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Microbial Pesticides
Beyond Pesticides Rating: Least Toxic

Certain microbes are effective in controlling insect, fungus, and weed pest problems and are virtually nontoxic. Microbial pesticides contain living microorganisms or the toxins they produce as active ingredients. Following are just a few examples.

Milky spore disease, Bacillus popilliae is a nontoxic way to control grubs. Commercial milky spore dust is made by inoculating beetle grubs with the disease and then extracting the spores, which resemble dust or powder when dry. The spores can be applied any time except when the ground is frozen or a strong wind is blowing. Grubs become infected when they feed on the thatch or roots of grass where the spores have been applied. As the infected grubs move about in the soil, then die and disintegrate, they release one or two billion spores back into the soil. This spreads the disease to succeeding generations of grubs. If the conditions are right, grub population high and feeding vigorously, and soil is at least 70 degrees F and very moist, the disease can spread through the grub population in a week or two. In general, however, the disease should not be thought of as a quick knockdown insecticide. It may take a season or two before it has a substantial impact. It can remain effective for a decade.

Bacillus thuringiensis (B.t.) is a naturally occurring soil bacterium; it is a spore-forming rod and an insect pathogen. Different strains are toxic to particular kinds of insects. There are nearly 400 registered products that have been marketed in the country, providing effective control of such major insect pests as gypsy moths, mosquitoes, blackflies, and many others. These B.t. strains are only effective against insects in their larval feeding stages, since B.t. must be ingested to be effective. Depending on how much B.t. is ingested, insect larva soon stop feeding and are dead in a few days to a few weeks. B.t. is completely biodegradable, and does not persist in the digestive systems of birds or mammals. There is no evidence that B.t. goes on to reproduce in the wild. B.t.'s short biological half-life and high specificity makes the development of field resistance much more unlikely than with chemical pesticides if used in a targeted fashion. Infections of humans have been extremely rare. Neither irritative nor sensitizing effects have been reported in workers preparing and applying commercial products. B.t. is toxic to most caterpillars.

Beneficial nematodes are microscopic soil-dwelling worms that actively search for insects like pre-adult fleas, fire ants, or termites in the yard. After invading the larvae or pupae, they release a bacterium that kills the host within 48 hours. The nematodes then feed on the pest's body, reproduce and seek out more pests. When all larvae and pupae are killed, the nematodes die off and biodegrade. Numerous pest problems can be controlled or eliminated by using biological controls that have a minimal impact on non-target species and offer long-term solutions. Nematodes are effective in controlling ants, fleas, flies, Japanese beetles and grubs, termites, worms and caterpillars, among others.

Beneficial fungus pathogens, Beauveria spp., is a fungus that is used as a pesticide for controlling many kinds of insects. Many strains of this fungus are found worldwide in the soil. They control insects by growing on them, secreting enzymes that weaken the insect's outer coat, and then getting inside the insect and continuing to grow, eventually killing the infected pest. Available EPA information indicates that use of Beauveria spp. as a pesticide is not expected to adversely affect people or the environment and tests show that the fungus is not toxic to mammals, birds or plants. There is a potential for pesticide products containing the fungus to harm bees, so the products must not be applied near beehives or where bees are actively hunting for food.

U.S. EPA. 1999. Recognition and Management of Pesticide Poisonings. EPA 735-R-98-003. Office of Prevention, Pesticides, and Toxic Substances. Washington, DC. U.S. EPA. 1999. Biopesticide Fact Sheet Beauveria bassiana strain GHA (128924).