Wintering stage: Larval inside seed head galls
Egg Stage: Egg-laying starts within three days after adult emergence. These eggs are laid around spring and summer time around immature florets of intermediate-stage by closed head buds with upright spines. Up to 270 eggs can be developed by female. The eggs are white and spiral-shaped
Larval Stage: There larval are form in a one-chambered, woody gall around each larva in seed head gall. Several larva occur inside each seed head gall.
Pupil Stage: Pupation stage always happens inside the galls.
Adult Stage: Adults start to come out in sprig and summer (over wintering generation). The insect is a black body with a yellow spot on the thorax. The wings have a dark cross band symbolizing the fly. Their total length of the male is 3 to 4 mm or .12 to .16 in. Females are a few millimeters longer. There length is 4 to 6 mm or .16 to .24 in including their ovipositor.
When They Take Effect:
They are at their destructive stage when they become a Larval. They were made to destruct yellow star thistle (Centaurea solstitialis). They attack mostly the seed heads of this extravagant plant or the interior. When they feed on this thistle they eat the developing seeds and this reduces down the plant by at least half. This may only have little impact on the plant.
When were they released?
They were first introduced to the United States in '84 in California.
They like to live in mostly cool climates in the higher elevations and latitudes, and near coastal areas. These areas are accommodate for flying areas. They are readily available.
How are they collected?
The weevil can be collected in several ways. Adults can be hand swept or hand picked from the plants causing some mortality. Collected seed heads can be collected in the late winter and may be moved to new sited for the adults emergence.
There has been known to be up to 12 galls per head recorded in California.
1) Rees, Norman, et. al., Ed., Biological Control of Weeds in the West, Western Society of Weed Science, in cooperation with USDA, ARS, MT Dept. of Agriculture, and MT State University, Color World Printers, Bozeman, MT, Feb. 1996.
2) Rees, Norman, et., al., Ed., Biological Control of Range land
Weeds in the Northwest United States, Manuscript/ Rough Draft. 1996