Biology of Bull Thistle Seed Head Weevil, Rhinocyllus conicus Fröl. 1792 (Col.: Curculionidae) as a Biocontrol Agent of Bull Thistle Cirsium vulgare (Savi.) Ten. (Asteraceae) in Urmia Region.

Bull thistle Cirsium vulgare (Savi.) Ten. 1835 (Asteraceae) is a biennial weed that causes serious problem in grassland and cultivated areas. The biology of bull thistle seedhead weevil, Rhinocyllus conicus as a biocontrol agent of C. vulgare were studied in Urmia region. The results showed that, the R. conicus has a single generation per year and overwinter as adult. Adults emerge from hibernation at the end of May. They establish on host plant and feed on the leaves and soft stems of them. Adults mate from time to time throughout their life span. Then, fertilized females lay eggs below the capitula. Eggs are laid singly into a hole bored by female. The incubation period was 5-8 days in natural conditions. Upon hatching, the young larvae penetrate into the seedhead where they feed on receptacle tissue and developing seeds. Up to 6 larvae can develop in larger capitula. Larval development in natural conditions takes 27±5 days. Once larvae are mature, they consume and destroy the seedhead. Mature larvae make an egg shape and black color pupal cell in capitula and then pupate. The pupa completes its development in 9-14 days. Emergences of new adults begin in early July, then leave the capitula and search for suitable overwintering site. They reemerge in May of following year. The larvae of R. conicus were parasitized by two species of parasitic wasps namely, Baryscapus crassicornis (Hym.: Eulophidae) and Bracon armeniacus (Hym.: Braconidae). The species B. armeniacus is newly recorded from Iran.