Sex-attractant traps were used to monitor the relative abundances of eight species of cutworm and army worm moths at 81 locations in a 13 000-km2 (5000-mi2) area of southern Alberta from 1978 to 1983. Clover cutworm (Discestra trifolii (Hufn.)), variegated cutworm (Peridroma saucia (Hbn.)), bertha armyworm (Mamestra configurata Wlk.), and Leucania commoides Gn. were monitored during spring and early summer, and redbacked cutworm (Euxoa ochrogaster (Gn.)), darksided cutworm (Euxoa messoria (Harr.)), pale western cutworm (Agrotis orthogonia Morr.), and army cutworm (Euxoa auxiliaris (Grt.)) during late summer and fall.
The ranking of moth catches among locations within years was highly consistent, indicating that the spatial pattern of abundance within the survey area remained stable during each flight period. The corollary is that differences in population levels among locations were being consistently detected. Most of the species also exhibited a considerable degree of consistency of pattern of abundance between consecutive years and to some extent over all years.
Estimates of the variability associated with individual traps, between duplicate traps, and among locations were obtained for each species. The within-location variability was always much less than the among-location variability, indicating that a meaningful measure of the relative population level at each location was being obtained. When abundance levels approached economic thresholds the likelihood of moth catches in duplicate traps being within 20% of the mean catch for a location was usually greater than 80%. Year-to-year differences in mean trap catches were frequently significant at the 95% confidence level and the monitoring system could detect relatively small changes in population level between years. Season cumulative trap catches are a composite measure of abundance and the mate-searching activity of males. Weather conditions that restrict male activity are also likely to reduce oviposition by females. Cumulative trap catches may therefore be closely correlated with realized fecundity.