Article

Emission of Alarm Pheromone in Aphids: a Non-Contagious Phenomenon

Department of Functional and Evolutionary Entomology, Gembloux Agricultural University, Passage des Déportés 2, Gembloux, Belgium.
Journal of Chemical Ecology (Impact Factor: 2.75). 10/2008; 34(9):1146-8. DOI: 10.1007/s10886-008-9528-x
Source: PubMed

ABSTRACT

In response to attack by natural enemies, most aphid species release an alarm pheromone that causes nearby conspecifics to cease feeding and disperse. The primary component of the alarm pheromone of most species studied is (E)-beta-farnesene. We recently demonstrated that the production and accumulation of (E)-beta-farnesene during development by juvenile aphids is stimulated by exposure to odor cues, most likely by (E)-beta-farnesene emitted by other colony members. Here, we tested whether the release of (E)-beta-farnesene can be triggered by exposure to the alarm pheromone of other individuals, thereby amplifying the signal. Such contagious emission might be adaptive under some conditions because the amount of (E)-beta-farnesene released by a single aphid may not be sufficient to alert an appropriate number of individuals of the colony to the presence of a potential threat. By using a push-pull headspace collection system, we quantified (E)-beta-farnesene released from Acyrthosiphon pisum aphids exposed to conspecific alarm signals. Typical avoidance behavior was observed following exposure to (E)-beta-farnesene (i.e., aphids ceased feeding and dropped from host-plant); however, no increase in alarm pheromone amount was detected, suggesting that contagious release of (E)-beta-farnesene does not occur.

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    • "When other aphids detect this cue, they remove their stylets from the host plant and fall, jump, or walk away to escape potential danger (Edwards et al., 1973; Montgomery and Nault, 1977; Roitberg and Myers, 1978; Wohlers, 1981; Braendle and Weisser, 2001). Aphids that sense alarm pheromone do not appear to release additional pheromone (Hatano et al., 2008; Verheggen et al., 2008b). Alarm pheromones are emitted by nearly all aphid species, and the sesquiterpene E-b-farnesene (Ebf), the most common component, has been found in more than 40 aphid species (Xiangyu et al., 2002). "
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    • "However, Kunert et al. (2005) reported that A. pisum react more strongly to the frequency of pheromone releases than to the amount of pheromone released during each signaling event. This observation is consistent with the results of two later studies, which found that aphids do not propagate or amplify the alarm signal by emitting additional EBF in response to perception of the alarm pheromone (Hatano et al., 2008a; Verheggen et al., 2008b). Thus, the frequency, rather than the intensity of alarm pheromone emission events, may determine the scale of the response induced. "
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