Effects of fungal infection on the alarm response of pea aphids

Pea aphids (Acyrthosiphon pisum, Homoptera: Aphididae) infected with the fungal pathogen Erynia neoaphidis (Zygomycetes: Entomophthorales) were less sensitive to the aphid alarm pheromone (E)-beta-farnesene than uninfected aphids. Approximately 83% of the healthy aphids and 45% of the infected aphids (2 and 3 days post-inoculation) responded to the alarm pheromone. The percentage of nonresponding aphids increased as the disease progressed. When squeezed (simulated attack) healthy aphids and aphids at an advanced stage of infection elicited a response similar to that of uninfected aphids, suggesting that the alarm pheromone was produced by diseased insects. Aphids infected for 2 or 3 days did not recolonize the upper regions of bean plants after dislodgment. This showed that infected aphids are less active at late stages of infection. The implications of these results are discussed with respect to fungal transmission and biological control. Copyright 1999 Academic Press.