S1058: Biological Control of Arthropod Pests and Weeds

(Multistate Research Project)

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Issues:

In the Southern Region of the US, arthropod pests and weeds (native and exotic) continue to negatively influence both agricultural and natural systems, and the growing emphasis on environmental and food safety issues has intensified interest in the development of cost-effective biological control approaches as a fundamental component of pest management. Biological control is classically defined as the "the action of parasites, predators, and pathogens in maintaining another organism's density at a lower level than would occur in the absence of the natural enemies" (DeBach 1964), and incorporates both natural biological (control is that brought about by indigenous natural enemies in the native range of a pest species) and applied biological control (importation, augmentation, and conservation). USDA-NIFA (2012) broadens the definition: the deliberate use of natural enemies - predators, parasites, pathogens, and competitors to suppress and maintain populations of a target pest species (insects, mites, weeds, plant pathogens, and other pest organisms). Despite differences in agreed upon definitions, the effective utilization of natural enemies in biological control programs is contingent upon understanding their ecology and that of their targets, their interaction with production practices, and the most effective means of using them.


Invasive pests continue to pose significant ecological and economic threats to natural and managed systems in the US and justify continued efforts in importation biological control (Frank and Fish 2008, Cuda 2009, Harwood and Parajulee 2010, Frank et al. 2011, Center for Invasive Species Management 2012). At the same time, target and non-target effects of these natural enemy introductions must be documented to assure the continued value and safety of importation biological control (McCoy and Frank 2010). Resident populations of natural enemies provide varying levels of pest suppression and therefore require continued long-term evaluation as ecological systems change following addition of exotic natural enemies (Mizell 2007). Ultimately, co-existence and effectiveness of resident and exotic natural enemies may require planned releases, but success of this approach is dependent on effective production, distribution, and release technologies for natural enemies (Van Driesche and Bellows 1996, Cuda et al. 2008).


Development and implementation of biological control programs are dependent upon effective communication and coordination of regionally-linked programs. Our multi-state research project is planned to enhance biological control of arthropod pests and weeds in the Southern Region of the US through collaboration among practitioners. This multi-state project (SDC351) provides a framework for pest target selection and coordinated research that focuses on pest / natural enemy complexes in the Southern Region.


Justification:

The mild climate of the southern US supports a great diversity of pest arthropods and plants. This moderate climate coupled with extensive international exchange in the Region creates ideal circumstances for the incursion and persistence of injurious invasive species. The need for environmentally and economically sustainable production systems is growing as social pressure for safe food and fiber increases. Research priorities have been established by the Southern Association of Agricultural Experiment Station Directors (SAAESD 2012) and include: Development of more environmentally friendly profitable production systems that utilize sustainable weed and insect management strategies that protect the environment. Furthermore, development and utilization of biologically-based tactics are emphasized as the basis for comprehensive integrated pest management systems. This increased emphasis on biologically-based management tactics includes a major re-emphasis on biological control particularly for invasive species (USDA-NIFA 2012, USDA-APHIS 2013, USDA-Forest Service 2013).


Despite dramatic changes in pesticide technologies and widespread use of genetically modified resistant crops, pest pressure remains high and insecticide use has occasionally increased in rapidly changing agricultural systems (Lundgren et al. 2009, Giles et al. 2008, Giles and Walker 2009, Harwood and Parajulee 2010). More target specific and costly pesticides are being deployed and will likely add economic burdens to growers as combinations of pesticides will be needed to achieve results comparable to those formerly attained with conventional broad-spectrum materials. Clearly, the need for developing biological control programs for pests in a wide variety of situations is more acute than ever.


Invasive species can be exceptionally destructive in the Southern Region. Many high profile invasions have occurred with severe economic and ecological effects and the threat of new invasions in this region is persistent (Harwood and Parajulee 2010, Frank et al. 2011, Onken and Reardon 2011, Ted et al. 2012). Included in the lengthy list are accomplishments reported by scientists in the previous regional research project (S-1034): the red imported fire ant, Solenopsis invicta; the B and Q biotypes of the sweet potato whitefly, Bemisia tabaci; tropical soda apple, Solanum viarum; hydrilla, Hydrilla verticillata; and the Formosan termite, Coptotermes formosanus (Goolsby et al. 2008, Overholt et al. 2009, Johnson et al. 2010, Copeland et al. 2011, USDA-National Agricultural Library 2013). The red imported fire ant invades many habitats, disturbing wildlife and native ants, damaging crops, disrupting extant biological control, and inflicting physical harm to humans and animals. The complete ecological and environmental costs of this ants damage have yet to be fully ascertained, but it is widely acknowledged that it is substantial, with estimates in excess of US $1 billion dollars per annum. Similarly, tropical soda apple is currently found in Mississippi, Alabama, Georgia, South Carolina, Tennessee, and extensively in Florida. This spined plant is highly disruptive in grazing areas and is spreading across the southeastern US. Although its spread has been slowed by herbicide based eradication efforts, this work is dependent on the ability of individuals across the region and beyond to find and correctly identify the plants. Because tropical soda apple can also grow in uncultivated and isolated areas, there is reason to suspect that the plant is more widespread than is presently acknowledged. This situation with dispersed targets and risk of being undetected, is well suited to the use of biological control agents that have the capacity to locate plants independent of human intervention.


Invasive native pests also cause extensive damage in crops and other habitats. Management of these pests by natural enemies can provide benefits ranging well beyond the locations of immediate human concern, as well as providing more proximate assistance for pest managers. This can be particularly important for highly mobile and polyphagous species such as the tarnished plant bug, Lygus lineolaris, or the beet armyworm, Spodoptera exigua. Further chemical treatment of infestations of natural areas by pests may not be economically or environmentally feasible. In these circumstances, biological control may be the only possible means of control. The advent of new technology, most notably transgenic insect resistant crops and increasingly selective herbicides, has created numerous opportunities to more adequately integrate biological control into crop production systems, particularly in the southern region (Lundgren et al. 2009, Obrycki et al. 2009, Harwood and Parajulee 2010). It has also enhanced the need for biological control, as new pests have emerged. For example, although the widespread use of Bt-transgenic cotton varieties has contributed to reduced insecticide inputs, it has also increased the problems with heteropteran pests (e.g., stink bugs, plant bugs, leaf-footed bugs) in the Southern US as insecticide spraying for lepidopteran pests has declined (Ruberson and Wickings 2008, Giles and Walker 2009). Thus, cotton producers are by necessity increasing their spray regimens to handle this new and difficult suite of pests. In addition, currently available selective insecticides are more costly and growers cannot always afford to target each individual or closely related species when the pest complex is diverse. Finally, transgenic crops may impact non-target natural enemies by directly reducing their fitness or through resource depletion (target or alternate pest decline), thus altering existing, successful natural enemy function. Development of biological control in low or targeted spray environments would be an invaluable component of IPM in these systems and would strengthen the sustainability and adoption of environmentally sound tools.


Evaluation of non-target effects is an essential element in the safe and effective implementation of any pest management tactic. Accordingly, as biological programs are developed, this project will evaluate the effects of established natural enemies on non-target organisms. These efforts will enable the development of a significant database to support meaningful risk assessment protocols for future biological control programs. For this project, it is anticipated that natural enemies will be discovered, targeted and evaluated for control of melaleuca, Brazilian peppertree, kudzu, tropical soda apple, water hyacinth, Chinese tallow, Chinese privet, knapweed, hydrilla, whiteflies, stink bugs, hygrophila, red palm mite, Hemlock wooly adelgid, tarnished plant bug, brown citrus aphid, bromeliad weevil, red imported fire ant, muscoid flies, mole crickets, and weevils. Understanding the interactions between pest management technology, conventional and novel, and natural enemies will lead to a more effective integration of biological control in pest management systems. Assessing lethal and sublethal effects of pesticides at the individual and population levels will permit effective integrated use of pesticides and biological control. In addition, quantifying the effect and interactions of indigenous natural enemies will permit the development of biologically based IPM programs for more sustainable crop/animal systems.
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