Unbaited sticky traps were placed on ropes in the four cardinal directions and at different heights on the outside of commercial steel bins containing stored wheat. Weekly trap catches of the rusty grain beetle, Cryptolestes ferrugineus (Stephens), were examined. The number of traps per steel bin varied due to differences in dimensions, and three height classes were established, but there was no significant difference in trap catches of C. ferrugineus among height classes. Significant yearly and between-steel bin variation was found, and these effects were removed before using a response surface regression analysis to determine how well two time variables (daylength and day number) and three weather variables (minimum and maximum temperature and precipitation) could explain the seasonal variation in C. ferrugineus flight activity. These variables were used in separate analyses of C. ferrugineus trap catches in the four cardinal directions and from the three height classes (12 separate analyses). The most robust model fit was obtained when using a subset representing 208 C. ferrugineus trap catches from the northern side at height class 3 (traps s placed at least three-quarters of bin height). The full model of the two time variables and three weather variables explained 48% of the variance in this subset of trap catches, whereas a model based on weekly means of daylength and minimum and maximum air temperatures explained 40% of the total variance in C. ferrugineus trap catches. The relative trap catch response to daylength and minimum and maximum air temperatures was evaluated. High beetle flight activity around grain bins may indicate a high risk of insect infestation of stored wheat, and the presented model can therefore be used to determine time periods with high risk of beetle immigration into commercial steel bins.