Trail-following responses of the Argentine ant, Iridomyrmex humilis (Mayr), to a synthetic trail pheromone component and analogs

Behavioral evidence indicates that (Z)-9-hexadecenal (Z9-16:ALD) is a trail pheromone component of Iridomyrmex humilis, and that the true trail pheromone may be multicomponent. Trail-following responses of I. humilis workers to several concentrations of synthetic Z9-16:ALD, a constituent of the Pavan's gland, were found to be comparable to responses to gaster extract trails containing ca. 100 times less Z9-16:ALD. Of the five aldehyde analogs tested, only (Z)-7-hexadecenal (Z7-16:ALD) elicited significant trail-following. However, following responses to several Z9-16:ALD-Z7-16:ALD combinations were lower than responses to Z9-16:ALD alone. Trails on filter paper of biologically relevant concentrations of Z9-16:ALD lose activity within 2 hr in the laboratory. The release rate of Z9-16:ALD measured from filter paper trails was 0.25 ± 0.10 pg/cm-sec. This was used to estimate the trail-following threshold for this compound of Argentine ant workers.