Uptake, retention, and repellency of a potential carrier of active ingredients in crack and crevice treatments for stored-grain beetles

Crack and crevice treatments are important in modern stored-beetle management, because: (1) pests are abundant in such microhabitats, (2) they potentially deliver insecticides to insect pests without contaminating food products, and (3) they can significantly reduce the need for broadcast spray applications and/or fumigations. As part of on-going research into the development of novel insecticide delivery systems to be used in processed and unprocessed food environments, we examined uptake and behavioural responses of Oryzaephilus surinamensis to an electrostatically chargeable powder, EntostatTM. Entostat is a processed plant wax and has been identified as a potential carrier for active ingredients to be delivered to cracks and crevices in food facilities. Depending upon the initial Entostat concentration in rolled oats, 0.03-0.26 μg powder was extracted from individual beetles 72 h after being transferred from treated to untreated food. SEM images showed that Entostat adhered to all body parts, including joints, between body segments, and at the insertions of body hairs. Choice experiments showed that O. surinamensis individuals were repelled, when rolled oats in cracks contained >5% Entostat. In a three-choice experiment cracks contained: (1) untreated oats, (2) oats mixed with 5% (w/w) Entostat, or (3) oats mixed with 5% (w/w) Entostat and a piece of filter paper containing a beetle attractant which was also inserted into the crack. The beetle attractant did not significantly increase the attractiveness of the crack in which it was applied, but the average powder uptake of beetles from cracks treated with the attractant was significantly higher than from the other cracks. Results presented here suggested that Entostat adhering to insects was retained over several days and that considerable amounts of Entostat were taken up even when beetles were offered a choice between treated and untreated cracks.