Tag Archives: biocontrol

Lose the Loosestrife: Beetles for Biocontrol

Purple loosestrife (Lythrum salicaria) is an invasive plant from Europe and Asia that can overcrowd native wetland plants. It is easily recognized by its tall and showy purple spike of flowers in the summer, lance-shaped leaves and square stems. As an invasive species, it lacks its natural predators and can spread quickly, producing as many as 2.7 million seeds a year.

Loosestrife flower, photo by A McGinnis
Purple loosestrife flower spikes at Silver Lake State Park. Photo by Amy McGinnis

Wetlands are rich habitats that support a diversity of plant, insect and animal species, such as marsh marigold (Caltha palustris,) twelve-spotted skimmer dragonfly (Libellula pulchella,) painted turtle (Chrysemys picta,) green heron (Butorides virescens.)  The introduction and spread of purple loosestrife has resulted in the loss of native plant and animals that depend on wetland habitats. In addition, purple loosestrife limits the growth of rare plants and can clog drainage ways and ditches, negatively affecting adjacent land and crops.

Loosestrife in bloom, photo by Amy McGinnis
Purple loosestrife plants in bloom at Silver Lake State Park. Photo by Amy McGinnis, State Parks

Since purple loosestrife grows in wetlands, methods to control this plant and promote native biodiversity aren’t always easy. Small young infestations can be removed using hand tools, but care must be taken to dig out all of the root portions to avoid regrowth. This may not be feasible for larger, more established infestations. The flower heads cut be cut, bagged and disposed of to prevent seed production and the spread of this plant. Chemical herbicides can be utilized by licensed applicators that follow strict protocols to avoid contaminating water bodies and non-target native species. However, there is an easier way to fight this invasive: biological control or biocontrol. Biocontrol is the control of an invasive species by introducing a natural predator of that species following very specific federal and state regulations and testing to make sure there will be no other negative impacts on the ecosystem. In this case, the biocontrol is the small purple loosestrife beetle, a beetle of the genus Galerucella. These are native to Europe and Asia and feed on purple loosestrife in its native range, keeping the plant in check.

Scientists must thoroughly test any biocontrol species to make sure they only affect the target invasive species and don’t negatively impact native species. In the U.S., studies have shown the beetles to be very host-specific, feeding and reproducing predominately on purple loosestrife. The beetles do not completely eradicate purple loosestrife, but they suppress the plants’ growth and ability to reproduce by feeding on its stems, buds and leaves. Thus, they reduce the plants’ dominance and impact within the ecosystem.  Since 1992, biologists working under state and federal permits have released millions of these beetles at numerous sites across the northeast, including at several New York State Parks, such as Silver Lake State Park in western NY.  In NY, the Department of Environmental Conservation continues to monitor the numbers and effectiveness of the beetles and to ensure there are no unforeseen problems.

The beetles are released in the summer when loosestrife is actively growing. They overwinter in the soil near the host plants and emerge in the spring to reproduce, with females laying eggs from May to June. When they hatch, the larvae feed on the loosestrife’s young growth and work their way down the plant where they eventually enter the soil to pupate. They emerge as adults in the summer and the cycle continues. Though they are not strong fliers, occasionally the beetles have been found 10-12 miles away from the initial release site.

Release sites for the beetles are determined by the dominance of purple loosestrife. These sites usually have a high percentage of loosestrife plants where hand removal of them is difficult. Biologists must submit an application to the Department of Environmental Conservation to justify the need for the beetles and receive a permit. The number of beetles depends on the size of the purple loosestrife infestation. Silver Lake State Park is one location where the beetles have been used as a biocontrol for this invasive plant. Silver Lake has an approximate 40 acre wetland with a purple loosestrife population of about 15%. In 2010, 800 Galerucella beetles were released in an effort to control the loosestrife. One meter by one meter plots were established in order to monitor the survivorship of the beetles and the defoliation, or the loss of leaves, stems and flowers, of the plants where the beetles have fed on them. Each summer after the beetles have emerged, the plots are assessed to determine the effectiveness of the beetles and if any more should be released. This is done by looking at the number of loosestrife plants that are defoliated (eaten, not flowering) vs. the number that are flowering, as well as the number of beetles that are seen. More beetles have been released at Silver Lake State Park since the initial 800 in 2010; the purple loosestrife plants have remained contained to that area and their growth has been restricted.  In 2016, State Parks biologists expanded the program to Letchworth State Park.

The extent of purple loosestrife has declined dramatically in areas with this biocontrol. It is unlikely that the beetles will eliminate purple loosestrife populations entirely. The hope is that as more Galerucella beetles are released across the state, the invasive loosestrife will be diminished, making room once again for the native flora and fauna at these sites.

Beetle on loosestrife at Silver Lake SP, photo by A McGinnis
Galerucella calmariensis beetle on a purple loosestrife leaf at Silver Lake State Park, photo by Amy McGinnis, State Parks

Post by Amy McGinnis, State Parks

Featured image, Galerucella calmariensis beetle on a purple loosestrife, by Amy McGinnis, State Parks

Invasive Species Spotlight: Monitoring for Hemlock Woolly Adelgid

Hemlock Woolly Adelgid appears as white fluffy balls on the underside of hemlock branches during the cooler months.
Hemlock Woolly Adelgid appears as white fluffy balls on the underside of hemlock branches during the cooler months.

Hemlock Woolly Adelgid (HWA) is a tiny, invasive insect which kills hemlock trees in a matter of 6 years. Please see the previous post on HWA for more information. The insect was introduced in Virginia in the early 1900’s, and has steadily spread since then. New York state contains all stages of HWA infestation. There are heavily infested areas like the lower Hudson Valley, which have harbored HWA for 20+ years and contain increasing numbers of declining and dead hemlocks. Moderately infested areas include the Finger Lakes, where some areas have HWA and some do not. Several HWA early detections were made in Western NY’s Allegany State Park by dedicated volunteers, trained by Park staff to survey for the insect. Allegany just has a few isolated patches of HWA, and State Parks is working to keep those patches small. So far, the Adirondacks have escaped infestation, but they are not immune.

map
This map shows the spread of HWA by township since 1987. Map from http://www.dec.ny.gov/animals/7250.html.

How do we know all this information? The first step in determining if HWA is present is simply to look for it. Surveying for HWA takes diligence; the insects’ most visible life stage is the egg sac, which is present in the fall and winter. A hand lens is necessary to identify the tiny adults in the summer. Primarily through grant funding and volunteers, Parks has surveyed for HWA in 20 State Parks, and that number increases every year.

Survey technique demonstration for volunteers in Allegany State Park.
Survey technique demonstration for volunteers in Allegany State Park.

After surveying, maps are created and examined and hemlock stands are prioritized for treatment. Prioritization is a rigorous process which includes collaboration with state and local experts. These experts ask questions like: Do dead/dying hemlocks pose a health and safety risk here? Is there an area of ecological significance, for example, an old growth stand or is there an insect or animal present which is dependent on hemlocks? Will the loss of hemlocks create a significant, negative change to aesthetics? Is this an area of early detection, where treatments could make a big difference?

Mark Whitmore, of Cornell University, gazing at a hemlock in serious decline at Minnewaska State Park Preserve.
Mark Whitmore, of Cornell University, gazing at a hemlock in serious decline at Minnewaska State Park Preserve.

Treatment for HWA does exist. Parks has chosen our methods through regular consultation with experts, based not only on what works, but what has the least impact on the environment. Pesticides are carefully sprayed onto the bark of hemlock trees, in the spring or early fall. The pesticides are taken up rapidly through the bark and into the tree, where hemlock’s circulation system takes it throughout the tree, to all the little branches. The HWA will not survive on treated hemlocks for the next 7 years. While this is certainly not a permanent solution, it does buy us much needed time.

In conjunction with these treatments, Parks is also releasing biological control beetles. Biological control insects have an extensive approval process which can take a decade or more through the USDA. Many states have biological control review processes as well, including NY. These processes are designed to assess and evaluate the insect and its host specificity, the reproductive and cross breeding potential, and other factors. If, and only if, the insect is passes the host specificity and other tests, is it approved for release. Many biological control insects have been explored for control of HWA, one showing some promise is Laricobius nigrinus. These biological control beetles feed exclusively on HWA, and while they will not eliminate their food source, they can keep HWA populations in check so they are no longer killing hemlocks. While this is the ideal end result, it can take a decade or more before this is attained. Releasing a few hundred L. nirginus against millions of HWA means we need to buy time, through the use of pesticides, as these beetles work to increase their populations to levels where they can match HWA and keep it in balance.

Invasive insects are notoriously difficult to contain. While we may never stop the onward march of HWA, we can reduce the negative impacts of hemlock loss in specific areas through human intervention.

Sign up for an upcoming iMap Invasives training to learn how to report HWA when you spot it in State Parks’ forests.

Post and photos by Alyssa Reid.