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

The sex pheromone composition of alfalfa plant bugs, Adelphocoris lineolatus (Goeze, 1778), from Central Europe was investigated to test the hypothesis that insect species across a wide geographical area can vary in their pheromone
composition. Potential interactions between the pheromone and a known attractant,(E)-cinnamaldehyde, were also assessed. Coupled gas chromatography-electroantennography (GC-EAG) using male A. lineolatus antennae and volatile extracts collected from females, which had been shown to attract males in earlier field experiments, revealed the presence of three physiologically active compounds, which were identified by coupled GC-mass spectrometry (GC-MS) and GC peak enhancement as hexyl butyrate, (E)-2-hexenyl butyrate and (E)-4-oxo-2-hexenal. A ternary blend of these compounds in 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-hexenalfrom the ternary blend or substitution of (E)-4-oxo-2-hexenal by (E)-2-hexenal resulted in loss of activity. These results indicate that the studied Central European population is similar in its pheromone composition to that of a previously reported East Asian population. Interestingly, another EAG-active compound, 1-hexanol, was also present
in extracts of females. When tested in combination with the ternary pheromone blend, 1-hexanol significantly reduced male catches. This antagonism produced a dose response effect with relatively small doses showing remarkable influence, which suggests that 1-hexanol may act as a sex pheromone antagonist for A. lineolatus. Furthermore, when field tested in combination with the sex pheromone, (E)-cinnamaldehyde did not increase male catches significantly; however, the combination attracted both males and females. Prospects for practical applications are discussed.