Augmentative releases of parasitoid wasps in stored wheat reduces insect fragments in flour

Field studies were conducted to assess the effectiveness of the parasitoid wasp, Theocolax elegans, for reducing insect fragments in flour by suppressing populations of Rhyzopertha dominica in six bins, each containing 27 tonnes of wheat. Beetles were released into all the six bins at monthly intervals for 3 months. Parasitoid wasps were released into three of the bins, 21 days after the first beetle release. Wheat samples from the bins were milled to determine the effects of parasitoid releases on insect fragment counts in flour. In the first year of the study, after 198 days of storage, insect fragment counts were 9.4 and 31 per 50 g flour in the treatment and control bins. However, because of high variability, the means were not significantly different. New grain was used in the second year of the study, and higher numbers of beetles were released. After 131 days of storage, fragment counts averaged 56 and 487/50 g in the treatment and control bins, a reduction in the former of 89%. In the second year of the study, insect myosin in the treatment and control bins averaged 0.27 and 3.23 ng/well, a percentage reduction in the treated bin of 92%. The number of insect damaged kernels (IDK) was significantly lower in the treatment than in the control bins in both years of the study. In the first year, IDK was 6 and 15 IDK/100 g wheat in the treatment and control bins respectively, a reduction in the former of 61%. In the second year, IDK was 12 and 148 IDK/100 g wheat, in the treatment and control bins respectively, a reduction of 92%. This study showed that augmentative releases of parasitoid wasps into bins of stored wheat reduced damage to wheat kernels and the number of insect fragments in flour.