Nontarget Effects of Host-Specific Biocontrols: Direct and Indirect Effects of Biocontrols that Subsidize Native Consumers

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The indirect effects of consumers in food webs are known to be important in ecological systems, but this knowledge has not been well integrated into applied fields such as weed control by biological agents. The introduction of exotic insects as biological control agents is an increasingly common strategy employed for the control of invasive plants and is thought to be ecologically safe so long as the control agents are host-specific. However, even host-specific agents may be consumed by native species and so impact the rest of the food web. This research will examine the indirect effects of an exotic gall fly, introduced to control an invasive grass species, on populations of deer mice that are key predators of insects and seeds in many western North American grasslands, and are the primary vectors for the Sin Nombre hantavirus, which causes the deadly hantavirus pulmonary syndrome in humans. Research goals are to conduct a perturbation experiment by removing gall flies from grassland plots in order to quantify the direct effect of gall fly subsidies on deer mouse populations, and measure indirect effects, which include the prevalence of the hantavirus, seed predation, germination and recruitment of native plants, and abundance of native insects. This research will advance the field of biological control by providing a means of more effectively filtering potentially hazardous insects from biocontrol programs. Additionally, hantavirus information will be disseminated to regional health authorities to help develop management guidelines to reduce human health risks associated with gall fly-mediated increases in the prevalence of hantavirus.