Assessing biological control agents for area-wide control of leafy spurge with foci in Montana and South Dakota (Aphthona lacertosa, A. nigriscutis)

Aphthona spp. (flea beetles) have been employed as biological control agents to reduce the negative impacts of leafy spurge, an invasive plant of Eurasian origin; however, information on site characteristics important to flea beetle establishment and control of leafy spurge is limited. Ninety-four sample plots were established in Montana and South Dakota in 1998 and 3,000 Aphthona lacertosa and 3,000 A. nigriscutis were released at 62 sites. Beetle abundance was estimated using insects sweeps in 1999. Leafy spurge foliar cover was estimated in 1998 and 1999. Approximately 160% more A. lacertosa than A. nigriscutis were recorded at both sites. Soil texture was the most important factor in beetle establishment. Control plot leafy spurge cover decreased by 15% in MT and 36% (P ≤ 0.05) in SD for 1999. Release plot leafy spurge cover decreased by 26% and 28% for MT and SD in 1999 (P ≤ 0.05). Reduction in leafy spurge cover in 1999 was attributed to a combination of below normal precipitation, sheep grazing, and flea beetle control.