Many longhorned beetles, such as this Neoclytus mucronatus, attract mates by exuding a sex pheromone. For some species, success also requires exuding their signature perfume at just the right time of day and year. (Credit: Robert F. Mitchell/U. Arizona)

beetles

Beetles use ‘right time’ cologne as a come-on

A longhorned beetle’s sexy scent might make a female perk up her antennae. But when the males of several species all smell the same, a female can’t choose by cologne alone. For them, timing is everything.

“We found that beetles that produce the same pheromone are active at different times of day—and that beetles that are active at the same time of day produce different pheromones,” says Robert F. Mitchell, a research associate in the neuroscience department and the Center for Insect Science at University of Arizona.

beetle trap
Researchers used rotating traps to study the beetles. (Courtesy: Hanks laboratory/University of Illinois at Urbana-Champaign)

In addition, the team found that some of the beetle species that used the same pheromone stayed true to their species by segregating their mating activity by season of the year.

Many animals use chemicals called pheromones to communicate.

“Smell is an underappreciated sense in people—but when you talk about insects, many ‘see’ their world in chemicals,” Mitchell says. “The most common thing they say with pheromones is, ‘I’m looking for a mate.'”

Scientists generally expect each insect species to have its own signature perfume to attract suitable mates. When an insect emits its unique sexual attractant, potential suitors can come a-courting from hundreds of yards away.

However, the family of longhorned beetles presents a puzzle: many species use the same pheromone. The situation seemed to contradict the generally accepted idea of one species-one pheromone.

Pest control

Once researchers figured out the various beetle species sent out their scent signals during different parts of the year and at different times of the day, it all made sense.

“Our research provides a framework for understanding how insects that produce the same pheromone can produce separate signals,” Mitchell says.

Research on insect pheromones has practical applications, as well, Mitchell says. “Pheromones are promising alternatives to pesticides as a means of monitoring and controlling pests.”

For example, by baiting traps with the appropriate pheromone, scientists can detect pest insects and monitor their movements. In the western US, pheromones are used to combat a longhorned beetle known as the California prionus that is a pest on hops.

Using pheromones also can reveal the presence of destructive invasive species such as the Asian longhorned beetle.

Beetle party

As part of his doctoral research at the University of Illinois at Urbana-Champaign, Mitchell studied the chemical attractants for dozens of species of longhorned beetles native to deciduous forests of eastern North America.

The beetles bore into the woody stems of dead shrubs and trees. He later focused on 11 species all attracted to the same chemical. When he and colleagues put traps baited with that pheromone out in the woods, after 24 hours the traps contained “a big multi-species party.”

Initially, Mitchell and his colleagues were baffled. Such a multi-species party didn’t make sense, because mating outside one’s species doesn’t result in viable offspring. “We asked, ‘How do they tell each other apart if they’re all producing the same thing?'” he says.

The team had been using traps that collected all the beetles attracted in a 24-hour period.

Lawrence M. Hanks, senior author of the study that is published in the Journal of Chemical Ecology, learned about a rotating trap that could separate beetles by the time of day they entered. That setup allowed the scientists to test whether different species were attracted only at certain times of day.

Invader defense

By using the rotating traps, the researchers found some species visited primarily in the daytime, some came in the early evening, and some came at night. Other experiments revealed that the 11 species also searched for mates at different times in the spring.

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

Some exotic longhorned beetles such as the Asian longhorned beetle have been introduced to the United States in packing materials such as wooden pallets.

If an invasive species used the same pheromone as a complex of native species, the chemicals emitted by the natives might prevent the invaders from finding suitable mates, Mitchell says. “Our native beetles might be unwittingly defending us against invaders.”

Other researchers from University of Illinois at Urbana-Champaign; University of São Paulo, Brazil; and University of California, Riverside contributed to the study. lphawood Foundation of Chicago, the US Department of Agriculture, the National Institutes of Health, and CAPES-Foundation-Brazil funded the work.

Source: University of Arizona

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