Pick-Up-Lines: Even for Beetles They're all About Timing

The longhorned beetle was long thought to be the cologne connoisseur of the insect world, selecting mates based on smell alone. However, like a frat house drowning in Axe body spray, sometimes all the males in a region smell the same. So how do lady longhorns know who's 'Mr. Right?' According to a new study, timing is everything.

"Smell is an underappreciated sense in people - but when you talk about insects, many 'see' their world in chemicals," researcher Robert F. Mitchell, of the University of Arizona, recently explained.

An associate in the department of neuroscience and the Center for Insect Science, Mitchell has long known that the great majority of insect communication is done through pheromones. In some bugs like beetles, mantids, and even among spiders, "the most common thing they say with pheromones is, 'I'm looking for a mate'," he said.

In this way, how males and females smell can been seen as pick-up-lines in the insect and arachnid worlds. Experts generally like to determine what characterizes each species' own lines, so to speak, in order to understand what makes it 'sexy' for their mates.

However, simple curiosity aside, there are practical reasons for investigating this.

"Pheromones are promising alternatives to pesticides as a means of monitoring and controlling pests," Mitchell explained.

A prime example of this would be baiting traps with the right pheromone. That's how experts have been combating several pest beetles, including the invasive Asian longhorned beetle in the eastern US, and the California prionus that ravages hop fields in western states. 

However, Mitchell and his colleagues had determined in past work that, contrary to the norm, many longhorned beetles seem to be attracted to the same 'pick-up-line' despite radical differences in their species. This could spell trouble for trapping, as harming local populations while hunting invaders is never good for an ecosystem.

It also simply didn't make sense. After all, naturalists weren't witnessing frequent inter-species mating among these insects.

"We asked, 'How do they tell each other apart if they're all producing the same thing?'" Mitchell said.

Perhaps taking cues from the human dating world, the researchers decided that timing might have a lot to do with it. After all, delivering a pick-up-line at the wrong time for one girl may work with another. It's then not absurd to assume that beetles are similar, with timing preferences changing from species to species. (Scroll to read on...)

To see if they were right, the researchers set out special rotating traps that could separate the beetles based on the time of day they were collected. The end result then wouldn't be a smorgasbord of beetle species all on one plate, but instead clearly divided and uniform groups.

And that's basically what the researchers saw. They found some species visited primarily in the daytime, some came in the early evening, and others came at night. Other experiments revealed that the 11 species also searched for mates at different times in the spring.

Finally, the team found that species completely overlapping in time would add additional scents that put off other species while attracting their own.

Still, timing and those subtle differences don't always work, but Mitchell adds that this may not be a bad thing. He explained that we really don't want Asian longhorns finding Mr. Right in the US always, so if their females are frequently confused and drawn to incompatible males, that means the species is reproducing less than it could be.

"Our native beetles might be unwittingly defending us against invaders," he said.

Results of the study are detailed in full in the Journal of Chemical Ecology.

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