Even- and odd-numbered fatty acids used as worker arrestant aggregation pheromone components in the Formosan subterranean termite Coptotermes formosanus

Pheromones play a pivotal role in coordinating collective activities. Recent research has demonstrated that workers of the Japanese subterranean termite, Reticulitermes speratus, secrete an aggregation pheromone that induces quick assemble and prolonged stay at the pheromone source for nestmate workers, facilitating efficient dead-wood digestion and colony expansion. The question remains: do other termite species also utilize aggregation pheromones? In this study, we report that workers of the Formosan subterranean termite, Coptotermes formosanus, use a mixture of fatty acids as part of the pheromone components to maintain worker aggregation for extended periods of time. Through bioassays and gas-chromatography mass-spectrometry (GC–MS) analysis, we determined that a mixture of four fatty acids including palmitoleic acid, palmitic acid, (Z)-10-heptadecenoic acid, and stearic acid possesses arrestant activity but little or no attractant activity. Also, the inclusion of cholesterol and cuticular hydrocarbons reinforces only its arrestant activity. Further, GC–MS analysis of extracts of wood and soil, which serve as termite food, indicated that the pheromone components other than palmitic acid are not derived from their food, and GC analysis of extracts from different parts of the worker’s body revealed that these components were most likely produced in the midgut and excreted to the outside of the body via the hindgut. These findings suggest that the aggregation pheromone components and their functions in C. formosanus are largely different from those in R. speratus. This research provides insights into the differences among termite species in the development of chemical signals triggering aggregation behavior.