Suppression of Beetles in Stored Wheat by Augmentative Releases of Parasitic Wasps

Abstract

Field studies were conducted to assess the effectiveness of the parasitoid wasps, Cephalonomia waterstoni (Gahan), and Choetospila elegans (Westwood), for controlling Cryptolestes ferrugineus (Stephens), rusty grain beetle and Rhyzopertha dominica (F.), lesser grain borer. On 6 July 1993 and 7 July 1994, adults of both C. ferrugineus and R. dominica were released at monthly intervals into 6 steel grain bins each containing 27.2 t of hard red winter wheat, Triticum aestivum L. Adults of both parasitoid species were released into 3 of the bins 21 d after the 1st beetle release. The amount of suppression of C.ferrugineus by C. waterstoni could not be measured in either year of this study because C. waterstoni infested the control bins. However, C. elegans was effective in suppressing R. dominica populations. In 1993 and 1994, R. dominica populations were suppressed by 98 and 91% compared with the control bins. After 198 d from initial beetle release in 1993, the treatment bins averaged 0.05 R. dominica per kilogram and the control bins averaged 2.06 R. dominica per kilogram. After 131 d from initial beetle release in 1994, the treatment bins averaged 6.94 R. dominica per kilogram and the control bins averaged 81.03 R. dominica per kilogram.