Sex Pheromone of the Alfalfa Plant Bug, Adelphocoris lineolatus: Pheromone Composition and Antagonistic Effect of 1-Hexanol (Hemiptera: Miridae)

Abstract

The sex pheromone composition of alfalfa plant bugs, Adelphocoris lineolatus (Goeze), from Central Europe was investigated to test the hypothesis that insect species across a wide geographical area can vary in pheromone composition. Potential interactions between the pheromone and a known attractant, (E)-cinnamaldehyde, were also assessed. Coupled gas chromatography-electroantennography (GC-EAG) using male antennae and volatile extracts collected from females, previously shown to attract males in field experiments, revealed the presence of three physiologically active compounds. These were identified by coupled GC/mass spectrometry (GC/MS) and peak enhancement as hexyl butyrate, (E)-2-hexenyl butyrate and (E)-4-oxo-2-hexenal. A ternary blend of these compounds in a 5.4:9.0:1.0 ratio attracted male A. lineolatus in field trials in Hungary. Omission of either (E)-2-hexenyl-butyrate or (E)-4-oxo-2-hexenal from the ternary blend or substitution of (E)-4-oxo-2-hexenal by (E)-2-hexenal resulted in loss of activity. These results indicate that this Central European population is similar in pheromone composition to that previously reported for an East Asian population. Interestingly, another EAG-active compound, 1-hexanol, was also present in female extract. When 1-hexanol was tested in combination with the ternary pheromone blend, male catches were reduced. This compound showed a dose-response effect with small doses showing a strong behavioral effect, suggesting that 1-hexanol may act as a sex pheromone antagonist in A. lineolatus. Furthermore, when (E)-cinnamaldehyde was field tested in combination with the sex pheromone, there was no increase in male catch, but the combination attracted both males and females. Prospects for practical application are discussed.

Keywords: Adelphocoris lineolatus; Electroantennography; Field attraction; Miridae; Sex pheromone.

Fig. 1

Catches of Adelphocoris lineolatus males in traps baited with live virgin A. lineolatus males on green bean pods, live virgin A. lineolatus females on green bean pods, green bean pods alone or unbaited. Treatments marked with the same letter are not different (Kruskal-Wallis test, pairwise comparison by Wilcoxon test with Benjamini-Hochberg correction at p = 0.05) ∑ = total number of A. lineolatus males caught in the experiment (box plot diagram indicating median, minimum, maximum, the 1st and 3rd quartiles of catches of the respective treatments)

Fig. 2

Coupled gas chromatography-electroantennogram (GC-EAG) analysis of a female Adelphocorus lineolatus headspace extract, with bioactive peaks labeled. The extract used for GC-EAG shows a ratio of pheromone constituents different from that from air entrainment samples, which were used for quantitative analysis. FID = flame ionization detector

Fig. 3

Catches of Adelphocoris lineolatus males in traps baited with ternary and binary combinations of hexyl butyrate, (E)-2-hexenyl butyrate and (E)-4-oxo-2-hexenal and unbaited. Treatments marked with the same letter are not different (Kruskal-Wallis test, pairwise comparison by Wilcoxon test with Benjamini-Hochberg correction at p = 0.05) ∑ = total number of A. lineolatus males caught in the experiment (box plot diagram indicating median, minimum, maximum, the 1st and 3rd quartiles of catches of the respective treatments)

Fig. 4

Catches of Adelphocoris lineolatus males in traps baited with a ternary pheromone blend, with addition of 1-hexanol, and unbaited. The 1-hexanol was added either in the same or a separate dispenser. Treatments marked with the same letter are not different (Kruskal-Wallis test, pairwise comparison by Wilcoxon test with Benjamini-Hochberg correction at p = 0.05) ∑ = total number of A. lineolatus males caught in the experiment (box plot diagram indicating median, minimum, maximum, the 1st and 3rd quartiles of catches of the respective treatments)

Fig. 5

Catches of Adelphocoris lineolatus males and females in traps baited with a ternary pheromone blend, (E)-cinnamaldehyde, their combination and unbaited. Treatments marked with the same letter are not different (Kruskal-Wallis test, pairwise comparison by Wilcoxon test with Benjamini-Hochberg correction at p = 0.05) ∑ = total number of A. lineolatus males/females caught in the experiment (box plot diagram indicating median, minimum, maximum, the 1st and 3rd quartiles of catches of the respective treatments)

Fig. 6

Catches of Adelphocoris lineolatus males in traps baited with a ternary pheromone blend with a standard dose of (E)-4-oxo-2-hexenal, with a 5-fold increased dose of (E)-4-oxo-2-hexenal, with (E)-2-hexenal substituted for (E)-4-oxo-2-hexenal and unbaited. Treatments marked with the same letter are not different (Kruskal-Wallis test, pairwise comparison by Wilcoxon test with Benjamini-Hochberg correction at p = 0.05) ∑ = total number of A. lineolatus males caught in the experiment (box plot diagram indicating median, minimum, maximum, the 1st and 3rd quartiles of catches of the respective treatments)