A field study was conducted to assess the establishment of Aphthona lacertosa and A. nigriscutis (Coleoptera: Chrysomelidae) used in a biological control program for leafy spurge, Euphorbia esula L., and the level of leafy spurge control in Minnesota. Twenty-six sites where Aphthona spp. were previously released were sampled in western Minnesota in 2000, 2001 and 2002. Our results suggest that A. lacertosa is the most abundant species and likely the species that is most important in the control of leafy spurge in Minnesota. Aphthona lacertosa established at 100% of the release sites and abundance of leafy spurge was significantly reduced in all study sites. Aphthona nigriscutis established at 73% of the study sites, but at significantly lower densities than A. lacertosa. At a majority of the sites, significant reductions were achieved within two to three years after introduction of one or both species. Differing site characteristics did not prevent control of leafy spurge in Minnesota by A. lacertosa and A. nigriscutis. Aphthona lacertosa, in particular, was able to establish and populations expanded across a range of sites with differing characteristics. We suggest that introducing five to ten thousand A. lacertosa or a combination of A. lacertosa and A. nigriscutis, can be an effective management strategy. For the purpose of monitoring and collecting A. lacertosa, we recommend that release sites be visited at a minimum of two years post release. Once leafy spurge reduction occurs, A. lacertosa populations also begin to decline rapidly, limiting opportunities to collect beetles for redistribution.
Species 1: Coleoptera Chrysomelidae Aphthona lacertosa
Species 2: Coleoptera Chrysomelidae Aphthona nigriscutis
Keywords: Biological Control, Leafy Spurge
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