Worker behavioral response to lignoceric and hexacosanoic acid, two major components of the solider defensive secretion in formosan subterranean termites (Blattodea: Rhinotermitidae)

Termites are eusocial insects that live in organized colonies consisting of reproductives, workers, and soldiers. The soldier caste is morphologically specialized for colony defense, and some species produce a soldier-specific defensive secretion. The Formosan subterranean termite, Coptotermes formosanus Shiraki, maintains a higher proportion of soldiers (~10%) than the native subterranean termites in Reticulitermes (< 2%), and the soldier defensive secretion makes up over a third of a C. formosanus soldier’s body weight. Many components of the C. formosanus defensive secretion have been identified, and some of the major components include lignoceric acid (LA) and hexacosanoic acid (HA). Previous studies have shown that soldier defensive secretions can act as repellants for workers and attractants for soldiers (Nasutitermes spp.), but the behavioral influence has not been explored in C. formosanus. Using a choice assay, we analyzed choice behavior and food consumption of groups of 20 workers exposed to LA, HA, a mix of LA and HA, the crude extract of the defensive secretion, and a control over 168 hours. We found that workers avoided filter paper treated with LA, HA, and the crude extract at some time points, and they avoided the mix of LA and HA at every time point. Workers also consumed significantly less filter paper treated with the LA and HA mix. The results imply that C. formosanus soldier defensive secretion may contain avoidant cues for workers, alerting them of dangerous situations, and that LA and HA may be two of the primary compounds responsible for this behavioral response.