You Are Here: Management Updates 2008 Archive August 13, 2008

Date: August 13, 2008
Category: Insects
Subject: Biological Control for Purple Loosestrife

A couple superintendents have asked me about purple loosestrife recently. As most of you know, purple loosestrife is an invasive plant species that has colonized many wetland areas throughout the Northeast over the past several years. It is a very pretty purple that quickly takes over an area. While it is pretty, it is invasive and it has forced out many native wetland plants in some areas.

Recently scientists have discovered some insects that feed on loosestrife and have released these insects in field settings with very good success. The questions that were put to me were: "Where do these insects overwinter?" and "How can I be sure not to interfere with the insects?"

Where do these insects overwinter?
Based on a quick web search, it appears that the most common biological control approach for purple loosestrife is one of two Chrysomelid beetles, Galerucella calmariensis or Galerucella pusilla. They have become established in more than 30 states and eight provinces where loosestrife is a problem.

The beetles spend the winter as adults in plant litter or "duff" in the area. They live several weeks after they emerge in the spring, feeding some on the foliage. They also lay one to ten eggs at a time on leaves or stems, beginning in late May or early June. Each female can produce as many as 400 eggs during her lifetime. The larvae then move to leaf buds and continue feeding, well protected from foraging birds. As they get larger, larvae then move out on to leaves and stems. (The larvae look like tiny caterpillars, with pale yellow bodies and very dark heads.) They pupate in mid June to mid July, and new adults emerge, feed for a short time, and then look for protective sites to prepare for winter. Occasionally a second generation may develop.

How can I protect these beetles?
Based on the information I found, the beetles overwinter in leaf litter and duff in the wetland area, so as long as you are not mowing in those areas (and you certainly shouldn't be!) and are not applying insecticides in the vicinity, you should not have any detrimental effect on the populations. You might try to avoid using broad spectrum insecticides near wetlands when the adults are moving actively - apparently May and July in southern New England.

Submitted by: Dr. Pat Vittum

DISCLAIMER - As always, it is the responsibility of the applicator to verify the registration status of any pesticide BEFORE applying it. Different states have different regulations as well. The author and the University of Massachusetts are not liable for any consequences of any pesticide "recommendations". Mention of any trade name is not to be considered endorsement of a product.

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