Many pests are exotic and have no natural enemies in Texas. Reuniting pests with their natural enemies often provides the most dramatic and sustainable method of suppressing them. The importation of such natural enemies is classic biological control. The parasite Neodusmetia successfully suppressed Rhodesgrass mealybug in Texas after being widely distributed by airplane. The search for exotic beneficial organisms which can control major plant pests in Texas is a major mission of the biological control scientists within the Department of Entomology at Texas A&M University.
Pesticides kill beneficial predators, parasites and pathogens as well as pests, and can cause outbreaks of secondary pests or rapid resurgence of pests that were initially suppressed. Using non-chemical control methods, or pesticides which kill only the target pest, protects natural enemies. Some easily seen predators are spiders, lacewings, lady beetles, ground beetles, rove beetles, syrphid flies, flower flies, hover flies, true bugs (including minute pirate bugs, big-eyed bugs and damsel bugs), predatory mites and even fire ants. However, many important natural enemies are rarely seen, such as parasitic wasps and flies (more than 8,500 species), nematodes and pathogenic bacteria and fungi.
The release of natural enemies (predators, parasites and pathogens) to control pests is a type of biological control called augmentation. This approach uses commercially available species that are applied in a timely manner to prevent population increases, or to suppress a pest population.
Natural enemies can be released all at once or over time to suppress pests or keep their numbers low. Also, the environment can be enhanced to favor natural enemies. Although research has shown that releases of natural enemies can be very effective in greenhouses and interiorscapes, outdoor releases are affected by unpredictable environmental conditions. Furthermore, if a second pest is unaffected by the released organism, pesticides used to control the second pest often eliminate the natural enemy of the first pest. Specific recommendations for Texas are still being developed.
The application of microorganisms in a manner similar to conventional pesticides is a type of augmentation. These products are referred to as “microbial insecticides.” Several products available contain varieties of the bacterium, Bacillus thuringiensis, which controls certain caterpillars, beetles and flies but does not affect other arthropods. Microbial insecticides are relatively slow acting and are most effective if applied when pest numbers are low and pests are in early stages of development.
Examples of augmentive biological control products
Commercial products available for use in augmentive biological control include microbial insecticides containing living pathogens (bacteria, fungi and viruses) and multicellular animals (predators, parasites and nematodes). Other products occasionally used with biological control agents include synthetic honeydew, flowers to attract and conserve beneficial insects in and around pest-prone or pest-infested sites, and traps using colors or scents as attractants.
Best use for augmentive products
- Purchasing and releasing natural enemies for pest suppression is a rapidly developing technology but there is still much to be learned to assure effective use of these products. Results are often difficult to evaluate and can be inconsistent because of differing conditions (e.g., environmental, meteorological, etc.). Natural enemies are living and their behavior under different environmental conditions can influence the degree of pest control. Cost-effective use of augmentive releases requires an understanding of the pest(s), natural enemies, economic goals and the environment. Commercial uses often demand intensive monitoring or scouting of the cropping system.
- Augmentive releases are meant to reduce populations at points in time. Releases at low pest densities are more effective than attempts to reduce high pest densities. Action levels or economic thresholds for release of natural enemies and effective release rate(s) have often not been established through scientific research.
- Timing of the release of natural enemies is critical since most require some time to affect the pest population. In addition, many natural enemies attack only certain life stages (e.g., egg or larval stage) of the pest. Multiple releases may also be necessary to maintain pest suppression.
- Biological control using parasites is generally pest-specific. When multiple pests occur (e.g. aphids, thrips, plus beetles), natural enemies are needed for each pest. In cases where natural enemies are unavailable for augmentation, use of a selected pesticide that spares other natural enemies may be necessary.
- Environmental conditions change dramatically and outdoor releases of natural enemies can be negatively affected by high winds, rain, hot or cold weather and other insects in the ecosystem (e.g., red imported fire ants). These factors are often unpredictable and result in erratic results from releases. Release of appropriate natural enemies in greenhouses and interiorscapes often provide more consistent results.
- Insecticide residues on the crop or site, or insecticide drift from adjacent areas, can remain toxic to natural enemies long after the pesticide was applied. Residues should be mitigated prior to releases.
What support can I expect from the companies selling these products?
Companies selling products and promoting their use should provide the consumer with directions on how to use their products, and support their claims of product performance. Insectaries and brokers, the companies producing and marketing parasites and predators, assure the delivery of viable natural enemies of the stated species or strain. They usually do not guarantee results from releases of these biological control agents even when used as directed. Although researchers and Extension faculty at The Texas A&M System are involved in evaluating some of these products, suggestions for their most effective use are still being developed.
Are these products regulated by any laws?
Microbial insecticides (bacteria, fungi, viruses) are regulated like pesticides by the Environmental Protection Agency (EPA) under the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA). Multicellular animals (arthropod predators, parasites, nematodes, etc.) are NOT registered or regulated by the EPA under FIFRA. Complaints regarding product performance can be reported to the Federal Trade Commission (FTC).
The user of purchase-and-release natural enemies must be aware of legal and biological limitations of augmentive biological control methods. Just restricting frequent use of broad spectrum insecticides often will allow a diverse group of naturally occurring beneficial organisms to survive, sometimes profoundly impacting pest population densities. As the cost of natural enemy products continues to decrease and delivery systems and methods are improved, the economic feasibility of using these methods in commercial pest control will undoubtedly improve.