Wheat Stem Sawfly (Hymenoptera: Cephidae) Adaptation to Winter Wheat

The wheat stem sawfly, Cephus cinctus Norton, originally occurred in North American large-stemmed wild grasses. The pest adapted to spring-planted wheat, Trtiticum aestivum L., within 10 yr after cultivation began. Fall-planted winter wheat originally avoided attack, but was consistently heavily damaged by 1985. We reviewed the factors affecting the recent adaptation of C. cinctus to winter wheat. No changes could be detected in the seasonal phenology of winter wheat. Decreased acreage of spring wheat from 1921 to 1945 : reduced host availability. C. cinctus wasps are now emerging 20 d earlier than previously, and oviposition activity currently closely coincides with susceptible growth stages of winter wheat Larval cannibalism of eggs and younger larvae also provides natural selection for early season activity. Annual emergence of wasps from a population in wild grasses consistently begins later than in wheat.