PREDICTING INSECT DENSITY FROM PROBE TRAP CATCH IN FARM-STORED WHEAT

Insect populations infesting wheat stored in four bins on two Kansas f arms were monitored from early July 1996 through to the middle of Janu ary 1997, Estimates of adult insect density based upon the numbers of adult insects caught using probe traps differed from those based upon the number of insects found in grain samples. These differences were a result of differences in numbers of insects found and percentages of traps or grain samples with insects. Traps detected insects 15 to 37 d earlier than grain samples, The depth of traps below the grain surfac e tended to influence both the total number and species composition of the insects that were caught. Traps inserted with the top just below the grain surface collected an average of 1.9 times more Cryptolestes ferrugineus (Stephens), 1.2 times more Rhyzopertha dominica (F.), 4.1 times more Ahasverus advena (Waltl) and 77.4 times more Typhaea sterdo minica (L.) than traps inserted with the top 7.6 cm below the grain su rface, However, trap depth did not have a significant effect on the nu mber of R, dominica caught and on only 12 to 21% of sampling dates did trap depth have a significant effect on the number of insects of othe r species that were caught, Grain temperatures in three of the bins av eraged 30 degrees C during the first 70 d of storage and then decrease d by 0.2 degrees C/d. Grain in the other bin was initially more than 1 0 degrees C warmer and grain temperature decreased by 0.2 degrees C/d over the full storage period. The numbers of insects captured in traps decreased as grain temperature decreased even though grain samples in dicated that insect populations were still growing, Thus, trap catches did not estimate insect population density consistently throughout th e storage period, A method was developed in the current paper to adjus t for the effect of seasonal changes in temperature on trap catch. Pub lished by Elsevier Science Ltd.