Orientation and Locomotion of Apterous Aphids Dislodged from Their Hosts by Alarm Pheromone

The aphids, Acyrthosiphon pisum (Harris), Hyadaphis erysimi (Kaltenbach) and Macrosiphum euphorbiae (Thomas), displayed 2 types of behavior after being dislodged from their hosts. Aphids mechanically dislodged from a settled colony initially exhibited thanatosis; then 73-97% oriented to, and walked towards, a vertical dowel which they climbed. In contrast, when mechanically dislodged from an unsettled colony or dislodged by alarm pheromone from a settled colony, aphids moved immediately, walked faster and farther with less change in direction, and only 7-20% oriented towards a vertical dowel. When H. erysimi and Myzus persicae (Sulzer) were dislodged by alarm pheromone within 15 cm of a turnip plant in a greenhouse plot, 59 and 50%, respectively were recovered from this plant while the remainder were located on 8 peripheral turnips. When mechanically dislodged, 80% of H. erysimi and 75% of M. persicae were recovered from the central turnip. This study demonstrates that aphids dislodged by alarm pheromone disperse by increasing their rate of locomotion and decreasing their orientation to vertical images.