European Black oil beetle larva lures unsuspecting bees by manufacturing smells that mimic floral scents, new research suggests. The larva then hitches a ride on the bee to its burrow, where it eats the bee’s eggs and pollen, and develops into an adult beetle. This is the first known instance of an animal hijacking the smell of a flower to lure another animal to parasitize it, the study’s authors say.
Larvae of the European black oil beetle (Meloe proscarabaeus) are orange and gather on the tips of plants to attract bee hosts, which they then parasitize. The research team hypothesized that the larvae emit some kind of chemical to attract the bees.
Using chemical analysis, the researchers found that the beetles emit compounds called floral monoterpenoids, the same chemicals that produce the scent of flowers in many plant species.
The researchers prepared a synthetic mix of the compounds in the lab and found that bee species in the wild were attracted to them, supporting the hypothesis that the beetle’s larvae imitate flowers to lure bee hosts.
Ryan Alam, the study’s lead author from the Max Planck Institute for Chemical Ecology in Germany, told Mongabay by email that the team hasn’t identified a specific flower with a scent that matches the floral chemical profile the larvae emit. However, he added that the compounds are known components of the scent of willow flowers, which makes the plants an intriguing candidate.
“Determining the precise floral source (if any!), and understanding how closely the larval scent matches it, would be an exciting next step,” Alam said.
He added that there’s a closely related beetle species in North America that releases chemicals that mimic the sex-pheromones emitted by female bees to lure male bees and parasitize them. This suggests that chemical-based mimicry has evolved in multiple beetle species, Alam said.
The researchers suspect that chemical mimicry may be more widespread in beetles than currently known, but may be much harder to detect than visual mimicry, Alam added, “It is quite possible that similar examples exist in other groups of insects, or even in other animals, but they may have gone unnoticed so far.”
Jim McLean, an evolutionary biologist at Macquarie University in Australia not involved in the study, told Scientific American that Alam’s research “presents a convincing case that the beetle larvae are mimicking flowers chemically, and perhaps visually, so as to deceive and attract bees.”
Banner image: A cluster of European oil beetle (Meloe proscarabaeus) larvae on a blade of grass: Not only could they be mistaken for a flower at first glance, but to wild bees, their smell cannot be distinguished from the scent of many flowers. Image courtesy of Danny Kessler, Max Planck Institute for Chemical Ecology.
