Linda Wilson, University of Idaho, Bugwood.org

Linda Wilson, University of Idaho, Bugwood.org

Purple Loosestrife

APPROVED BIOLOGICAL CONTROL AGENTS


Galerucella spp.

Galerucella spp., or the loosestrife beetles, may overwinter in the soil and surrounding vegetation. The adults typically emerge from hibernation, mate, and lay eggs from April through June. These agents are capable of producing two generations per year with new adults emerging and dispersing to additional locations in July and August.

Female adults lay eggs from May to June and again from August to September. Females can produce 300 to 400 eggs, laying up to 10 eggs per day in groups of three to six on stems, leaves, and leaf axils. Larvae and adults feed upon young buds and leaves, producing a “shotgun” appearance in the leaf material which, with heavy defoliation, skeletonizes and kills the plants.

These insects are best collected once egg-laying has begun in the early spring. They can be collected with sweep nets or hand-picking and should be released in groups of 250 to 500 adults.

Hylobius transversovittatus

Hylobius transversovittatus, or the loosestrife root weevil, can overwiner as an egg, larva, pupa, or adult. Adults typically emerge in mid-to late summer and may live up to three years with females depositing about 300 eggs over a two-year period. One or two eggs are laid daily from June through August. The eggs are mostly deposited in the soil, but some are inserted into the stems just above the soil surface. The eggs hatch in 11 days and the larvae are normally present from August through June of the next year.

Larvae mine the roots and feeding tunnels are packed with light brown frass. Pupation occurs within the root during late spring to early summer. Both the adult and larval stages are destructive, but their impact depends upon plant root size, attack intensity, and duration.

This agent’s ideal habitat is a site without prolonged flooding, but it is able to withstand a wide range of environmental conditions. These weevils are easiest to collect at night, and can be reared with an artificial diet or from infested roots. When Hylobius is paired with Galerucella, their combined impacts seem to be very deleterious to purple loosestrife plants.