PITFALL TRAPS AND GRAIN SAMPLES AS INDICATORS OF INSECTS IN FARM-STORED WHEAT

Pitfall traps and grain samples taken with a vacuum probe provided data on insect infestation in farm-stored wheat in 26 Kansas counties. Insects were monitored at 65-d intervals from July 1986 through March 1987. Early detection when populations were low in July and March was accomplished best by pitfall traps. The traps detected insects in 61.5% of the bins of wheat within 1 mo of harvest. In September and November, > 95% of the bins were infested. More than half the bins contained Rhyzopertha dominica (F.), an especially damaging pest of Kansas farm-stored grain. Absence of insects in either traps or grain samples could not be interpreted as proof that grain was insect-free. Each method was a more efficient detector of infestations than the other in certain seasons and for certain insects. The center of the grain mass contained a significantly greater percentage of the total number of insects in grain samples from September to January and a significantly greater percentage of the trapped insects from July to March than other positions. Correlation coefficients relating the number of all insects in traps to the number in grain samples taken directly below the traps did not exceed 0.65 until March. In September and November, when insect populations were greatest, 25 insects were captured in traps for each insect in grain samples. In January, the ratio decreased to 9:1.