Beetles Seduce Bees to Survive

Sept. 12, 2006 — Clusters of blister beetle larvae mimic female bees in an act of deception so successful that male bees try to mate with them and bring them back to the nest. There the larvae live in the lap of bee luxury by receiving free food and shelter, according to a new study.

Scientists believe the behavior is the first known example of cooperative, aggressive mimicry among insects. Cooperation is involved since the larvae stack up on top of each other and work as a unit to mimic just one female bee. The act is aggressive because, once in the bee’s nest, the sneaky parasites either eat the egg or the bees' hard-won food.

The act of mimicry goes beyond appearances, explained Leslie Saul-Gershenz, who worked on the study, published in the Proceedings of the National Academy of Sciences.

"The blister beetle larvae cooperate to emit a pheromone of sufficient signal strength that mimics the female bee," she said.

Saul-Gershenz, director of conservation at the Center for Ecosystem Survival in San Francisco, and coauthor Jocelyn Millar studied the insects at Kelso Dunes in California’s Mojave National Preserve. The act of seductive mimicry, they found, happens in four steps.

The worm-like larvae first emerge from eggs at the base of plants, such as grass blades, and then pile into a ball before shinnying up the plant.

The insects then release their secret weapon — a chemical similar to the female bee pheromone — and wait. With the release of this "perfume" plume, the baby beetles reach out toward any nearby male bee.

"The larvae extend out the upper part of their body and their front legs, which have specialized claws that are adapted for grasping," Saul-Gershenz explained to Discovery News.

The beetle babies then latch onto the back of the male. When the male mates with an actual female bee, it unknowingly transfers its larval cargo to her. The larvae hitch a ride on the female to the nest, where they grow and mature, and the whole cycle begins again.

The deception appears to have evolved as a survival tool for the blister beetle, which live in California's harsh Mojave desert environment where temperatures reach well above 100 degrees Fahrenheit.

"Walking to a nest would therefore be extremely difficult for a 2 mm-long (.078-inch) larva," said Saul-Gershenz.

Tom Zavortink, a researcher at the University of California at Davis’ Bohart Museum of Entomology, told Discovery News that he read some initial reports about the blister beetle larvae several years ago, so he was not surprised by the findings.

"Scientists expected that a chemical cue might allow the larvae to fool male bees, so this new research confirms the suspicions," Zavortink explained.

Saul-Gershenz said she and colleague Jocelyn Millar are currently studying how the larvae cooperate with each other, including the possibility that some individual larvae might serve as leaders within the clusters.