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Weed control, management, ecology, and minutia
by Juan Medrano
on May 5, 2021 at 4:14 PM
How do you grow and propagare the star thistle rosette weevil?  
Please help me understand the life cycle: adults emerge from hibernation in early spring (April), at this time do they mate and lay eggs on the rosette roots and larva developed in the rosette roots? Then larvae pupate and adults emerge in June. Where do adults go in hiding and hibernation? Are adults eating at this time as they develop?  
Thanks, this is fascinating and would like to understand it better.
by Scott Oneto
on May 14, 2021 at 4:56 PM
Thanks for the question Juan. The yellow starthistle adults emerge from hibernation in the early spring and feed on yellow starthistle leaves. Females lay eggs in the leaves of rosettes from late March to early May in central Italy and we are expecting to see a similar timing in much of California. Eggs hatch in about 10 days at room temperature, and first instar larvae mine in the leaf blade and down the petiole. Larvae feed primarily in the root crown (upper part of root stem), complete development in about two months, and pupate inside the plant. Adults emerge in June, feed on yellow starthistle leaves for a few days then disappear. They are thought to aestivate (become dormant during the summer or dry season) and hibernate (overwinter in a dormant state) in secluded places, and adults have been found under tree bark in July. Newly emerged females are in a state of reproductive dormancy, and although they mate, they are not able to lay eggs until completion of hibernation. In  
the spring, after feeding for 1–2 weeks, females lay a few eggs per day for 1–2 months before dying.  
In terms of propagating the weevil, we hope that the weevils that are currently being released will reproduce and over the course of a few years these sites will be used as a nursery where insects can be collected and moved to new locations.
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