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 ofIridomyrmex humilis, and that the true trail pheromone may be multicomponent. Trail-following responses ofI. humilis workers to several concentrations of syntheticZ9-16∶ALD, a constituent of the Pavan's gland, were found to be comparable to responses to gaster extract trails containing ca. 100 times lessZ9-16∶ALD. Of the five aldehyde analogs tested, only (Z)-7-hexadecenal (Z7-16∶ALD) elicited significant trail-following. However, following responses to severalZ9-16∶ALD-Z7-16∶ALD combinations were lower than responses toZ9-16∶ALD alone. Trails on filter paper of biologically relevant concentrations ofZ9-16∶ALD lose activity within 2 hr in the laboratory. The release rate ofZ9-16∶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.