Purple Loosestrife Bioconrol Frequently Asked Questions

Frequently asked questions about the Biological Control Project for the management of Purple loosestrife, Lythrum salicaria.

In recent years I have seen a dramatic reduction in Purple loosestrife populations in those areas where the two leaf-feeding beetles (Galerucella pussilla and G. calmariensis), have been released, but more importantly I have seen these beetles spread to other areas away from their site of introduction. In general, it takes time. It may take anywhere from a couple of years to up to10 years, to achieve satisfactory results. The majority of the sites where the Department of Agriculture has released beetles have taken approximately 5 years to reach a level of satisfactory control.

In general, these leaf-feeding beetles cause a significant amount of damage to the foliage of Purple loosestrife thus causing severe stunting and preventing or inhibiting flower/seed production. However, the beetles do not cause enough damage to completely destroy the plants since that would eliminate their sole food source.

The stunted growth of the Purple loosestrife can then allow native species to reestablish themselves and rebuild the ecosystem back to their natural state. Although Purple loosestrife still lurks in amongst the native plants they are usually kept in check by the beetles so they do no have a subsequent population explosion.

Below are the answers to some of the more commonly asked questions:

Do these beetles feed on other plants when Purple Loosestrife populations become depleted?

What type of food do the larvae of these beetles eat?

Do these beetles have any known native enemies in New Hampshire?

To what extent do these beetles compete with other species?

Do these beetles feed on other plants when Purple Loosestrife populations become depleted?

The two insects, Galerucella calmariensis and G. pusilla, used for this project are leaf-eating beetles that are native to Europe. In the late 1980's, the USDA conducted host specifity tests of 120 European insects that feed on loosestrife and found four that solely feed on loosestrife. The Galerucella beetles will not eradicate the loosestrife entirely, but they will significantly stunt the plants to an extent that prevents them from flowering and thus they do not produce seed. In addition, the stunting allows native wetland vegetation to gain an edge and outcompete the loosestrife over time. If the loosestrife is significantly damaged, then the beetles will either perish or move to another area with loosestrife. There have been reports of the beetles eating native whorled loosestrife, but since my involvement with the beetles dating back to 1996, I have never seen this occur.

What type of food do the larvae of these beetles eat?

The larvae as well as the mature beetles all feed on the foliage of the loosestrife so there is always a continuous bombardment of attacks of the loosestrife throughout the growing season.

Do these beetles have any known native enemies in New Hampshire?

Any large predatory insect or spider has the ability to prey upon the beetles, but this is not generally an issue that would cause any concern.

To what extent do these beetles compete with other species?

Since loosestrife has no native natural predators, the introduction of the Galerucella beetles does not pose a threat to other species.

For more information on the Purple loosestrife Biocontrol Program, contact Douglas Cygan at (603) 271-3488 or email doug.cygan@agr.nh.gov.