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weevils were released on 50 acres heavily infested with thistles in Warren County in 1969. Extension agent Gary DeOnis reported that nothing much happened until 1973 but added that three years later, it was hard to find over a couple of hundred thistles on the entire 50-acre tract.
Adult weevils hibernate from late August until early May. when the thistle starts forming a flower head. The female lays 150 to 200 eggs protected by a mud daub covering on the underside of the plant. The eggs hatch as larva in early June and burrow into the center of the thistle, feeding on seed tips. Once the tips are eaten, the seeds can't germinate and the plant dies without spreading.
Weevils will never eat all the thistles in Rappahannock County. Stability, not complete eradication, is the goal of the biological control program. Once the weevils are established, the incidence of thistles will decrease while the weevil population grows until there are only a few pockets of thistles left. Then the number of weevils will decrease in response to the limited food supply. According to Extension specialists, weevils have met with the greatest success to date in Pulaski County, where a 95 percent control of thistle growth was achieved on a thousand-acre project.
Besides the little muddaubed eggs on the underside of thistle flowers, weevils leave other tell-tale signs of infestation. As the flower begins to dry, the center portion that goes to seed developes a tuft or protrusion that extends beyond the rest
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