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Title: WHEAT IN BINS AND DISCHARGE SPOUTS, AND GRAIN RESIDUES ON FLOORS OF EMPTY BINS IN CONCRETE GRAIN ELEVATORS AS HABITATS FOR STORED-GRAIN BEETLES AND THEIR NATURAL ENEMIES

Author
item REED, CARL - KANSAS STATE UNIV
item HAGSTRUM, DAVID - 5430-05-30 RETIRED
item Flinn, Paul
item ALLEN, R - KANSAS STATE UNIV

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/27/2002
Publication Date: 7/1/2003
Citation: REED, C.R., HAGSTRUM, D.W., FLINN, P.W., ALLEN, R.F. WHEAT IN BINS AND DISCHARGE SPOUTS, AND GRAIN RESIDUES ON FLOORS OF EMPTY BINS IN CONCRETE GRAIN ELEVATORS AS HABITATS FOR STORED-GRAIN BEETLES AND THEIR NATURAL ENEMIES. JOURNAL OF ECONOMIC ENTOMOLOGY 96(3): 996-1004. 2003.

Interpretive Summary: Insects are major pests of grain in the U.S., and their presence affects quality of grain in domestic and export markets. Insect populations in wheat residues in empty bins at grain elevators were studied to determine if these residues were a major reason why grain in storage bins becomes infested. We also investigated the effect of bin cleaning on the insect density measured several months later in grain residues in the discharge spout. The rusty grain beetle dominated the insect populations in all types of samples. The rusty grain beetle was an early colonizer, and was found in the grain mass shortly after new grain was added. The lesser grain borer appeared to be slower to colonize grain and grain residue, but sometimes developed large populations between July and December. Weevils often were present in the grain mass, and were often abundant in the discharge spouts. Weevils were also abundant in grain residue in empty bins in May and June. Grain in discharge spouts usually had high numbers of insects, and minute parasitic wasps (natural enemies of the beetles). The population of natural enemies appeared to increase when the density of pest insects increased after a lag of about one month, and decreased when the population of pest insects decreased. Grain in discharge spouts appeared to provide an incubation chamber for pest insects, and removing this grain periodically should reduce the resident populations. Grain residue in empty bins was often densely infested compared to samples from the grain mass. Cleaning the empty bins before re-filling with newly-harvested wheat resulted in a great reduction of insect pests in discharge spouts several months later. The results of this study are important to the grain handling industry because it shows that cleaning bins and removing grain residues from discharge spouts reduces the resident population of insects that can infest new grain and thus, reduce the need to use fumigants.

Technical Abstract: Wheat stored in upright concrete bins at seven grain elevators in central Kansas was sampled intermittently for insects over a 2.5-yr period by collecting samples from the upper one-half of the grain mass, from the discharge spout at the base of the bins, and from residue remaining in empty bins prior to the 2000 wheat harvest. Samples were taken from the grain mass with a power vacuum sampler (PV) and from the discharge spouts (DS) by dropping grain onto the reclaim belt beneath the bins. The density and species distribution in the residue samples were compared to those found in the DS samples and samples from the grain mass (PV). Cryptolestes spp. dominated the insect populations in all types of samples, constituting >40 % of all insects in the PV samples in three of five time periods and >60 % of all insects in DS samples in four of the five time periods. Cryptolestes spp. was an early colonizer, being found in the grain mass shortly after new grain was added. Rhyzopertha dominica appeared to be slower to colonize grain and grain residue, but sometimes developed large populations (i.e., 2.4 ± 0.7 adults/kg between July and December of 2000). Sitophilus spp. weevils often were present in grain masses, were often abundant in grain in the discharge spouts (i.e., 11.1 ± 2.9 adults/kg between July and December of 2000), and were abundant in grain residue in empty bins in May/June 2000 (5.3 ± 0.7 adults/kg). Differences in density and species distribution of insects in grain in the upper part of the grain mass and those in the discharge spouts indicated that the populations were not closely related. Grain in discharge spouts usually was densely infested, and parasitic wasps, natural enemies of several of the beetles, were found when the density of the pest insects was greater than about 10/kg. The population of natural enemies appeared to increase when the density of pest insects increased after a lag of about one month, and decreased when the population of pest insects decreased. Grain in discharge spouts appeared to provide an incubation chamber for pest insects, and removing this grain periodically should reduce the resident populations. Residue in empty bins often was densely infested compared to samples from the grain masses. Cleaning the empty bins before re-filling with newly-harvested wheat resulted in a significantly-reduced density of pest insects in discharge spouts later, and the effect lasted at least 12 weeks after filling.