Stored-grain insect population commingling densities in wheat and corn from pilot-scale bucket elevator boots

Grain elevator boot and pit areas facilitate the commingling of insects with the grain moving through the elevator leg. A removable boot was developed to facilitate residual grain removal and preservation in the boot and to quantify the commingling magnitude as a function of stored-product insect density. This study included two species that develop inside kernels, Rhyzopertha dominica and Sitophilus oryzae, and three species that develop outside kernels, Tribolium castaneum, Oryzaephilus surinamensis and Cryptolestes ferrugineus. The removable boots were loaded with infested residual grain and remained undisturbed for 0, 8, 16, or 24 weeks (wk). After each time point, uninfested grain was transferred through the infested boot. The adult beetles that commingled with the clean grain were sifted and counted. Further, the commingled lots were examined after 8 wk for adult progeny. The insect densities in the infested bucket elevator leg boots affected the insect densities transferred through the elevator leg to other locations. The insect density in clean wheat or corn transferred over infested boots was 1 insect/kg immediately after transfer, but this density doubled in 8 wk. More internally developing insects were collected by the elevator buckets when the clean grain flowed over the infested grain compared with the externally developing insects. β-Cyfluthrin application as a residual insecticide reduced the insect densities in the elevator boot, which consequently reduced the insect transfer to clean grain. Cleaning the bucket elevator boot area and applying residual insecticide monthly should minimize clean grain contamination.