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Biological Control : A Guide to Natural Enemies in North America Anthony Shelton, Ph.D., Professor of Entomology, Cornell University

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Pterolonche inspersa
Lepidoptera: Pterolonchidae

by R.F. Lang, USDA-APHIS-PPQ, Bozeman Biocontrol Facility, Forestry Sciences Laboratory, Montana State University, Bozeman, MT 59717- 0278.

The root-boring moth, Pterolonche inspersa a native moth of Europe, was approved for release in 1986. P. inspersa has been released in Colorado, Montana, and Oregon. There is no known establishment in the United States of this biocontrol agent.


The P. inspersa adult is a light brown moth measuring 20 mm wingspan and 8 mm in body length. There are no distinct markings on the wings.


Spotted and diffuse knapweed are weed species that can be found throughout the northern tier of states and as far south as Nebraska and Virginia. These highly competitive weed species favor and establish quickly on disturbed sites and overgrazed rangeland. Both weeds will invade well established grassland communities and out compete the native vegetation. The release of P. inspersa is part of a program to introduce a complex of spotted and diffuse knapweed enemies to help control these weeds.

Pests Attacked

P. inspersa prefers diffuse knapweed ( Centaurea diffusa). The host specificity tests found the moth limited to a few Centaurea spp. none of which are endangered or economically important. The two native Centaurea spp., C. americana and C. rothrockii, are annuals and senesce and die when P. inspersa is laying eggs.

Life Cycle

P. inspersa produces one generation per year. Adults emerge in July and early August. The larvae overwinter in the roots of the knapweed plants. Mating and egg laying commence soon after emergence. The larvae upon hatching penetrate the root crown and begin to feed in the root. They spin a silken tube and feed from within the tube. The tube protects the larvae and provides an exit for the emerging adult. The adult lives up to fifteen days.

Pesticide Susceptibility

Not known

Commercial Availability

P. inspersa is not yet available from public or commercial sources.


Infested diffuse knapweed plants can be recognized by the silken tubes around the crown of the rosette. P. inspersa larvae cause considerable root damage and as a result the plants are stunted and produce fewer flowers. The infested root becomes spongy and the storage capacity is reduced. The roots are prone to bacterial, viral and fungal infections.


Sites that are chosen for P. inspersa releases should not be disturbed for at least ten years by development and pesticide use.


Campobasso, G., R. Sobhian, L. Knutson, A.C. Pastorino, and P.H. Dunn. 1994. Biology of Pterolonche inspersa (Lep.: Pterolonchidae), a biological control agent for Centaurea diffusa and C. maculosa in the United States. Entomophaga 39: 377-384.

Dunn, P. H., S.S. Rosenthal, G. Campobasso, and S.M. Tait. 1989. Host specificity of Pterolonche inspersa (Lep.: Pterolonchidae) and its potential as a biological control agent for Centaurea diffusa , diffuse knapweed, and C. maculosa , spotted knapweed. Entomophaga 34: 435-446.

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Pterolonch inspersa adult moth.

Pterolonch inspersa adult moth.

Photo: R.Richard

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