Biocontrol Deconstructed, Part 2

The hemlock woolly adelgid has destroyed millions of acres of Eastern hemlocks in the Eastern United States. Other invasives such as the gypsy moth, bean plataspid, and Asian longhorned beetle wreak economic and ecological havoc every year, with few available chemicals to control them. Biological control is often a viable option for pest management when other available controls are not feasible or do not work.

Exotic invasives, whether they are insects, diseases or weeds, cause about $100 billion in damage every year. In public settings such as state forests, pest management specialists use extreme caution when using pesticides. Because of visitors, trees cannot be sprayed. Some infested areas are near streambeds or other areas where rare or endangered species live, species that may be sensitive to the chemicals. Some chemical pesticides persist in the soil, making them unsuitable for use in ecologically sensitive areas. On farms, consistently using pesticides, especially where only one or two have been labeled for use on a crop, encourages pesticide resistance and can eventually become useless for controlling the pest.

Every insect has a natural enemy. One of the main differences between native pests and exotic pests is the proximity of the enemy. For a pest indigenous to the U.S., for instance, specialists search for natural enemies within the immediate area. For a population of thrips attacking a fruit farm, for instance, many specialists will recommend that the grower use pesticides sparingly to conserve the natural enemies (usually lady beetles). Pest insects seem to develop resistance to chemical pesticides long before beneficial insects do.

In Texas, extension specialist Monti Vandiver encourages his growers to scout their fields for insects, both destructive and beneficial. In one instance, he encouraged a cotton grower to delay spraying for cotton thrips because he noticed a population of ladybugs developing nearby. In a week, the ladybugs descended on the thrips and annihilated the population. The cotton field was saved without a single spray. Read the story.

The enemies of an exotic invasive are usually in the invasive’s native land, too far away to help control the pest in the U.S. In those cases, scientists will return to the insect’s native land and try to breed a population of natural enemies, studying the natural enemies under several different situations to be sure that the new insect does not become a pest in a new country.

To control the invasive fire ant, for example, scientists traveled to the ant’s homeland of South America to find the phorid fly. In South America, fire ant populations are only 20 percent of what they are in the U.S. Auburn University has been at the forefront of finding predators and fungal diseases to control fire ants and has released phorid flies in several counties, with success. These biocontrol technologies are helping to reduce fire ant populations to lower the amount of chemical applications necessary to pour on fire ant mounds.

The Cornell University site has a few additional success stories about invasive pests that are currently being managed through biological control methods.

However, as any other intervention, biological control has risks. Next week I’ll look at some of the risks of biocontrol.

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