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

Larval infestations and adult counts of wheat stem maggot (Meormyza america na) were each compared among plots of intercropped spring wheat and alfalfa grown under high, intermediate, or low crop management intensity (CMI). CM I varied primarily in the amounts of nitrogen fertilizer, herbicide, and ti llage 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 t imes 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 gre ater 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. Th e number of adults collected was bimodal, peaking on the first and last sam pling dates each year. The interpretation of our results is discussed in th e context of cropping systems research.