Comparison of three trap types for monitoring insect populations in stored grains.

Three trap types--probe, cone, and sticky--were used to monitor insect populations infesting shelled maize, Zea mays L., housed in galvanized steel storage bins. Sticky traps were suspended in the headspace 1 m above the grain mass, probe traps were inserted into the grain near the top and bottom of the grain mass, and cone traps were positioned at the surface of the grain mass. Although there was some overlap, each trap type was rather specific in the range of insect species trapped. Probe traps positioned near the grain surface trapped mostly Oryzaephilus surinamensis (L.), Tribolium castaneum (Herbst), and Cynaeus angustus (LeConte); whereas those positioned near the bottom of the grain mass trapped mostly Sitophilus zeamais Motschulsky. Cone traps caught mostly Typhaea stercorea (L.), Cryptolestes spp., and Ahasverus advena Waltl. Sticky traps caught primarily stored-product moths [Plodia interpunctella (Hübner) and Sitotroga cerealella (Olivier)] and A. advena. In addition to catching pest species, cone traps also caught hemipteran predators and hymenopteran parasitoids, and sticky traps caught large numbers of parasitoids. Although probe traps caught smaller numbers of several pest species than cone traps, these traps generally detected the presence of these species at the same time as cone traps, in addition to trapping other species that were not detected at all in cone traps. Therefore, a combination of sticky traps in the grain bin headspace and probe traps positioned just below the grain surface is probably most efficient for monitoring the presence of pest and beneficial insect species in grain storage. If pests cannot be eliminated from the space beneath the false floor of a grain bin, probe traps set at the bottom of the grain mass should provide the best early warning of infestation by species colonizing a grain mass by this route.