Behavioral effects of naturally extracted fatty acid on Trogoderma larvae

Abstract: Khapra beetle (KB), Trogoderma granarium, larvae have a prolonged diapause and can remain viable clustering on non-food sources for months. This existence of such cryptic larvae presents a problem for management as they can evade detection in small numbers, while having the potential to quickly infest products when the proper conditions arise.We extracted compounds from larvae that might potentially affect KB, and the larvae of two related species, the warehouse beetle (WB), Trogoderma variable, and larger cabinet beetle (LCB), Trogoderma inclusum. Hexane extracts of all three species contained cuticular hydrocarbon profiles similar to those known for KB. All extracts also tended to have high amounts of oleic acid, which increased if specimens were frozen before extraction. Behavioral assays were performed by comparing extracts that provided low oleic acid doses (< 2 μg) versus much greater amounts (~100μg) to hexane controls. When oleic acid content of the extract was high, there was always repulsion of the larvae of all three species toward the other side of the arenas. At low oleic acid doses, extracts were not attractive or repellent for KB and LCB, but were attractive for WB. We also tested a large range of doses of only oleic acid, for KB larvae only. At the lowest doses we provided (1 μg), oleic acid was not attractive, but it became significantly repellent at higher doses beginning at 100 μg. The repellence observed in this study suggests potential management applications.Further research is needed to fully comprehend the biological basis for this behavior and whether it exists for different life stages or is affected by physiological status.