In most aphid species, the volatile sesquiterpene (E)-β-farnesene (Eβf) is released as an alarm pheromone in response to predation and is also emitted continuously at low levels. Some aphid predators use Eβf as a foraging cue, suggesting that the benefits to aphids of signaling via Eβf must be weighed against the cost of increasing apparency to natural enemies.
At the same time, aphid alarm pheromone has been shown to mediate mutualistic interactions between ants and aphids, in which ants protect “myrmecophilic” aphids while collecting aphid honeydew (a rich source of carbohydrates). Nault et al. (1976) observed that ants became very aggressive in the presence of alarm pheromone and increased their rate of attack on aphid predators, but did not attack aphids. In contrast, when alarm pheromone was applied to colonies of aphid species that are not ant-tended (non-myrmecophilic), ants became aggressive towards the aphids themselves (Nault et al., 1976). More recently, ants’ ability to perceive Eβf was confirmed by Mondor and Addicott (2007).
It was frequently believed that ant-aphid mutualisms were tightly linked, coevolved responses. However, it has been proposed that these dyads may evolve, especially in facultative as opposed to obligate mutualists, as ‘loose relationships’ between species explaining why ants are capable of tending multiple aphid species, either simultaneously or sequentially, in their native habitats. The Argentine ant, for example, is capable of tending many different aphid species in its native environment and many of these aphids are likely to use E-b-farnesene as their alarm pheromone. Interestingly invasive ants, such as Argentine ant in Europe and USA, may form mutualistic associations with native aphids due to selection for this trait in the ant’s native environment.
The study of aphid-ant interaction will be therefore very useful non only to better understand the interaction between these taxa, but also to improve our knowledge about ant invasive species.
(Photo of Alison Bockoven from the blog 6legs2many).
References
- Mondor, E., Addicott, J. (2006) Do exaptations facilitate mutualistic associations between invasive and native species? Biological Invasions, 9 (6), 623-628 DOI: 10.1007/s10530-006-9062-0
- Vandermoten S, Mescher MC, Francis F, Haubruge E, Verheggen FJ (2012) Aphid alarm pheromone: an overview of current knowledge on biosynthesis and functions. Insect Biochemistry and Molecular Biology, 42, 155-63 PMID: 22178597.
- Verheggen, F., Haubruge, E., De Moraes, C., Mescher, M. (2009) Social environment influences aphid production of alarm pheromone Behavioral Ecology, 20, 283-288 DOI: 10.1093/beheco/arp009
