Male moths use an aphrodisiac during mating to feel "macho"

A team of researchers led by North Carolina State University has recently identified the specific blend of pheromones used by male moths during courtship as they attempt to attract females. 

These findings – including a newly discovered ‘aphrodisiac’- shed new light on the complex blend of chemicals used in basic short-range communication between male and female moths.

“Macho” moths

The newly found aphrodisiac is a chemical derived from plants called methyl salicylate. When attacked by herbivores, plants emit this chemical both as a healing mechanism and a “cry for help” to the natural enemies of these herbivores. 

According to the scientists, its use in a pheromone blend by male Chloridea virescens moths could be considered as a “macho” display showing that the male was capable of defeating both the plant’s defense mechanisms and its call to the moth’s enemies, thus making the moth a more worthy mating option.

“These close-range interactions provide valuable insight into both species recognition – how females recognize males of the same species – and female choice in mate selection,” said senior author Coby Schal, a professor of Entomology at NC State. “This interaction gives females some insight into a particular male’s history.”

Focus of the study

The family of moths the experts studied includes a variety of generalist species feeding on over 350 plant species across the Americas, such as the corn earworm, the tobacco budworm, and the fall armyworm – all of which are considered major pests in South Carolina. 

Female moths of these species initiate the mating process by emitting pheromones over longer-range distances. Males respond to these “calls” by flying closer to the females and emitting their own unique blend of pheromones, which are then assessed by females in order to chose whether to mate or not.

By using gas chromatography – a method in which chemical compounds are separated in a controllable oven – to identify the chemicals contained in the male pheromone blend. 

What the researchers learned 

Although methyl salicylate was barely detectable in the gas chromatography studies, a close investigation of the antennae of female moths revealed two olfactory receptors that are tuned to this compound, and help females easily recognize it in the blend emitted by males.

To assess this chemical’s importance in mating processes, the researchers artificially reduced its amount emitted by males, and discovered that their mating success decreased, an aspect proving methyl salicylate’s aphrodisiac-like quality.

Clever strategy

While only tiny amounts of this compound were found in moths which were fed artificial diets in the lab, male moths captured from North Carolina soybean fields had large amounts of methyl salicylate in their hairpencils (the male organs emitting the pheromone blend). 

By adding larger amounts of the chemical into the lab moth’s diets through a nectar-like sugar water drink, the scientists discovered that the moths easily incorporated the chemical and sequestered it in their hairpencils. When prompted to court females, those hairpencils exhibited lower amounts of methyl salicylate, suggesting that males used most of it in their pheromone cocktail.

“It was surprising to find methyl salicylate in male moth pheromone blends, but the evidence from this paper suggests that male moths take up and sequester methyl salicylate as larvae while chewing up plants or as adults by drinking flower nectar. Males may have evolved sexual signals that match the sensory bias exhibited by females in responding to methyl salicylate,” Schal concluded.

The study is published in the journal Current Biology.

More about moth mating rituals

Moth mating rituals can vary quite a bit depending on the species, but there are some common themes. Most moths use a combination of visual, chemical, and sometimes auditory signals to attract and find mates.

The process usually begins when the female moth releases a type of pheromone, a scent that male moths can detect. Some species of moths can detect these pheromones from several miles away. This chemical communication is the main way that moths find each other in the dark.

Once a male moth locates a female by following her pheromone trail, there may be additional courtship behaviors. For example, some male moths will “flutter” or “dance” around the female. This display may serve to further signal the male’s interest and also to show off his fitness.

Finally, if the female accepts the male’s advances, the pair will mate. The specific method of mating varies by species, but it generally involves the male and female aligning their bodies and connecting their reproductive organs. After mating, the female will lay eggs that have been fertilized by the male’s sperm.

In some moth species, males also have various strategies to ensure their paternity, such as mating plugs or substances that prevent the female from mating again. This is a complex and fascinating area of study in the field of insect behavior and evolution.

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By Andrei Ionescu, Earth.com Staff Writer

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