Electrophysiological Responses of Eighteen Species of Insects to Fire Ant Alarm Pheromone

Abstract

Olfaction plays a dominant role in insect communication. Alarm pheromones, which alert other insects of the same species of impending danger, are a major class of releaser pheromones. The major components of alarm pheromones in red imported fire ants, honeybees and aphids have been identified as 2-ethyl-3,6-dimethylpyrazine (2E-3,6-DP), isopentyl acetate (IPA), and E-β-farnesene (EβF), respectively. In this study, electroantennography (EAG) responses to EDP (a mixture of 2-ethyl-3,6-dimethylpyrazine and 2-ethyl-3,5-dimethylpyrazine), IPA and EβF were investigated in a wide range of insect species. Beside imported fire ants, the EDP (2-ethyl-3,6(5)-dimethylpyrazine) elicited significant EAG response from all other tested insects, including six ant species and one hybrid ant, honeybee, bagrada bug, lady beetle, housefly, small hive beetle, yellow fever mosquito, termite, bedbug, water hyacinth weevil, southern green stink bug and two aphid species. In contrast, IPA elicited significant EAG response only in the honeybee, red imported fire ant, an Aphaenogaster ant, and the water hyacinth weevil. The EβF only elicited EAG responses in two aphids, small hive beetle and housefly. The results clearly indicate that EDP can be detected by widespread insect species that did not coevolve with S. invicta and further suggested alkylpyrazine may activate multiple generally tuned olfactory receptors (ORs) across a wide number of insect species.

Keywords: Alarm pheromone; EAG; GC-EAD; Solenopsis invicta; semiochemical.

Figure 1

GC-EAD responses of S. invicta workers, female and male alates to the alarm pheromone 2-ethyl-3,6-dimethylpyrazine (2E-3,6,-DP) and its isomer 2-ethyl-3,5-dimethylpyrazine (2E-3,5,-DP). (A) Chemical structures of 2E-3,5,-DP and 2E-3,6,-DP. (B) EAD responses of female alates (1, 5), male alates (2) and workers (3, 4) and FID chromatogram (6) (peak a: 2E-3,6-DP and peak b: 2E-3,5-DP).

Figure 2

Fire ant alarm pheromone, EDP, elicited concentration-dependent EAG response in S. invicta workers (A), female alates (B) and male alates (C). Dose-response curves (D) for workers, male and female alates. Each point represents the mean (±SEM) of six to ten tested antennae (D).

Figure 3

The representative EAG traces elicited by 100 μg/μL EDP, EβF and IPA in S. invicta (A), hybrid fire ant (S. invicta x S. richteri) (B), black imported fire ant (S. richteri) (C), pharaoh ant (M. pharaonis) (D), little black ant (M. minimum) (E), aphenogaster ant (A. picea)(F), and tawny crazy ant (N. fulva) (G) The histogram (H) shows the EAG responses in different ants species (mean ± SEM). Means sharing no letter on the top of bars are significantly different, as determined by one-way analysis of variance with Tukey’s test, and significant values were set at p < 0.05. The ANOVA was performed for each individual species response to the odorants and the differing letters only have meaning within a species, not between all species.

Figure 4

The representative EAG traces elicited by 100 μg/μL EDP, EβF and IPA dilution in honeybee (A. mellifera) (A), small hive beetle (A.tumida) (B), begrada bug (B. hilaris) (C), nine-spotted lady beetle (C. novemnotata) (D), eastern subterranean termite (R. flavipes) (E), southern green stink bug (N. viridula) (F), water hyacinth weevil (N. eichhorniae) (G), bed bug (C. lectularius) (H), yellow fever mosquito (A. aegypti) (I), housefly (M. domestica) (J), bird cherry oat aphid (R. padi) (K) and oleander aphid (A. merii) (L). M. the histogram (M) shows the EAG responses (mean ± SEM) in all 12 insect species. The sample for each insect species consisted of 6–12 antennae. Means sharing no letter on the top of bars are significantly different, as determined by one-way ANOVA with Tukey’s test, and significant values were set at p < 0.05. The ANOVA was performed for each individual species response to the odorants and the differing letters only have meaning within a species, not between all species.