Better Biocontrol in the Future

By Susan Littlefield

While none of us want to see our gardens decimated by insect pests, few of us want to control pests with toxic sprays that can harm us and the environment. So it's encouraging to learn of the progress researchers at the USDA's Agricultural Research Service are making in improving on the well-known microbial insecticide called B.t.

Short for Bacillus thuringiensis, this environmentally friendly bacterial pesticide is used to control caterpillars of all sorts both by home gardeners and commercial growers and farmers. But the most commonly used strain, B. t. kurstaki, only survives for one generation. After the initial pest infestation is killed, the bacteria die out, leaving no protection against future infestations.

Entomologist Michael Blackburn tested 50 strains of B.t. known to be toxic to the larvae of gypsy moths and found they could be divided into two groups based on their ability to produce an enzyme called urease. He fed all the strains to gypsy moth larvae; when the larvae died they were ground up and applied to food pellets that were then fed to a new generation of caterpillars. He discovered that the strains that produced the enzyme survived better over the course of repeated feedings than those without. Most of the urease-producing strains survived five successive passages through gypsy moth larvae.

It is hoped that this research will pave the way for the development of more effective B.t. strains, perhaps ones that will be able to grow on mulch, multiply on specific crops, and persist in gardens. The development of such long-lasting biocontrol would be a boon to gardeners and a big benefit to the environment.

For more information on this research, go to: ARS.

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