Predator-induced morphological shift in the pea aphid

Aphids exhibit a polymorphism whereby individual aphids are either winged o r unwinged. The winged dispersal morph is mainly responsible for the coloni zation of new plants and, in many species, is produced in response to adver se environmental conditions. Aphids are attacked by a wide range of special ized predators and predation has been shown to strongly influence the growt h and persistence of aphid colonies. In two experiments, we reared two clon es of pea aphid (Acyrthosiphon pisum) in the presence and absence of predat ory ladybirds (Coccinella septempunctata or Adalia bipunctata). In both exp eriments, the presence of a predator enhanced the proportion of winged morp hs among the offspring produced by the aphids. The aphid clones differed in their reaction to the presence of a ladybird, suggesting the presence of g enetic variation for this trait. A treatment that simulated disturbance cau sed by predators did not enhance winged offspring production. The experimen ts indicate that aphids respond to the presence of a predator by producing the dispersal morph which can escape by flight to colonize other plants. In contrast to previous examples of predator-induced defence this shift in pr ey morphology does not lead to better protection against predator attack, b ut enables aphids to leave plants when mortality risks are high.