Fight and flee : caste decisions during an invasion

Abstract

Sociality is a trade-off between personal reproduction and investment in helping others to survive and reproduce. Seven species of Australian gall-inducing thrips have a helping caste (soldiers). A kleptoparasite in the genus Koptothrips that invades and destroys thrips colonies is hypothesized to have evolutionarily shaped this caste. The two investigations presented here both center on one potential evolutionary reaction to the threat of invasion; the production of an alarm pheromone. In the first study, reproductives and soldiers were assessed in the presence or absence of a putative alarm pheromone. Reproductives moved more directly and quickly than soldiers in the trials, but no impact of the pheromone was detected. In the second study, soldier willingness to fight was assessed in relation to this chemical (or blend). Again, no change in behaviour was detected in the trials. Taken together, these two investigations suggest that chemical communication may not have arisen within the gall inducing thrips.