How male tobacco budworm moths found their perfect cologne

Many plants and animals will do whatever it takes to reproduce, from “wingmen” dolphins to pee sniffing giraffes to daisies that trick flies into pollinating with them. Now, a team of scientists have identified a specific blend of pheromone chemicals and a newly unveiled aphrodisiac that male moths use during courtship. The findings were published on August 1 in the journal Current Biology and are showing more detail on this complex blend of chemicals that are used in the short-range communications between male and female moths.

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The male pheromone mixture used in mating was first discovered almost 35 years ago, but the male moth aphrodisiac found in this study is a chemical called methyl salicylate. It is derived from plants and is emitted when herbivores move in to attacks and eat them. Methyl salicylate acts as both a healing mechanism in the plants and as a cry for help to the enemies of the herbivores eating the plants, to alert them that there is potential food nearby. 

The moth family in this study feeds on roughly 350 plant species across North and South America, including the tobacco budworm, the corn earworm, and the fall armyworm. Male Chloridea virescens moths–also called the tobacco budworm moth–use methyl salicylate in their pheromone blend that the team on this study say likely helps the male show dominance. Basically, this natural perfume is proof that the moth was able to defeat the plant’s defenses and could be considered a way of signaling that it is a 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,” study co-author and North Carolina State University entomologist Coby Schal said in a statement. “This interaction gives females some insight into a particular male’s history.”

The female moths will begin the mating process by emitting an attraction pheromone blend made up of fatty acids over a longer range of distance and the males respond to these cues by flying closer to the females. Once they’re close enough, the males emit their own unique blend of pheromones made up of different alcohols. The females then use the male’s blend to help them decide whether the male is partner material. 

In the study, the team used a method where chemical compounds are separated in a controllable oven called gas chromatography, to determine the chemicals that make up the male pheromone blend. Some of these ingredients were not found in the initial characterization first made by scientists over three decades ago. 

[Related: The alluring tail of the Luna moth is surprisingly useless for finding a mate.]

They discovered that the methyl salicylate elicited a huge response from the females in the lab, notably because the female moth antennae have two smell receptors specifically for picking up this chemical. 

The team was also able to reduce the amount of methyl salicylate the males emitted and saw that mating success suffered. When these males then received smaller quantities of methyl salicylate, their mating success rates returned to normal, demonstrating how the chemical works more like an aphrodisiac.

Additionally, the team found small amounts of methyl salicylate in moths that had been eating an artificial diet in the lab, but those caught in North Carolina soybean fields had large amounts of the chemical. The chemical was stored in their hairpencils, male organs that emit their special mating pheromone blend. Adding the chemical into the diet of male moths in the lab through a sugar water drink that mimicked nectar demonstrated how male moths incorporated the chemical and sequestered it in their hairpencils. When they were encouraged to vigorously court females, those hairpencils had lower amounts of methyl salicylate since the males used a lot 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,” Schal said. “Males may have evolved sexual signals that match the sensory bias exhibited by females in responding to methyl salicylate.”