Do aphids infected with entomopathogenic fungi continue to produce and respond to alarm pheromone?

The response of pea aphids, Acyrthosiphon pisum, to aphid alarm pheromone was not modified by infection with Beauveria bassiana. Approximately 50% of uninfected and infected aphids responded to synthetic alarm pheromone. The simulated attack of aphids infected with B. bassiana did not elicit a response in uninfected aphids. Preliminary air entrainment experiments of both uninfected aphids and aphids at different stages of B. bassiana (generalist pathogen) or P. neoaphidis (obligate pathogen of aphids) demonstrated that B. bassiana infected aphids produced less alarm pheromone than uninfected aphids and, conversely, P. neoaphidis infected aphids produced more alarm pheromone than uninfected aphids. These results are discussed with particular emphasis on the different life history strategies of these two pathogens. We hypothesise that the obligate, specialist pathogen, P. neoaphidis, is under greater selection pressure to increase pathogen transmission and survival resulting in modified host behaviour, than the generalist pathogen, B. bassiana.