Impacts of Galerucella calmariensis and G. pusilla on Lythrum salicaria In Indiana

Abstract

Lythrum salicaria, an invasive wetland hydrophyte native to Eurasia, has spread across Indiana since 1900. Two Galerucella spp. have been utilized as biological control agents for L. salicaria in Indiana since 1994. This study examines the impact of Galerucella spp. over an 8-10 year period at four Indiana wetlands. Galerucella abundance varied substantially over time but had low Spearman’s ρ at three sites (ρ = 0.21 to 0.40) due to rapid decreases following reduction in Lythrum. In contrast, hydrophyte species richness and percent cover were both correlated with time and had higher ρ (0.37 to 0.69) at three sites. The number of Lythrum inflorescences and stem density were reduced at all four sites, with inflorescences showing the strongest correlation (ρ = −0.46 to −0.78). Although variation was observed between sites, the introduction of Galerucella spp. resulted in significant declines in L. salicaria at each of the wetlands. Their impacts at these wetlands strongly suggest that Galerucella spp. can play a major role in controlling this invasive plant species.