Species and abundance of cutworms (Noctuidae) and their parasitoids in conservation and conventional tillage fields

Abstract

The density of cutworm larvae (Noctuidae) was determined in fields under minimum and conventional tillage practices in Manitoba, Canada. Larval densities were based on area samples taken in the fields every spring from 1983 to 1990. During this period cutworm densities were well below the level of economic damage to crops. The results of the study provided information on the effects of tillage practices on cutworm abundance and species diversity during a period of endemic populations. Larvae were more abundant in fields under minimum tillage than conventional tillage practices. The most damaging pest cutworm in Manitoba, Euxoa ochrogaster (Gn.) (redbacked cutworm), two species often associated with this species in outbreaks, Euxoa messoria (Harr.) (darksided cutworm), and Feltia jaculifera (Gn.), and a non-pest species, Lacinipolia renigera (Steph.) (bristly cutworm), made up 63% of the larvae from minimum- and 51% of those from conventional-tillage fields. There are significantly more cutworm larvae in minimum-tillage fields, owing to larger numbers of L. renigera and other non-pest species, than in conventional-tillage fields. The percentage parasitism of cutworm larvae was not significantly different between tillage practices. Cutworm abundance in a field was related to the crop of the previous year, with larger numbers of larvae associated with broadleaf crops than with cereal crops. Different species had different patterns of abundance during the 8-year study and different relationships to tillage and crop. Minimum-tillage practices were not related to increased crop loss from cutworms during the study period, but were associated with greater species diversity of both cutworms and their parasitoids. This greater diversity was accompanied by less interfield variability in cutworm numbers, suggesting a more stable ecosystem in which outbreaks would be less common.