Phenological synchrony of Eustenopus villosus (Coleoptera : Curculionidae)with Centaurea solstitialis in Idaho

The phenological synchrony of Eustenopus villosus (Boheman) with its host, yellow starthistle, Centaurea solstitialis L. (Asteraceae: Cardueae), was s tudied in Idaho in 1995 and 1996. Field plots were observed for adult weevi l activity periodically throughout the growing season, and yellow starthist le capitula were examined for adult feeding damage, oviposition damage, and larval development. At the study site, weevil phenology was well synchroni zed with C. solstitialis. Im mature capitula, fed upon by adults, were abun dant when E. villosus began to emerge in late May. During both years, the n umber of weevils and capitula increased throughout June. Adult females fed on capitula for about 2 wk. Weevil ovary dissections revealed that ovaries were mature after a 2-wk period of feeding. The development of mature capit ula during late July corresponded to the initiation of oviposition. Eusteno pus villosus, unique among the phytophages introduced for C. solstitialis b iological control, attacks four plant stages resulting in observable impact to buds. Damaged buds either died or became distorted. Weevil feeding dama ge on young and mature capitula may make this insect a highly effective con trol agent.