Imported longhorned weevil injury: Soybean rows destroyed by imported longhorned weevils, Calomycterus setarius, near Mapleton, Iowa [top]. Weevil populations along this field edge were abnormally high. Soybeans defoliated by imported longhorned weevils [middle]. A hand-full of weevils collected from soybean with a sweep net [right].
The imported longhorned weevil, Calomycterus setarius, is a parthenogenetic insect, with only females being produced, and does not fly (Johnson 1944). This allows for explosive populations to build up when conditions are right (e.g., observed in Rice and Pilcher ).
The imported longhorned weevil is rare in Iowa soybeans, but they have been reported here since 1943 (Rice and Pilcher 1998). This species is originally from Japan and was first recorded in the United States in 1929. It is a parthenogenetic insect, with only females being produced. It can not fly (Johnson 1944) and moves to new locations either by crawling or being transported by humans on farm equipment, baled hay, or horticultural stock. Larvae are known to feed on roots of alfalfa, clover and several species of grasses. Very large populations of adults in Iowa have been observing moving into soybeans from adjacent bromegrass waterways or fields (Rice and Pilcher 1998).