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.

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 half of the grain mass, from the discharge spout at the base of the bins, and from residue remaining in empty bins before 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 with 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 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 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 approximately 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 with samples from the grain masses. Cleaning the empty bins before refilling with newly-harvested wheat resulted in a significantly-reduced density of pest insects in discharge spouts later, and the effect lasted at least 12 wk after filling.

Immigration of insects into bins storing newly harvested wheat on 12 Kansas farms.

Adult insects entering 34 bins (36-238 t capacity) storing newly harvested hard red winter wheat on 12 farms in Kansas were sampled from July through December 1998 using ventilation traps. Insects moving through the grain stored in these bins were sampled using probe traps. During the fourth week of storage, probe traps captured Cryptolestes ferrugineus in all bins, Ahasverus advena in 32 bins, Typhaea stercorea in 31 bins, and Rhyzopertha dominica in 13 bins. Means+/-SE of 5.6+/-0.7 C. ferrugineus, 0.5+/-0.2 R. dominica, 3.5+/-0.3 A. advena, and 3.5+/-0.7T. stercorea were caught per day in probe traps. Ventilation traps provided a more direct measure than probe traps of the total numbers of insects entering bins storing newly harvested wheat. Immigration of A. advena and T. stercorea increased more than that of other species during the storage period, exceeding that of C. ferrugineus and R. dominica during some weeks. Rhyzopertha dominica had the lowest immigration rate. Bin size did not influence ventilation trap catch but as many as a third more insects may immigrate into large bins at the eaves compared with small bins because of their larger circumference. The mean numbers of C. ferrugineus, R. dominica, A. advena and T. stercorea captured in ventilation traps at the bin cap were 7.8, 2.7, 15.1 and 18.3 times, respectively, those captured in ventilation traps at the bin eaves. The estimated means+/-SE for total numbers of insects entering a bin each day were 13.6+/-4.2 C. ferrugineus, 6.3+/-4.7 R. dominica, 5.8+/-1.4 A. advena, and 21.9+/-8.2T. stercorea. Estimates of immigration rates can improve the accuracy with which insect densities are predicted using insect population growth models, and allow computer models to be used more effectively in managing insect pests. Insect infestations may be reduced by screening the openings between the bin cap and the roof, or the roof and the side walls.

Mate-seeking behavior and reduced mating byEphestia cautella (Walker) in a sex pheromone-permeated atmosphere.

The mating rate ofEphestia cautella (Walker) was inversely related to the level of pheromone permeating the air. However, permeation did not prevent mating by altering the number of females calling or the frequency, duration, or pattern of male flight. Instead, permeation probably prevented mating by reducing the distance from which a male can respond to a female. The pheromone level necessary to achieve a particular reduction in mating increases with moth density.