Newswise — On August 1st, a joint team of researchers from the University of Amsterdam (UvA) and North Carolina State University made a significant discovery. They successfully pinpointed the precise combination of pheromone chemicals employed by male moths during their courtship rituals. This breakthrough sheds light on the intricate chemical blend utilized by both male and female moths within this moth group for essential short-range communication. The results of their study were published in the esteemed scientific journal Current Biology.
In the world of moths, scent compounds play a crucial role in the intricate dance of courtship. Male moths rely on these scents to attract and entice female moths of the same species for mating. The process is particularly challenging as both partners must navigate the darkness to find and identify each other. Female moths secrete sex pheromones that aid in this identification process. Once the male locates a potential mate, it becomes his responsibility to impress and convince the female that he is a suitable partner. This delicate interplay of scents and behaviors forms the basis of their mating rituals.
Aphrodisiac from plants
The study reveals that male Chloridea virescens moths use a special ingredient for their love potion, which they get from plants. When they munch on these plants, the plants release a signal called "methyl salicylate." This signal serves two purposes: to heal the plant and to call for help when the plant is under attack from enemies. Surprisingly, male moths can use this substance in their own perfume mix. They can do this either when they were caterpillars and ate the plants or when they are adults and drink nectar from the plants.
Astrid Groot, a researcher at the University of Amsterdam's Institute for Biodiversity and Ecosystem Dynamics (IBED), expresses the novelty of the finding. According to her, it's a fresh revelation that the courtship pheromone of these moths includes substances obtained from plants. Previously, it was believed that these moths and their relatives created their sex pheromones from scratch without any external sources.
The reason behind this phenomenon is not entirely clear, but it seems that when a male moth consumes this substance from plants, it somehow signals to the female that he can handle the plant's defense substance or that he is a skilled forager as an adult. In either case, eating this substance enhances the male moths' chances of successfully mating.
According to Groot, the discovery of methyl salicylate in the pheromone cocktails of male moths was unexpected. She suggests that this sexual signal might have evolved in males because females could already detect and respond to the substance.
Specific receptors in females
Almost 35 years ago, scientists initially identified the composition of the sex pheromone of male moths. In the present day, with advancements in chemical analysis techniques, they employed gas chromatography to study the male pheromone with higher sensitivity. This led them to uncover some new chemical compounds that were previously unknown, such as methyl salicylate. The significance of methyl salicylate was further explored through laboratory experiments.
The researchers used a technique to measure changes in electropotential charge on the antennae of female moths. Through this method, they observed that even though methyl salicylate was barely detectable in gas chromatography studies, it elicited a significant response in females. This is because female moth antennae possess two smell receptors that are specifically tuned to recognize methyl salicylate, enabling them to identify this chemical in the mixture released by male moths.
The researchers conducted an experiment where they decreased the amount of methyl salicylate produced by male moths. As a result, the mating success of these males decreased. However, when the males were given methyl salicylate, their mating success returned to normal, indicating the aphrodisiac-like nature of this chemical.
Storage in the hair pencils
Furthermore, the researchers compared wild moths with specimens from the laboratory. They found that male moths captured in soybean fields in North Carolina had substantial amounts of methyl salicylate in their hair pencils, which are the male organs responsible for secreting the pheromone mixture.
In the laboratory, the researchers decreased the levels of methyl salicylate in moths that were fed an artificial diet. However, when the male lab moths were given methyl salicylate through nectar-like sugar water, they stored it in their hair pencils. When these males were encouraged to court females, the methyl salicylate vanished from their hair pencils once again, as they incorporated it into their pheromone mixture.
Publication details
Yang Liu, Jeremy J. Heath, Sai Zhang, Michiel van Wijk*, Guirong Wang, Jan Buellesbach, Ayako Wada-Katsumata, Astrid T. Groot* and Coby Schal, A mosaic of endogenous and plant-derived courtship signals in moths, Current Biology, 1 August 2023, doi: 10.1016/j.cub.2023.07.010, * Affiliated to the University of Amsterdam
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