Wheat stem maggot in spring wheat-alfalfa intercrops with different crop management intensities

Larval infestations and adult counts of wheat stem maggot (Meormyza americana) were each compared among plots of intercropped spring wheat and alfalfa grown under high, intermediate, or low crop management intensity (CMI). CMI varied primarily in the amounts of nitrogen fertilizer, herbicide, and tillage used. Infestation of wheat plants was measured from 1990 through 1993 as the percentage of white grain heads caused by larval feeding within the stems. Adult counts were made from sweep net samples within plots 3 to 5 times per year from 1991 through 1993. Larval infestation varied among years but not by CMI. The mean percentages of white heads in 1991 (2.0%) was greater than in other years (each less than or equal to 1.3%). Counts of adult M. americana differed among sampling dates within years but not by CMI. The number of adults collected was bimodal, peaking on the first and last sampling dates each year. The interpretation of our results is discussed in the context of cropping systems research.