Purple Loosestrife Biocontrol

Purple loosestrife is a 'List A Species' in Colorado which means that it is scheduled for eradication and biological control is an inappropriate control method. More information on Purple Loosestrife.

The Colorado Department of Agriculture does rear biocontrol agents for purple loosestrife as part of a nationwide cooperative program. Hylobius transversovittatus is a large weevil that develops within the roots of purple loosestrife. They require one to two years to develop on plants but at the Insectary they are reared on an artificial diet where they can go from egg to adult in just ten weeks. These weevils have been shipped from Colorado to new homes in several other states.

These insects are not shipped out for general use.
 

What is purple loosestrife?


Purple loosestrife, Lythrum salicaria, is a perennial, herbaceous weed that is commonly found along waterways and throughout wetland habitats.  It was introduced from Europe during the late 1800’s either in ship ballasts or as an ornamental.  It is found in Colorado in limited areas and, thus, is legislated for eradication only.

How do I recognize purple loosestrife?


Purple loosestrife is a large plant growing up to 3m tall.  The inflorescence is a spike of numerous, showy magenta flowers set in clusters.  Each flower has 5 to 7 petals with a small yellow center.  Stems are woody and square shaped with 5 or 6 sides.  Purple loosestrife is an abundant seed maker as one mature plant can produce several million seeds.  It is sometimes confused with native fireweed, Chamerion angustifolium, among others.

What are the effects of purple loosestrife?


Once established purple loosestrife crowds out native vegetation, often creating a monoculture.  In addition to the loss of native biodiversity, purple loosestrife harms waterfowl nesting habitat and can have negative impacts on some amphibians and algal communities.  It also reduces water flow and quality, inhibits transportation and degrades hunting, fishing and recreation areas.

Biocontrol of purple loosestrife:


The Insectary is currently working with a root mining weevil, Hylobius transversovittatus.  This is a large, reddish brown weevil, 10 to 14mm in length. This weevil is nocturnal and long lived as an adult, 2 to 3 years or longer.  The larval stage of the life cycle does the most damage to the plant as they mine the stems and roots.  This was the first biocontrol established in the United States and Canada for purple loosestrife.  Partnerships from neighboring states such as Utah, Idaho, Oregon and Washington have allowed the CDA to rear this insect for release. 

Rearing methods:


Unlike other projects at the Insectary, H. transversovittatus is raised on artificial diet.  This method has been developed to facilitate mass rearing in a much shorter time frame. In lab culture, Hylobius eggs are laid in the floral foam housing a bouquet of purple loosestrife stems.  These eggs in the petri dish were recovered from this floral foam and washed and sterilized to be placed on the artificial diet (A). The artificial diet for rearing Hylobius consists of Soy protein, corn cob grit, vitamins and antibiotics to name a few.  Once the egg is placed in a small hole on the top of the diet, the larvae begin feeding on this mixture.  After pupation, the adults are collected from the diet cup and either placed back into the egg laying cage or shipped to other states for release (B). This is the adult Hylobius transversovittatus.  In nature it can live as an adult for 2 to 3 years (C).

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