Location: Pest Management and Biocontrol ResearchTitle: Sex pheromone component ratios and mating isolation among three lygus plant-bug species of North America Author
Submitted to: Naturwissenschaften
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/20/2013
Publication Date: 11/15/2013
Citation: Byers, J.A., Fefer, D., Levi-Zada, A. 2013. Sex pheromone component ratios and mating isolation among three lygus plant-bug species of North America. Naturwissenschaften. 12:1115-1123. Interpretive Summary: Three species of plant bug, the western tarnished plant bug, the tarnished plant bug, and the pale legume bug are major pests of many agricultural crops in North America. Previous studies have shown males and females contain relatively large amounts of three volatile chemicals that are emitted as a defense against predators. We found that female tarnished plant bugs and pale legume bugs emit a ratio of these chemicals that is much different from the ratio emitted by female western tarnished plant bugs. The different ratios of chemicals emitted by females of these species suggest the chemicals may be used to attract mates (act as a sex pheromone). Both sexes of western tarnished plant bug contain nearly equal amounts of these major volatiles, but females emit more than males. When these chemicals were tested in traps in the field, only males of the three species were captured. Furthermore, all three chemicals in the proper ratios were essential for males of the three species to distinguish females of their own species from those of the other two species. Our study suggests that males and females of all three species use these volatile chemicals for defense, but females also use them as a sex pheromone. Identification of these sex pheromones may lead to development of attractive traps for detecting or monitoring plant bug populations.
Technical Abstract: Three species of Lygus (Hemiptera: Miridae), L. hesperus, L. lineolaris, and L. elisus are major pests of many agricultural crops in North America. Previous studies have shown males and females contain µg amounts of (E)-4-oxo-2-hexenal, hexyl butyrate, and (E)-2-hexenyl butyrate, and the volatiles are emitted as a defense against predators. We used gas chromatography - mass spectrometry to quantify the three major volatiles and found that female L. lineolaris and L. elisus have a 4:10 ratio of hexyl butyrate to (E)-2-hexenyl butyrate that is reversed from the 10:1 ratio in female L. hesperus (males of the three species have about a 10:1 ratio). These reversed ratios among females of the species suggest a sex pheromone role. Because both sexes of L. hesperus have nearly equal amounts of the major volatiles, females should release more to attract males. This expectation was supported because individual females of L. hesperus released 86 ng/h of hexyl butyrate during the night (18:00-7:00) compared to only 8 ng/h or less from males. We used a slow-rotating pair of traps releasing various blends of the major butyrate ester of each species at 3 µg/h (the minor butyrate released proportionally) and (E)-4-oxo-2-hexenal at about 2 µg/h. Using a subtractive method to detect synergism, the catches of only Lygus males suggest that (E)-4-oxo-2-hexenal is essential for all three species, while (E)-2-hexenyl butyrate is essential for L. elisus and L. lineolaris, and hexyl butyrate is essential for L. hesperus. However, all three components are used by each species since ratios of the butyrate esters are critical for conspecific attraction and heterospecific avoidance by males, and thus play a role in reproductive isolation among the three species. Because L. hesperus males and females are known to emit these major volatiles for repelling ant predators, our study links defensive allomones in Lygus bugs with an additional use as sex pheromones.