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Pyrazines Attract Catocheilus Thynnine Wasps.

Bohman B, Peakall R - Insects (2014)

Bottom Line: Additionally, the semiochemical 3-(3-methylbutyl)-2,5-dimethylpyrazine, a close analogue to 2-(3-methylbutyl)-3,5,6-trimethylpyrazine, identified in five other species of thynnine wasps, was equally active.Our findings suggest the possibility that despite the high specificity normally characterising sex pheromone systems, the evolution of sexual deception may not be entirely constrained by the need to precisely match the sex pheromone constituents and blends.Such evolutionary flexibility may be particularly important during the early stages of speciation.

View Article: PubMed Central - PubMed

Affiliation: Research School of Chemistry, The Australian National University, Canberra ACT 0200, Australia. bjorn.bohman@anu.edu.au.

ABSTRACT
Five previously identified semiochemicals from the sexually deceptive Western Australian hammer orchid Drakaea livida, all showing electrophysiological activity in gas chromatography-electroantennogram detection (EAD) studies, were tested in field bioassays as attractants for a Catocheilus thynnine wasp. Two of these compounds, (3,5,6-trimethylpyrazin-2-yl)methyl 3-methylbutanoate and 2-(3-methylbutyl)-3,5,6-trimethylpyrazine, were attractive to male wasps. Additionally, the semiochemical 3-(3-methylbutyl)-2,5-dimethylpyrazine, a close analogue to 2-(3-methylbutyl)-3,5,6-trimethylpyrazine, identified in five other species of thynnine wasps, was equally active. The three remaining compounds from D. livida, which were EAD-active against Catocheilus, did not attract the insects in field trials. It is interesting that two structurally similar compounds induce similar behaviours in field experiments, yet only one of these compounds is present in the orchid flower. Our findings suggest the possibility that despite the high specificity normally characterising sex pheromone systems, the evolution of sexual deception may not be entirely constrained by the need to precisely match the sex pheromone constituents and blends. Such evolutionary flexibility may be particularly important during the early stages of speciation.

No MeSH data available.


Responses of male Catocheilus wasps to bioassays presenting choices of compounds 1, 5 and 6 in different combinations and at different concentrations. The wasp responses are shown as proportions of the total, further partitioned into approach (black) versus combined land and attempted copulation (grey). The number of wasps responding to each treatment and the outcomes of G-tests for the  hypothesis of no difference between the two choices, based on the total number of responses, are also shown. (A) Compounds 1versus5 with 5 at 3-fold higher concentration. (B) Compounds 1versus5 with 1 at 3-fold higher concentration. (C) Compound 5versus a blend of 5 and 1 at a 3:1 ratio. (D) Compound 5versus6 at equal 1-fold concentration (1×). (E) Compound 5versus6 at equal 3-fold higher concentration (3×). (F) Compound 6versus a blend of 5 and 1 at a 3:1 ratio. For experiments A, C, D and F, proportions are shown as means ±se, each calculated across two replicate experiments. For the 1× concentration 3 µL of a 10 μg/μL solution of the compound or blend was applied to the bead and allowed to evaporate before use.
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insects-05-00474-f002: Responses of male Catocheilus wasps to bioassays presenting choices of compounds 1, 5 and 6 in different combinations and at different concentrations. The wasp responses are shown as proportions of the total, further partitioned into approach (black) versus combined land and attempted copulation (grey). The number of wasps responding to each treatment and the outcomes of G-tests for the hypothesis of no difference between the two choices, based on the total number of responses, are also shown. (A) Compounds 1versus5 with 5 at 3-fold higher concentration. (B) Compounds 1versus5 with 1 at 3-fold higher concentration. (C) Compound 5versus a blend of 5 and 1 at a 3:1 ratio. (D) Compound 5versus6 at equal 1-fold concentration (1×). (E) Compound 5versus6 at equal 3-fold higher concentration (3×). (F) Compound 6versus a blend of 5 and 1 at a 3:1 ratio. For experiments A, C, D and F, proportions are shown as means ±se, each calculated across two replicate experiments. For the 1× concentration 3 µL of a 10 μg/μL solution of the compound or blend was applied to the bead and allowed to evaporate before use.

Mentions: It was not feasible to test all possible combinations or concentrations of the semiochemicals. However, informed by the results from the closely related system D. glyptodon/Z. trilobatus [15], and by preliminary trials, we proceeded to implement a set of paired choice experiments for specific combinations and ratios that had been indicated to be attractive (See Figure 2). Each experiment commenced with preparation of the dummies that were loaded with 1–9 μL of different synthetic compounds/combinations based on working solutions of either 1 μg/µL or 10 µg/µL (see results for details). Note that the amount of compound applied (1 to a max of 30 µg) may at first seem to be high, given that the Drakaea flowers/female wasps produce such minute amounts of the compounds. However, only at these levels on the dummy can rates and intensity of male wasp attraction be achieved at the dummies that closely match those at orchid flowers (see [15]). Also, at these levels, pollinator responses to the bead can be maintained over the 1–2 h required for each experiment. Although not used for more than 2 h in formal experiments, dummies remain attractive for more than 24 h, indicating that the semiochemicals are released from the beads at very low levels, in a similar way to how they are released from flowers. A single experiment consisted of four to six trials of three min duration, with two choices presented simultaneously (>0.5 m apart, perpendicular to wind direction). Trials were abandoned if there was no response. The four main experiments were replicated twice, where possible on different days. Between trials, dummies were stored in a sealed container. G–tests applying William’s correction comparing the proportion of responses between the two choices for a given experiment were performed in GenAlEx 6.5 [20,21].


Pyrazines Attract Catocheilus Thynnine Wasps.

Bohman B, Peakall R - Insects (2014)

Responses of male Catocheilus wasps to bioassays presenting choices of compounds 1, 5 and 6 in different combinations and at different concentrations. The wasp responses are shown as proportions of the total, further partitioned into approach (black) versus combined land and attempted copulation (grey). The number of wasps responding to each treatment and the outcomes of G-tests for the  hypothesis of no difference between the two choices, based on the total number of responses, are also shown. (A) Compounds 1versus5 with 5 at 3-fold higher concentration. (B) Compounds 1versus5 with 1 at 3-fold higher concentration. (C) Compound 5versus a blend of 5 and 1 at a 3:1 ratio. (D) Compound 5versus6 at equal 1-fold concentration (1×). (E) Compound 5versus6 at equal 3-fold higher concentration (3×). (F) Compound 6versus a blend of 5 and 1 at a 3:1 ratio. For experiments A, C, D and F, proportions are shown as means ±se, each calculated across two replicate experiments. For the 1× concentration 3 µL of a 10 μg/μL solution of the compound or blend was applied to the bead and allowed to evaporate before use.
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Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4592595&req=5

insects-05-00474-f002: Responses of male Catocheilus wasps to bioassays presenting choices of compounds 1, 5 and 6 in different combinations and at different concentrations. The wasp responses are shown as proportions of the total, further partitioned into approach (black) versus combined land and attempted copulation (grey). The number of wasps responding to each treatment and the outcomes of G-tests for the hypothesis of no difference between the two choices, based on the total number of responses, are also shown. (A) Compounds 1versus5 with 5 at 3-fold higher concentration. (B) Compounds 1versus5 with 1 at 3-fold higher concentration. (C) Compound 5versus a blend of 5 and 1 at a 3:1 ratio. (D) Compound 5versus6 at equal 1-fold concentration (1×). (E) Compound 5versus6 at equal 3-fold higher concentration (3×). (F) Compound 6versus a blend of 5 and 1 at a 3:1 ratio. For experiments A, C, D and F, proportions are shown as means ±se, each calculated across two replicate experiments. For the 1× concentration 3 µL of a 10 μg/μL solution of the compound or blend was applied to the bead and allowed to evaporate before use.
Mentions: It was not feasible to test all possible combinations or concentrations of the semiochemicals. However, informed by the results from the closely related system D. glyptodon/Z. trilobatus [15], and by preliminary trials, we proceeded to implement a set of paired choice experiments for specific combinations and ratios that had been indicated to be attractive (See Figure 2). Each experiment commenced with preparation of the dummies that were loaded with 1–9 μL of different synthetic compounds/combinations based on working solutions of either 1 μg/µL or 10 µg/µL (see results for details). Note that the amount of compound applied (1 to a max of 30 µg) may at first seem to be high, given that the Drakaea flowers/female wasps produce such minute amounts of the compounds. However, only at these levels on the dummy can rates and intensity of male wasp attraction be achieved at the dummies that closely match those at orchid flowers (see [15]). Also, at these levels, pollinator responses to the bead can be maintained over the 1–2 h required for each experiment. Although not used for more than 2 h in formal experiments, dummies remain attractive for more than 24 h, indicating that the semiochemicals are released from the beads at very low levels, in a similar way to how they are released from flowers. A single experiment consisted of four to six trials of three min duration, with two choices presented simultaneously (>0.5 m apart, perpendicular to wind direction). Trials were abandoned if there was no response. The four main experiments were replicated twice, where possible on different days. Between trials, dummies were stored in a sealed container. G–tests applying William’s correction comparing the proportion of responses between the two choices for a given experiment were performed in GenAlEx 6.5 [20,21].

Bottom Line: Additionally, the semiochemical 3-(3-methylbutyl)-2,5-dimethylpyrazine, a close analogue to 2-(3-methylbutyl)-3,5,6-trimethylpyrazine, identified in five other species of thynnine wasps, was equally active.Our findings suggest the possibility that despite the high specificity normally characterising sex pheromone systems, the evolution of sexual deception may not be entirely constrained by the need to precisely match the sex pheromone constituents and blends.Such evolutionary flexibility may be particularly important during the early stages of speciation.

View Article: PubMed Central - PubMed

Affiliation: Research School of Chemistry, The Australian National University, Canberra ACT 0200, Australia. bjorn.bohman@anu.edu.au.

ABSTRACT
Five previously identified semiochemicals from the sexually deceptive Western Australian hammer orchid Drakaea livida, all showing electrophysiological activity in gas chromatography-electroantennogram detection (EAD) studies, were tested in field bioassays as attractants for a Catocheilus thynnine wasp. Two of these compounds, (3,5,6-trimethylpyrazin-2-yl)methyl 3-methylbutanoate and 2-(3-methylbutyl)-3,5,6-trimethylpyrazine, were attractive to male wasps. Additionally, the semiochemical 3-(3-methylbutyl)-2,5-dimethylpyrazine, a close analogue to 2-(3-methylbutyl)-3,5,6-trimethylpyrazine, identified in five other species of thynnine wasps, was equally active. The three remaining compounds from D. livida, which were EAD-active against Catocheilus, did not attract the insects in field trials. It is interesting that two structurally similar compounds induce similar behaviours in field experiments, yet only one of these compounds is present in the orchid flower. Our findings suggest the possibility that despite the high specificity normally characterising sex pheromone systems, the evolution of sexual deception may not be entirely constrained by the need to precisely match the sex pheromone constituents and blends. Such evolutionary flexibility may be particularly important during the early stages of speciation.

No MeSH data available.