|Subramanyam, B - KANSAS STATE UNIV|
Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 10, 2004
Publication Date: August 31, 2004
Citation: Flinn, P.W., Subramanyam, B., Arthur, F.H. 2004. Comparison of aeration and spinosad for suppressing insects in stored wheat. Journal of Economic Entomology. V.97(4):1465-1473. Interpretive Summary: Insects reduce the quality of stored grain and other stored products in the U.S. and in the world. It is estimated that losses due to insects are 5 to 10%, or about 1.25 to 2.5 billion dollars. Field studies were conducted in Kansas to compare the effectiveness of controlled aeration and a new biological insecticide, spinosad, to control insects in bins of stored wheat. No live red flour beetles or rusty grain beetles and only very low numbers of lesser grain borers were found in wheat treated with spinosad during the 6-month storage period. Aeration also controlled the insects well, but not as well as spinosad. The number of rusty grain beetles and red flour beetles in aerated bins was not greater than 2 live insects per kg of wheat during the 6-months. However, in the untreated bins insect numbers were as high as 70 adults per kg in January 2003. This study demonstrated that spinosad was very effective in controlling the primary insect pests of stored wheat. Controlled aeration was also effective in suppressing these insects, but not as effective as the spinosad treatment. This is the first field study comparing the effectiveness of spinosad and aeration in managing insects in stored grain. Information from this study will be of great interest to farmers and elevator managers, especially those interested in organic grain storage methods.
Technical Abstract: Field studies were conducted during July 2002 to January 2003 for evaluating the effects of controlled aeration and a commercial biological insecticide, spinosad, in suppressing insect populations in stored wheat. Six cylindrical steel bins were filled with newly harvested (2002 crop year) hard red winter wheat on 9 and 10 July 2002. Each bin contained 30.7 metric tons (1,100 bushels) of wheat. Wheat in two bins was left untreated (control), whereas wheat in two bins was treated with spinosad, and in another two bins was subjected to aeration using aeration controllers. Spinosad was applied to wheat at the time of bin filling to obtain a rate of 1 mg (AI)/kg. Aeration controllers were set to run the fans when ambient air temperature fell below 23.9ºC, 18.3ºC, and 7.2ºC for the first, second, and third cooling cycles, respectively. We added 400 adults each of the rusty grain beetle, Cryptolestes ferrugineus (Stephens), lesser grain borer, Rhyzopertha dominica (F.), and red flour beetle, Tribolium castaneum (Herbst), to the grain at monthly intervals between July and October 2002. Insect density in the bins was estimated monthly by taking 3-kg grain samples from 21 locations within each bin using a pneumatic grain sampler. No live T. castaneum or C. ferrugineus and very low densities of R. dominica (<0.008 adults/kg) were found in wheat treated with spinosad during the 6-month sampling period. Density of C. ferrugineus and T. castaneum in aerated bins did not exceed 2 adults/kg (the Federal Grain Inspection Service standard for infested wheat), whereas that of R. dominica was 12 adults/kg in November 2002; which subsequently decreased to 3 adults/kg in January 2003. In the untreated (control) bins, R. dominica density increased faster than that of C. ferrugineus or T. castaneum. Density of R. dominica peaked at 58 adults/kg in October 2002 and decreased subsequently, whereas T. castaneum density was 10 adults/kg in October 2002 but increased to 78 adults/kg in January 2003. Density of C. ferrugineus increased steadily during the 6-mo study period and was highest (6 adults/kg) in January 2003. This is the first report comparing the field efficacy of spinosad and aeration in managing insects in farm bins. Our results suggest that spinosad is effective in suppressing R. dominica, C. ferrugineus, and T. castaneum populations in stored wheat.