collection for a strain that will not only kill an initial generation of pests, but will also survive to kill later generations.
Blackburn and his colleagues are classifying strains in the collection based on the compounds the bacteria metabolize and produce. As part of that effort, they tested 50 strains of Bt known to be toxic to gypsy moths, including kurstaki, and found they could be divided into two groups: those that produce an enzyme called “urease” and those that don’t. They fed the 50 strains to gypsy moth larvae, and when those caterpillars died, they ground them up and applied them to pellets of artificial diet. They then fed the pellets to another cycle of caterpillars.
The researchers looked at survival rates of the bacteria over several generations of caterpillars and found that urease-producing phenotypes survived better when repeatedly fed to gypsy moths. Of 26 urease-producing Bt strains, 23 survived 5 passages through gypsy moth larvae, while none of the 24 strains that don’t produce urease survived them.
The results, published in Biological Control, bring scientists a step closer to finding a Bt strain that will be more effective at combating gypsy moths and possibly other insect pests. The efforts should also lead to the discovery of Bt strains with other desirable traits, such as the ability to grow on mulch, multiply on specific crops, or thrive in gardens and other sites favored by a targeted pest.—By Dennis O'Brien, Agricultural Research Service Information Staff.
Michael Blackburn is with the USDA-ARS Invasive Insect Biocontrol and Behavior Laboratory, 10300 Baltimore Ave., Bldg. 011A, Room 281, Beltsville, MD 20705-2350; (301) 504-9396.
"Getting Closer to Better Biocontrol for Garden Pests" was published in the March 2011 issue of Agricultural Research magazine.