Studies on the dispersal behaviour of apterous pea aphids acyrthosiphon pisum (Harris)
Creators: name: Roitberg, Bernard D.
Publisher: name: University of British Columbia
Year: 2010

description: The dispersal behaviour of apterous pea aphids, Acyrthosipon pi sum (Harris) was studied in the laboratory and field. In the laboratory, aphids exhibited two types of behaviour while on the ground, after dropping from plants in response to predators. Most aphids showed a high frequency of turning and tended to return to the plant they left, while a smaller proportion walked in straight lines and did not return to the plant they left. Adults and older nymphs had the highest proportion of individuals which showed the second type of behaviour and adults showed the greatest tendency to disperse to plants more distant than the nearest available plants. Young instar aphids were less successful at locating a host than older nymphs and adults. Aphids were placed on the central bean seedlings within plots, inside large field cages. Adult coccinellids were released into two of the cages while the other cage remained predator-free. Aphids in the cages with predators frequently moved between plants, while aphids in the predator-free cage did not. Adult aphids colonized more plants and had a lower mortality while on the ground than all other instars. Aphids did not show a preferred dispersal direction and the distance dispersed by aphid nymphs was proportional to the density of aphids on the plant they left. The importance of emigrating apterae in the exploitation of new resources and the regulation of aphid populations is discussed. Bean plants infected with an aphid transmitted virus were transplanted into the central position of bean plots in the field cages. Aphids were placed on the central infected plants and adult coccinellids were released into two of the three cages for three days. Aphids frequently moved to other plants from the centre infected plant in the two cages with predators but not in the predator-free cage. When plants were examined two weeks later, significantly more plants were infected with virus in the cages with predators than in the predator-free cage. New virus infections were correlated with plants that were visited or colonized by aphids from the central infected plant. The influence of predators in the spread of aphid transmitted diseases is discussed. In laboratory experiments, pea aphids from Vancouver were presented with alarm pheromone from irritated conspecifics. Adult and fourth instar aphids responded to the pheromone by either dropping, running or backing up. Instars one, two and three responded to the pheromone only when a vibratory stimulus accompanied it. A high proportion of all instars responded to the double stimulus by dropping. When adult aphids from Vancouver and Kamloops were presented with alarm pheromone, the Kamloops adults exhibited a more conservative reaction to alarm pheromone. Kamloops adults also were more conservative about leaving their plant when confronted by a coccinellid predator. A hypothesis is presented, which accounts for the differences in escape reactions between instars and biotypes. The hypothesis takes into consideration predation risk, escape behaviour repertoire and survival on the ground. Pea aphid adults resisted heat paralysis longer than first instars when subjected to high temperature treatments. All aphids succumbed to paralysis sooner at 42°C than at 37.5°C, but there appeared to be no difference in aphid survival in dry compared to moist conditions at high temperatures. Kamloops aphids were not more resistant to high temperatures.