Phytophagous insects have evolved traits that help them avoid predation risks, traits that may be affected by characteristics of the host plant. Since most phytophagous insects have narrow host ranges, we expect differences in risk avoidance between plant-specialized populations of several closely related insect lineages. To test this hypothesis, we used the pea aphid (Acyrthosiphon pisum), which forms a complex of about 15 biotypes, each adapted to one or a few species of legume plants (Fabaceae). We examined the differences in defensive behaviors of 38 clones from 13 distinct plant-specialized biotypes of pea aphids. We exposed mature aphids to simulated breath of a mammalian herbivore, a cue that causes part of the aphids in a colony to immediately drop off the plant to avoid incidental ingestion during mammal feeding. Dropping tendency varied substantially between biotypes (15–93% average rates). Dropping rates of a certain biotype of aphid reflected their host's palatability to mammalian herbivores, with ∼80–90% rates in fodder and pasture plants and ∼15–40% dropping in inedible plants. The dropping tendency showed no correlation with walking ability (tarsal & body length), nor with the tendency to escape in response to the alarm pheromone released by conspecifics in response to arthropod enemies. The specialization on a specific host plant brings with it particular selective pressures, and it seems that the palatability of the plants to mammals promotes behavioral divergence between biotypes, reinforcing diversification through ecological divergence.
Bibliographical noteFunding Information:
The authors would like to thank Jean Peccoud for early discussion on this project and fruitful feedbacks on dropping variation in pea aphid biotypes, and Rami Reshef from the university of Haifa for the use of his lab's microscope. This work was supported by the Agence Nationale de la Recherche (grant ANR-11-BSV7-007 to JCS) and by The Israel Science Foundation (grant No. 248/17 to MI).
© 2018 Gesellschaft für Ökologie
- Dropping response
- Host biotypes
- Incidental ingestion
- Mammalian herbivores
- Plant edibility
ASJC Scopus subject areas
- Ecology, Evolution, Behavior and Systematics