Real-time analysis of alarm pheromone emission by the pea aphid (acyrthosiphon pisum) under predation

Abstract

Upon attack by predators or parasitoids, aphids emit volatile chemical alarm signals that warn other aphids of a potential risk of predation. Release rate of the major constituent of the alarm pheromone in pea aphids (Acyrthosiphon pisum), (E)-b-farnesene (EBF), was measured for all nymphal and the adult stage as aphids were attacked individually by lacewing (Chrysoperla carnae) larvae. Volatilization of EBF from aphids under attack was quantified continuously for 60 min at 2-min intervals with a rapid gas chromatography technique (zNose) to monitor headspace emissions. After an initial burst, EBF volatilization declined exponentially, and detectable amounts were still present after 30 min in most cases. Total emission of EBF averaged 16.33 +/- 1.54 ng and ranged from 1.18 to 48.85 ng. Emission was higher in nymphs as compared to adults. No differences between pea aphid life stages were detected for their speed of alarm signal emission in response to lacewing larvae attack. This is the first time that alarm pheromone emission from single aphids has been reported.

Fig. 1

Air entrainment setup showing 4 ml vial with inserted ZNose™ sampling needle and air inlet needle

Fig. 2

Typical time course of (E)-ß-farnesene emission in the experiment. This example is from a first instar aphid (L1) attacked by a lacewing larva

Fig. 3

Sum of (E)-ß-farnesene in nanogram ± SE emitted over the entire 60-min collection period for immature instars (L1–L4) and adults. Significant differences in (E)-ß-farnesene production between instars are indicated by different letters; P ≤ 0.05, Kruskal–Wallis test, N = 10

Fig. 4

Peak emission of (E)-ß-farnesene in nanogram ± SE per 2 min sampling interval. Significant differences in (E)-ß-farnesene emission between instars are indicated by different letters; P ≤ 0.05, Kruskal–Wallis test, N = 10

Fig. 5

Lag time between initial attack by lacewing larvae and peak emission of (E)-ß-farnesene in minutes ± SE. There was no statistical difference in lag time among instars; P > 0.05, Kruskal–Wallis test, N = 10