Insect detection and mean trap catch efficiency of two types of commercial probe traps, the Storgard WB Probe II (WB II) and Grain Guard (GG), were compared by sampling live beetles in the top ≤28cm of shelled corn stored in three round bins and two flat units. Unbaited WB II and GG traps were paired, and number of trap pairs among the five facilities ranged from 8 to 20. Insects were trapped between July and September 1990, and the trapping duration was 7 or 14 d (only in one flat unit). Adults of 13 species were detected by WB II traps, whereas 11 species were detected by GG traps. In general, insect species were more frequently detected and trap catches were higher in WB II traps than in GG traps. However, differences in insect detection and mean trap catch between the trap types were small. A double logarithmic model satisfactorily described (R2= 83%) the nonlinear statistical relationship between proportion of traps with adults and mean trap catches for both trap types. The progressively slower increase in proportion of traps with insects with increasing mean trap catches for both trap types can be explained by a purely probabilistic increase in the chance of a trap having more than one insect. This doublelogarithmic model is valuable for predicting mean trap catches, solely based on proportion of traps with insects. When validated with two independent data sets, obtained by sampling insects in shelled corn with WB II traps and in stored barley with GG traps, the predicted mean trap catches explained ≥84% of the variation in observed mean trap catches.