Insect sampling/monitoring inside grain bins is time consuming, cumbersome during the summer heat in the headspace of grain bins, may require investment in costly sampling devices for sampling of grain, and involves a certain risk to employees. Thus, it is important to explore unbaited sticky traps on the outside of grain elevators as decision support tools for improved management of stored grain. In this study, we analyzed seven trap catch data sets of unbaited sticky trap catches on the outside of grain bins and corresponding probe trap catches in the upper level of the grain mass at three farm bins in 1991, with capacities ranging from 68 to 141 metric tons, and at two commercial steel bins in 1993 and 1994, with capacities of 5,400 and 6,800 metric tons. We used response surface regression analysis to analyze standardized trap catches of the rusty grain beetle, Cryptolestes ferrugineus, and showed that (1) from late June to late July, catches on unbaited sticky traps placed on the outside of grain bins preceded probe traps inside the bins by ≈3 d, which suggested immigration into bins; and (2) in late August, unbaited sticky trap catches on the outside of bins started to decrease, while probe trap catches inside the bins continued to increase until mid-September. We concluded that, from late June to mid-August, immigration of C. ferrugineus individuals into grain bins influences abundance in the upper grain layer, whereas later in the season, the two types of trap catches were only loosely associated. This study is consistent with results published elsewhere that immigration of C. ferrugineus into grain bins initiated shortly after wheat was loaded into the bins.