APPROVED BIOLOGICAL CONTROL AGENTS
Bradyrrhoa gilveolella, or the skeletonweed root moth, was recently approved for release. Adults emerge from exit tubes extending from the plant’s root in May and June. Females are capable of producing up to 300 eggs, laying them in the rosette crown or in the soil.
The eggs hatch in six to 10 days and the caterpillars penetrate the soil and begin to feed externally on the roots. The larvae feed both internally and externally on the root tissue, producing elongated tubes attached to the roots. These tubes are composed of frass, root fragments, sand grains, and latex from the plant. Larvae complete their development in 45 to 60 days in the tubes. Final instar larvae extend the exit tubes to the surface and pupate inside. Following their pupal stage, which lasts from seven to 10 days, adult moths force their way out of the capped exit tubes.
This insect is destructive in only the larval stage, when it destroys the cortical and vascular tissues of rush skeletonweed roots. The root feeding also exposes the plants to soilborne plant pathogens. Although establishment of this agent has not yet been confirmed, its preferred habitat (foreign collections) is sandy, granitic, or loose-textured soil.
Approved Biological Control Agents for release in Idaho: