Targets of augmentation. Augmentative biological controls have not been developed for all pestproblems. Indeed, relatively few situations are amenable to this approach. One of the mostfrequent uses of augmentation is to protect greenhouse crops, a practice that was started inEurope over 30 years ago in response to widespread occurrence of insecticide resistance ingreenhouse pests. Today, commercial natural enemies are available for controlling aphids, mites,scale insects, mealybugs, leafminers, thrips, caterpillars, and other greenhouse pests.
Another situation that uses augmentation is the control of filth flies in livestock manure. Severalparasites are commercially available; their impact is heightened when used in conjunction withappropriate manure handling practices. Augmentation, other than the use of microbial insecticides, has not been widely used in Midwestorchards and vineyards. It is heavily used in some areas of California, where cooperative,non-profit citrus protection districts have their own insectaries for natural enemy production. Inrow crops, generalist natural enemies are frequently used, such as the egg parasiteTrichogramma, green lacewings, and microbial insecticides. In the United States, augmentationhas probably been used the least on field crops, partly because of the lack of a complex ofeffective natural enemies, and partly because the expenses may not be acceptable on low-valuecrops.Bacillus thuringiensis is commonly used for controlling , andconsiderable research is aimed at making the releases ofTrichogramma, also for corn borer, aviable option. Home gardeners are increasingly using natural enemies to protect food crops andlandscape plants. There are several other areas where commercial natural enemies may be used,and some companies target specialized markets, such as gypsy moth, fire ant, and stored productpests. Types of natural enemies available. There are over 100 types of commercially available naturalenemies, including predatory insects and mites, parasitic insects, insect-parasitic nematodes, andinsect pathogens. Although this sounds like a high number, it is small compared to the totalnumber of pests in the United States. Further, many of these natural enemies are specialized forpests on crops such as cotton and citrus that are not grown in the upper Midwest. Othercommercial natural enemies, such as lady beetles and praying mantids, are of questionable valueeven though they have been highly popularized. Efficacy. "But do they work?" This is a frequently asked question about commercially producednatural enemies. The short answer is "Yes..., and no." The long answer requires a few hundredmore pages than the editor is willing to allocate to this article. There is no doubt thatwell-researched applications of natural enemies can be very effective. This includes the use ofmicrobial insecticides as well as many specific uses of predators and parasitic insects. There isalso no doubt that many natural enemies that are sold do not control the intended target pest(s). The reasons for the latter scenario are multiple and complex. They range from the ridiculous (myfavorite example involves a community that purchased and released lady beetles for mosquitocontrol) to the obscure. Probably the common thread that exists with "failures" is a lackknowledge. This encompasses both a lack of research needed to make recommendations forsuccessful implementation, and a lack of needed knowledge on the part of the pest managerabout the biology of the pests, the natural enemies, and their environment, all of which is crucialto making augmentation work. In this short space, my best advice for pest managers interested inembarking on a new augmentation program is to first get as much information as possible toassure a reasonable chance for success. Cost effectiveness. Some natural enemies are much easier and less expensive to produce thanothers; this is reflected in their prices. Because of the differences in prices and usage patterns, itis hard to generalize on the cost effectiveness of purchased natural enemies. Other less obviousfactors also have to be considered, especially when comparing the release of natural enemies tothe use of pesticides. These include pesticide resistance management, worker protection, impactson non-target pests, environmental considerations, and marketing practices (such as conventionalvs. organic). Another problem is that, for many commercial natural enemies and their potentialtarget pests, there is not adequate research to recommend specific release rates based upon pestpopulation levels. There are, however, many situations where augmentative biological control iscost competitive with the use of pesticides or other pest management practices. The high valueof many specialty crops reflects high production costs, including pest management. In suchcrops, the expense of biological control may be relatively low when compared to overallproduction costs. On low value crops, the use of natural enemies must be inexpensive to bejustified. This does not preclude the use of augmentation in field crops; inundative controls suchasBacillus thuringiensis andTrichogramma may be cost effective, as can be inoculative releasesthat rely on relatively low numbers of natural enemies. The cost of natural enemy releases shouldbe carefully evaluated, as with any other production cost. In summary, we in Extension get more questions about the release of purchased natural enemiesthan all other approaches to biological control. And in some cases, it is the area where we havethe fewest answers. Many augmentation programs do work and are cost effective. Butaugmentation can not be considered "the silver bullet" of biological control. It is not foolproof,and it requires a certain level of knowledge and understanding to make it work. Additionally, wehave effective commercial natural enemies for a relatively small percentage of all the types ofpests we must manage. It is the most costly and least sustainable form of biological control.However, where it does work and is cost effective, augmentation can be a very useful pestmanagement method. For further reading, refer to the bookBiological Control by Augmentation of Natural Enemies, by R. L. Ridgwayand S. B. Vinson, 1977, Plenum Press. - Dan Mahr, University of Wisconsin - MadisonReturn to Contents Menu Vol. I No. 4
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