EFFECT OF FLEA BEETLES (APHTHONA NIGRISCUTIS) ON PRAIRIE INVADED BY LEAFY SPURGE (EUPHORBIA ESULA) IN MANITOBA

Leafy spurge (Euphorbia esula) is an invasive exotic weed in Great Plains rangelands and pastures. Aphthona nigriscutis, the black dot flea beetle, was released as a biological control agent in nine heavily infested sites in south-central Manitoba (three sites in 1986, three in 1988, and three in 1990). In 1992 we evaluated beetle impact by sampling the vegetation in 25 × 25 cm quadrats. We measured cover, height, density, and biomass of leafy spurge, the cover of litter and bare ground, and the presence of other plant species both at the release point and at randomly-chosen nearby nonrelease reference points at each site. Leafy spurge near the release points showed significantly lower cover, biomass, height, and stem density than at the reference points. Also, release points had significantly more bare ground, higher grass and sedge biomass, and greater plant diversity. Other plant species, especially perennial grasses and sedges, increased in frequency, while frequency of leafy spurge did not change over time. Data such as these are important if we are to employ management techniques that can both reduce invasive weeds and restore native species diversity to the Great Plains prairies and rangelands.