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6.  ECOLOGICAL BARRIERS FOR THE ESTABLISHMENT AND POPULATION INCREASE OF FLEA BEETLES ON LEAFY SPURGE

Robert Nowierski1, David Kazmer2, David Horvath3, and Richard Hansen4

Abstract: Ecological barriers were investigated that may negatively affect the establishment and population increase of the five flea beetle species released against leafy spurge. Habitat association models of the flea beetles, developed from European data, were validated with insect, plant, and soil data collected from 48 research sites in Montana, North Dakota, and Wyoming. European and U.S. habitat association models were found to be statistically similar. The genetic variability of leafy spurge is being evaluated using AFLP (Amplified Fragment Length Polymorphism) techniques. Preliminary results have shown relatively little genetic polymorphism either within or among spurge populations. The results of Flea beetle sex ratio studies showed that populations of Aphthona nigriscutis have a highly female-biased sex ratio, while those of A. cyparissiae, A. flava, and A. lacertosa are close to a 50:50 sex ratio. Greater than 85% of the A. nigriscutis populations were infected with parasitic bacterium, Wolbachia spp., which has been shown to cause female-biased sex ratios in other insect species. None of the other Aphthona species sampled was found to be infected with Wolbachia spp. The ecological amplitude of leafy spurge is being assessed using geographic, soil, and plant community information obtained from TEAM leafy spurge research sites. The impact of the flea beetles on plant species richness and diversity was evaluated at four research sites in Montana and North Dakota. By reducing high cover levels of leafy spurge the beetles may increase the diversity and species richness of forbs and may contribute to a substantial increase in the cover of grasses compared to areas still dominated by spurge.
 


1Department of Entomology, Montana State University, Bozeman, MT. Presenter; 2Department of Renewable Resources, University of Wyoming, Laramie, WY; 3USDA-ARS, Fargo, ND; 4USDA-APHIS-PPQ, Montana State University, Bozeman, MT

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