Dispersal of the wheat stem sawfly (Cephus cinctus)

The wheat stem sawfly, Cephus cinctus Norton (Hymenoptera: Cephidae), is a pest of wheat in the Northern Great Plains. In the mid-1990s the stem sawfly was found in wheat only in Scotts Bluff County. The sawfly can now be found throughout the Nebraska Panhandle, southeastern Wyoming, and eastern Colorado. The estimated annual loss in the Northern Great Plains, caused by the sawfly, is $350 million. More attention has been given to sawfly larvae than the adult in previous literature. The dispersal and distribution of the adult sawfly was characterized in three fields in the Nebraska Panhandle in 2014. Sweep net samples were taken biweekly through May and June. Peak sawfly emergence occurred through late May and early June. More than half of the adult stem sawflies were sampled from within the first 5 meters of the wheat border with the previous wheat field. Overall, males were more prevalent than females; however, at farther distances into the wheat fields and later dates in the flight period, sex ratios can be equal or reverse. An analysis using Taylor’s Power Law indicates that the adult stem sawflies have a clumped distribution in Nebraska wheat fields. No changes in the distribution were detected between males and females, or within the range of dates sampled during the flight period.