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Invasive Species and Biological Control: the Role of Facultative Inherited Bacterial Symbionts
Department of Entomology
In recent years, increased global commerce and travel have also increased the frequency at which organisms become introduced and established in new habitats, sometimes with devastating consequences. Invasive insects such as the emerald ash borer and the European corn borer cost billions of dollars annually, and threaten the security of our food supply when they attack crop species.
One method for controlling such invasive insects is biological control, which uses natural enemies of the pest (predators, parasitoids and pathogens) to reduce pest numbers. Biological control is an attractive alternative to pesticides because, once established, natural enemies are self-sustaining and do not require the monetary and environmental costs associated with repeated chemical applications. However, a substantial proportion of biological control releases are unsuccessful, increasing both the cost associated with biological control and the potential for unintended ecological effects.
To maximize benefit while reducing risk, we need to know as much as possible about the biology of both pest and natural enemy, to determine which natural enemies will be most capable of pest suppression. One aspect of insect biology that is just being clarified is the role of bacterial endosymbionts. Advances in molecular techniques have allowed greater investigation of these mysterious bacteria that are found within many insects, and it has become clear that they can affect many aspects of insect biology, including reproduction, dispersal, host choice, and susceptibility to natural enemies; these factors, in turn, likely influence the establishment and spread of introduced species and the effectiveness of biological control.
In this project I will investigate how symbionts might affect biological control.
First, I will use molecular techniques to identify bacterial symbionts within a series of introduced species collected from native versus exotic populations. Broad patterns of symbiont loss versus retention across species would suggest that symbionts routinely influence and/or are influenced by the process of introduction. Thus, symbionts may represent a new avenue for exploring the causes and consequences of invasiveness.
Second, I will investigate whether symbionts influence the effectiveness of a specific introduced biological control agent, the parasitoid wasp Encarsia inaron. This parasitoid is naturally infected with two bacterial endosymbionts, but can be cured of one or both symbionts. I will compare the effectiveness of parasitoids infected with different combinations of symbionts to determine whether symbionts improve or harm the parasitoid?s ability to control populations of the pest.
This model system provides a greater understanding of symbionts in introduced species, and may ultimately lead to improved biological control, either through selection of target pest species that are most vulnerable to introduced natural enemies, or through selection of biological control agents with the greatest chance for success.
2009 Project Description
The research from this project will ultimately provide information about the role of bacterial symbionts within introduced species - both invasive pests, and the biological control agents introduced to control them. At this initial stage, we have presented some of our early findings at the national meeting of the Entomological Society of America: Brady, C. M. and J. A. White. Everyone's a loser: late instar parasitism of whitefly hosts by Encarsia inaron has negative consequences for both parasitoid and host. Entomological Society of America, Dec 12-16, 2009. Runner-up, President's Prize. Wulff, J. A. and J. A. White. Do facultative symbionts influence the outcome of superparasitism in a solitary endoparasitoid Entomological Society of America, Dec 12-16, 2009.
We have started to gain information that will change knowledge about symbionts in introduced species. We have accumulated preserved specimens from multiple populations of introduced species from both their native and introduced ranges, and have begun screening these populations to determine their symbiont composition. We have also tested the larval competitive ability of a parasitoid wasp (Encarsia inaron) infected with different symbionts - our preliminary results have not shown differences between the symbionts, but many additional tests are needed before this conclusion can be drawn with confidence.
Brady, C. M. and J. A. White. Everyone's a loser: late instar parasitism of whitefly hosts by Encarsia inaron has negative consequences for both parasitoid and host. Entomological Society of America, Dec 12-16, 2009. Runner-up, President's Prize.
Wulff, J. A. and J. A. White. Do facultative symbionts influence the outcome of superparasitism in a solitary endoparasitoid Entomological Society of America, Dec 12-16, 2009.