Aphid alarm pheromone produced by transgenic plants affects aphid and parasitoid behavior

Abstract

The alarm pheromone for many species of aphids, which causes dispersion in response to attack by predators or parasitoids, consists of the sesquiterpene (E)-beta-farnesene (Ebetaf). We used high levels of expression in Arabidopsis thaliana plants of an Ebetaf synthase gene cloned from Mentha x piperita to cause emission of pure Ebetaf. These plants elicited potent effects on behavior of the aphid Myzus persicae (alarm and repellent responses) and its parasitoid Diaeretiella rapae (an arrestant response). Here, we report the transformation of a plant to produce an insect pheromone and demonstrate that the resulting emission affects behavioral responses at two trophic levels.

Fig. 1.

Sesquiterpene region of the gas chromatograms (HP-1 column, flame ionization detector) of the volatile chemicals collected from flowering A. thaliana (Col-0) wild-type (A) and the transgenic line FS11-4 (B). β-Caryophyllene (peak 1) is the main constituent of the headspace of the wild-type plant, whereas Eβf (peak 2) is the major component of the transgenic plant volatiles, which also contain a greatly reduced amount of β-caryophyllene. (C) Coupled GC–electroantennography using antennae from a female aphid parasitoid, D. rapae. The effluent from the GC column was split and directed simultaneously to the GC detector and the antennal preparation. The upper trace is the GC of air entrainment volatiles from transgenic line FS9-2; the lower trace shows the electroantennograph response (marked by an arrow) to the major peak, Eβf.

Fig. 2.

Alarm response of colonies of M. persicae to volatiles released by A. thaliana (Col-0). The percentage of aphids moving after 1 min and 15 min was recorded, and the arcsin-transformed data were subjected to ANOVA. Columns with different letters indicate responses that are significantly different (P < 0.05; n = 10). (A) Response to 1-μl droplets of air entrainment samples of transgenic and wild-type A. thaliana volatiles, compared with the response to synthetic Eβf in hexane and a hexane control. (B) Response to 20-ml samples of vapor from the headspace above individual plants of transgenic and wild-type A. thaliana, enclosed in 2-liter vessels, and synthetic Eβf.

Fig. 3.

Responses of M. persicae to an attractive visual cue (a yellow bead) placed in the treated arm of a four-arm olfactometer, in combination with volatiles from wild-type and transgenic A. thaliana FS11-4. Time spent (A) and number of entries (B) into treated and control arms are compared. Mean values (n = 6) are shown; bars indicate ± SE. The yellow bead was significantly attractive to aphids when presented together with wild-type volatiles (P = 0.021 for time spent; P = 0.034 for number of entries; paired t test). However, with volatiles from the transgenic A. thaliana line FS11-4, the yellow bead was no longer attractive.

Fig. 4.

Time spent by foraging D. rapae on wild-type and transgenic A. thaliana plants. Parasitoids were released at the center of the plants, and individual behaviors were scored by using the observer software. Mean values (n = 10) are shown; bars indicate ± SE. The total amount of time spent foraging was significantly higher on the transgenic A. thaliana line FS9-2 (P = 0.026, unpaired t test).