Moths Rely On First Impressions In Mate Search, But Grow Indiscriminate

First impressions are important in dating -- whether you’re a human, or a European corn-borer moth. And though both moths and men might start out with an ideal mate in mind, as the search drags on, many seem to be willing to relax their standards.

For moths, the first impression is all about scent. A specific signature of pheromones draws a male moth to the scent of a female in its particular species and strain. But entomologists know that there are lots of hybrid moth strains (similar to subspecies) in nature, which means that wayward males are following their noses (okay, antennae) to different strains. Why do they stray? One group of researchers thinks they have the answer.

Researchers from the Hungarian Academy of Sciences, the Swedish University of Agricultural Sciences, and the University of California, Riverside, examined how male moths followed the scent of a female moth in a wind tunnel. They published their results on Monday in the Proceedings of the National Academy of Sciences.

"What we generally recognize as a distinctive smell -- the scent of a flower or the aroma of coffee -- typically consists of a mixture of many different chemicals," coauthor and UCR entomologist Ring Carde said in a statement Monday. "This is the signature of a particular bouquet -- the presence of a blend of many chemicals often in specific ratios. Our work suggests that it could be the first impression -- the first whiff of odor -- that determines the ability of an insect to recognize that odor mixture."

The researchers found that a male will initially fly toward pheromones released by a female from his own strain. But as he flies, the moth will relax his standards, so to speak.

The key lies in the insect’s head. A moth’s brain has different receptors for each pheromone component, and they all fire at different rates. So as the moth flies through a cloud of alluring pheromones, the input changes, according to coauthor Tuen Dekker.

"To overcome this mismatch, moths rely on the ratio they detected in their first encounter with the plume,” Dekker said in a statement.

Though they’ll initially fly toward a highly matched scent, as a moth keeps flying through a cloud of competing scents, they’ll just take whatever’s available.

"Once male moths lock onto a pheromone plume, they are much less attuned to blend quality," Dekker said. "In other words, males fly even to blends that were initially unattractive, and so can mate with females of different strains that they would not have approached otherwise, explaining why we find hybrid moths in nature."

SOURCE: Karpati et al. “Early quality assessment lessens pheromone specificity in a moth.” PNAS published online April 15, 2013.