It takes an army to tame purple loosestrife. In our case, that army’s soldiers are about a quarter inch long.
Purple loosestrife (Lythrum salicaria) is a Eurasian perennial plant that first reared its head in Morgan County in the mid-aughts. A single mature plant can produce hundreds of thousands to millions of seeds per year; once it is established, populations expand rapidly and are difficult to reverse. Originally, most of this beautiful but invasive species could be found along the banks of Warm Springs Run. In fact, the Warm Springs Watershed Association was initially established in part to attempt to control this scourge. Until 2 years ago there were very few purple loosestrife plants remaining along the Run or in surrounding wetland areas. Volunteers knew where each one was located, and we kept them in control using the methods noted above.
In 2024, everything changed. We saw large numbers of purple loosestrife in a wetland disturbed by the bypass. We knew that we had to try something different – Galerucella purilla and Galerucella calmariensis. Our research found that Canadian and US research agencies had done extensive host-specificity testing and approved these beetles’ release, confirming that they feed almost exclusively on purple loosestrife and closely related plants, and that they pose minimal threat to other wetland plants.
Galerucella purilla and Galerucella calmariensis lay eggs on purple loosestrife leaves and stems; when larvae hatch, they feed intensively on foliage, buds, and tender shoots. This repeated defoliation decimates the leaves, stunts shoot growth, and often prevents plants from producing viable flower spikes and seeds. Over time, chronic defoliation weakens root reserves, leading to smaller plants, sparse stands, and in some cases, the death of heavily attacked individual plants. Field studies in the Northeast and Midwest have documented dramatic reductions in purple loosestrife biomass after sustained beetle activity; some sites report more than 90-95% reductions over several years. The payoff? As loosestrife declines, native wetland plants recolonize and re-establish more diverse plant communities, which in turn support a wider range of wildlife.
Biocontrol with these beetles is best understood as a long-term ecological management tool to be used in large, heavily infested areas. At many sites, it takes three to five years before obvious declines in plant vigor and flowering are observed, and a decade or more to reach the point where loosestrife biomass has been substantially reduced. Most practitioners now see beetles as one component of integrated management rather than a stand-alone solution. Accordingly, WSWA still uses hand pulling and selective herbicide application for small, isolated patches.
Grant funds from the WVDEP Save Our Streams program allowed the watershed association to release purple loosestrife beetles in 2025. Encouraged by the highly evident efficacy of this method of control, we purchased more beetles. They are about to be released, in May 2026.
We’re deploying the beetles; now we need our neighbors. Watch for purple loosestrife and ask your neighbors to do so. If you see purple loosestrife, especially along the stream, contact us via our website to inform us of what you’ve seen, and let our tiny army do the rest.