Oleic acid emitted from frozen Trogoderma spp. larvae causes conspecific behavioral aversion

Authors: DOMINGUE, MICHAEL - Animal And Plant Health Inspection Service (APHIS); Morrison, William - Rob; Yeater, Kathleen; MYERS, SCOTT - Animal And Plant Health Inspection Service (APHIS)

Submitted to: Chemoecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/12/2020
Publication Date: 4/1/2020
Citation: Domingue, M.J., Morrison III, W.R., Yeater, K.M., Myers, S.W. 2020. Oleic acid emitted from frozen Trogoderma spp. larvae causes conspecific behavioral aversion. Chemoecology. 30:161-172. https://doi.org/10.1007/s00049-020-00307-3.
DOI: https://doi.org/10.1007/s00049-020-00307-3

Interpretive Summary: The khapra beetle (KB) often gathers in clusters on non-food sources before they are adults. This grouping behavior presents a problem for detection in biosurveillance and exclusion because larvae may remain undetected away from food sources. In this study, we examined whether we could extract compounds that would affect larval movement of khapra beetle or other closely related species of Dermestid larvae such as warehouse beetle (WB) and larger cabinet beetle (LCB). Extracts of specimens from all three species had hydrocarbon profiles similar to previous reports for KB. However, extracts often had 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 or much greater amounts compared to solvent controls. When oleic acid content of the extract was high, there was always repulsion of the larvae toward the other side of the arena. At low concentrations, extracts with oleic acid were not attractive or repellant for KB and LCB, but became attractive for WB. We also performed the assay using a large range of doses of neat oleic acid for KB only. At the lowest dose (1 µg), oleic acid was mildly attractive, but became strongly repellant at higher doses beginning at 100 µg. The repellency observed in this study suggests the possibility for management applications. Further research is needed to fully determine the biological basis for this behavior and whether it exists for different life stages, or is affected by physiological status.

Technical Abstract: Khapra beetle (KB), Trogoderma granarium, larvae often enter diapause and are observed assembled in clusters on non-food sources. This behavioral process presents a problem for detection in bio surveillance because larvae can remain cryptic. Here, we examine whether extractable compounds from larvae affect movement of conspecific or heterospecific, but related larvae, namely, the warehouse beetle (WB), Trogoderma variabile, and larger cabinet beetle (LCB), Trogoderma inclusum. Hexane extracts of specimens from all three species had hydrocarbon profiles similar to previous reports for KB. However, extracts often had 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) or much greater amounts (68-131 µg) to hexane controls. When oleic acid content of the extract was high, there was always repulsion of the larvae toward the other side of the arena. At low concentrations, extracts with oleic acid were not attractive or repellant for KB and LCB, but became attractive for WB. We also performed the assay using a large range of doses of neat oleic acid for KB only. At the lowest dose (1 µg), oleic acid was mildly attractive, but became strongly repellant at higher doses beginning at 100 µg. The repellency observed in this study suggests the possibility for 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.