BIOLOGICALLY BASED TECHNIQUES TO LIMIT THE DISPERSAL OF INVASIVE PESTS
Location: Insect Behavior and Biocontrol Research Unit
Title: Recent research trends in the use of predators for biological control
Submitted to: Biological Control of Insect Pests
Publication Type: Book / Chapter
Publication Acceptance Date: October 13, 2010
Publication Date: August 15, 2011
Citation: Legaspi,J.C., Legaspi, Jr.,B.C. and Simmons, A.M. Recent research trends in the use of predators in biological control, pp. 95-122. In Rosas-Garcia, N.M. (ed.) Biological Control of Insect Pests, Studium Press, Houston, Texas. 2011. (Book Chapter)
Interpretive Summary: Scientists at the USDA-ARS, Center for Medical, Agricultural and Veterinary Entomology (Gainesville, FL), identified recent trends in the study of predators used as biological control agents. Where species share a common resource, and are competitors, the insects may feed on each other, thereby reducing control. Analysis of predator movement is essential to monitor the effectiveness of control agents. Predators can be released using a variety of methods, or they can be attracted and maintained in non-crop or refuge crops. These practices assume that predators eventually move to the target crop to control the pest. But some refuge crops provide conditions so favorable to the predators that they prefer to remain and do not control the pest in the target crop. Genetic improvement of natural enemies will be most promising if the natural enemy is potentially effective, except for one limiting factor which is controlled mostly by a single gene. The most promising trait for natural enemy improvement is therefore pesticide resistance. Progress in this area has been limited by technological difficulties, as well as the need for caution. Scientists are aware of the risks involved in releasing insects that have been modified to be resistant to insecticides. Global warming may have significant effects on predators as biological control agents. Although predictions and generalizations are difficult to make, many scientists predict that global warming will result in an increase in the frequency and intensity of pest outbreaks. Continued population increase and demand for food, coupled with increasing demands for environmentally-friendly and sustainable agriculture, ensure that the theory and application of biological control will continue to produce critically important science.
We focus on recent interesting research trends in biological control using predators by selecting four areas of current research: 1) Intraguild predation (IGP): defined as the “killing and eating of species that use similar resources and are thus potential competitors”. In biological control, the simplest case of IGP would be that of a three-species system consisting of an herbivorous pest, a parasitoid attacking the pest, and a predator feeding on both the herbivorous pest and the parasitoid. The study of IGP has important ramifications for applied biological control, such as in the area of multiple species releases. In cases where predation effects are strong, practitioners must be careful because the deployment of IG predators may result not only in increased costs, but actually in decreased control. 2) Analysis of predator movement: Natural enemies may be deployed using several methods, including release by hand, into field cages or liberated freely, using mechanical systems from either the ground or air, or using “banker” plants. Endemic natural enemies may also be promoted through “refuge crops” which provide shelter and nutritional requirements through pollen, nectar, water and other food sources. However, the proximity of natural enemies lured by volatiles or sheltered in refuge crops does not guarantee subsequent dispersal to economic crops of interest. Precise knowledge of the movements of predators, and the effects of agronomic practices such as harvest and cropping patterns are useful for optimal biological control. 3) Genetically modified insects, with emphasis on transgenic predators: Genetic improvement of natural enemies will be most promising under the following conditions: a) the natural enemy is potentially effective, except for one limiting factor; b) the limiting trait is controlled primarily by a single gene; c) the gene can be obtained through selection, mutagenesis or cloning. Therefore, pesticide resistance is an especially promising trait for natural enemy improvement. The most significant genetically modified predator is undoubtedly the western predatory mite, Metaseiulus occidentalis (Nesbitt) (Acari: Phytoseiidae). A gene delivery method called “maternal microinjection” was developed wherein genetic material was injected directly into gravid females. Scientists are rightfully proceeding with caution in the use of transgenic insects as biological control agents because some actions may be irreversible. 4) Climatic change with emphasis on global warming: Global warming is the increase in the average temperature of the earth’s surface and waters since the mid-20th century as a result of human activities, and its predicted continuing increase. Global warming can induce changes in insect phenology, and shifts in geographic distributions. Further, these may result in decoupling of inter-specific synchronies, especially in host-parasitoid systems. Although predictions and generalizations are difficult to make, many workers predict that global warming will result in an increase in the frequency and intensity of pest outbreaks. The relentless pressures of population increase and demand for food, coupled with increasing demands for environmentally-friendly and sustainable agriculture will ensure that the theory and application of biological control will continue to produce critical and exciting science.