Biological Control with Galerucella Beetles

By Emily Stinneford, Summer Program Steward & Dillon Mulhern, Preserves Manager

In collaboration with Maine Coast Heritage Trust, KELT raised Galerucella beetles as a biological control agent for the invasive plant purple loosestrife (Lythrum salicaria) - a widespread invasive plant that degrades the health of wetlands and shoreline habitats by outcompeting native plant species.

*Galerucella beetles at Woodward Point.*

KELT and MCHT collected two species of beetle from an established population in southern Maine and propagated them at Woodward Point in Brunswick using transplanted loosestrife plants in pots. For two months, the beetles fed on the loosestrife and swiftly multiplied their population.

On July 12th, 2024, we determined the beetles had reproduced sufficiently. With well-fed Galerucella beetles covering the potted purple loosestrife plants, KELT staff and stewards carefully relocated the pots to the freshwater marsh at Center Point Preserve in Bowdoinham. A preserve whose marshy shores unfortunately host a healthly population of loosestrife. The released beetles will now feed on the purple loosestrife infestation in the preserve, hopefully lessening the impact this invasive plant has on local ecosystems.

What is Biological Control?

Biological control is a subset of integrated pest management. The process utilizes an invasive species’ natural predators, often from their native range, to control populations of the invasive species and is orchestrated by humans. This is different from natural control, which does not require human intervention and is reliant on environmental factors or native predators in the local environment to control pests. Biological controls are specific to the invasive species they are meant to reduce. Various testing agencies (USDA Agricultural Research Service, Cornell University) have concluded Galerucella beetles do not negatively impact native species.

“The Galerucella beetles have proven to be the most successful biocontrol agent to combat purple loosestrife due to their effective reproductive process and ability to damage the plant at all stages of its life cycle. ”

*Galerucella beetles inflict significant damage to the purple loosestrife leaves, as seen here.*

**Why Galerucella Beetles?**

The Galerucella beetles have proven to be the most successful biocontrol agent to combat purple loosestrife due to their effective reproductive process and ability to damage the plant at all stages of its life cycle. Galerucella cannot complete its life cycle on anything other than Lythrum salicaria (loosestrife). The beetles feeding activity on purple loosestrife reduces the density of the species and allows native plants to compete with this troublesome invasive plant.

The damage these beetles can inflict on the invasive plant is extensive! Adult beetles chew through the leaves, while larvae feed on the photosynthetic tissue, leaving only the cuticle membrane and veins of the leaf. In dense beetle populations, plants can be entirely consumed except for the stalk and stems!

Why Center Point Preserve?

The Galerucella beetles have shown real promise both in the state of Maine and other northeast states in controlling large populations of purple loosestrife that can displace native species (especially in a freshwater marsh, like at Center Point, which is full of state-listed and globally rare species). Purple loosestrife is beginning to outcompete within the marsh. Releasing biocontrol beetles here will prevent native plants from being displaced, ensuring the long term stability of these vital ecosystems.

*The freshwater marsh at Center Point Preserve. It’s a part of Merrymeeting Bay, one of only four inland river deltas in the world!*

What is the process?

Land Trust staff and stewards collected purple loosestrife plants and Galerucella beetles from an existing population identified in southern Maine. This collection occurred in early June, very early in the morning - when it was colder and the beetles were less mobile. When disturbed the beetle's instinct is to drop from the plant, so they were collected by swiping them into small bottles. Not complicated - just effective!

The root systems of several multi-stemmed purple loosestrife were dug out of the ground and thoroughly washed to remove seeds and predatory insects that could threaten the Galerucella. They were then repotted and placed in plastic wading pools. We required loosestrife with abundant growth, so we chose large plants that had not been previously disturbed by beetles. The repotted plants were placed at Woodward Point in direct sunlight and several inches of water, to simulate a wetland environment.

*MCHT Stewards wash root systems of transplanted loosestrife.*

*MCHT Stewards prepare a simulated wetland environment to host the loosestrife and beetles in kiddie pools!*

Beetles were introduced once our loosestrife plants were at least 18 inches tall. Once beetles were introduced to the loosestrife population, we placed suspended nets over the plants, securing them with clothespins on a clothesline overhead. The nets kept our growing population of beetles close to home!

In mid-July, once the beetles had reproduced and the population was significant, we began the relocation process. Our stewardship team first collected as many loose beetles as possible, as some had escaped the netting. Once these beetles were contained in small bottles, we secured all loosestrife plants in netting.

*(L to R): Summer Land Stewards Helen and Lelia with Preserves Manager Dillon secure netting to the host loosestrife plants.*

*Preserves Manager Dillon prepares to move the host loosestrife plants and beetles to their new home in Center Point Preserve.*

All beetles and plants were transported to the freshwater marsh at Center Point Preserve, where they were released in two main sites, each containing large populations of purple loosestrife. These sites were on the upland edge to protect the beetle population from flooding as the marsh is influences by the tides. The collected beetles in bottles were released, and the nets were removed from all plants.

Galerucella produce and release pheromones and are more productive when density is high, so clumping the pots close to one another is more helpful than dispersing them widely. The plants will remain until the end of the growing season, as there are most likely pupae in the soil that will develop and emerge.

As the Galerucella populate in their new home, we hope to see significant reduction to the purple loosestrife population on site!