Immigration of insects into on-farm stored wheat and relationships among trapping methods

Abstract

Relationships among numbers of insects trapped by unbaited flight and probe traps, and grain trier and deep bin cup samples were studied in 1991 in three farm bins in North Central Oklahoma. Placement of flight traps at the eaves of bins resulted in higher insect catches than at other positions. In the grain mass, insects were more likely to be in the central core during the first weeks of storage. Insects favored the center of the grain mass, but no significant differences were found among temperatures and moisture contents at the different regions sampled. Increasing numbers of insects with depth and length of storage time combined with the capture pattern of grain insects by flight traps indicated that infestation occurred after grain binning. The most abundant species were Cryptolestes spp., Tribolium spp., Rhyzopertha dominica (F.), Ahasverus advena (Waltl) and Typhaea stercorea (L.). Action thresholds (the insect densities at which managers need to control insect populations) for the number of insects in weekly probe trap catches were 7.35 for R. dominica, 720.14 for Cryptolestes spp., and 101.34 for Tribolium spp. when compared with estimates from grain trier samples, and 8.04,749.03, and 68.14 insects per probe trap, respectively, when compared with estimates from cup samples.