PLANTING DATE INFLUENCES PREHARVEST INFESTATION OF DENT CORN BY ANGOUMOIS GRAIN MOTH (LEPIDOPTERA, GELECHIIDAE)

Preharvest infestation of dent com, Zea mays L., by Angoumois grain moth, Sitotroga cerealella (Olivier), was measured for com planted on different dates in central Kentucky. Com was planted on three dates in 1990 and 1991: (1) the conventional planting date of mid- to late May, (2) 3 wk earlier, and (3) 3 wk later. One location was planted in 1990 and three locations in 1991. Com was sampled on three dates at 3-wk intervals from late September to mid-November. Infestation was measured at sampling time and again after a 5-wk incubation in the laboratory. Infestation decreased linearly with planting date, with essentially zero infestation evident at sampling time for late-planted com, and increased linearly with sampling date. Emergence of adults after incubation of samples in the laboratory revealed that infestation rates were considerably higher than initial infestation assessment indicated. This measure of latent infestation decreased with planting date only for corn in early stages of infestation and generally increased with sampling date. Correlation between moisture content of corn and infestation rate was significant but not particularly strong. Moisture content was apparently a major determinant of infestation, however; corn >31% moisture content was virtually uninfested. The results suggest that earlier planting increases the risk of infestation by Angoumois grain moth, as does leaving corn in the field after it has dried below a critical moisture content.