Beetles find randy path to beehives

Newly hatched blister beetle larvae from the Mojave desert in the US use an intriguing method to invade and destroy bee colonies. They clump together in masses mimicking the shape and scent of female bees and trick amorous males into picking them up. The male Habropoda pallida bee might think he is on for a good time, but ends up carrying away larvae, next passing them on to real female bees who in turn deliver the dangerous larvae to their nests.

This kind of co-operative behaviour by hundreds of larvae is virtually unknown in the insect world except among bees and ants and was identified by Dr John Hafernik and Dr Leslie Saul-Gershenz of San Francisco State University.

"While co-operative behaviour is common among highly social insects such as bees and ants, it has never been reported in blister beetles. What's more, until now no other insect has been known to use co-operative behaviour to mimic other species," Dr Hafernik said.

The researchers describe the larval activity as a "remarkable mode of host-finding" and they don't exaggerate. Adult blister beetles are named for their defensive mechanism of releasing a drop of blood laced with the chemical cantharidin which causes severe pain and blistering upon contact with the skin. They lay their eggs in the deserts of Nevada and when the larvae emerge they immediately climb to the top of the nearest plant stem where hundreds then form wriggling masses that roughly mimic the size and shape of a female bee.

If a passing male falls for this subterfuge, the larvae use pincherlike limbs to catch hold of the hairs on the duped bee. The male then deposits larvae on female bees during subsequent mating attempts.

Any larvae that make it back to the nest with the female then play havoc with the hive. They help themselves to the pollen and nectar and any bee eggs also make for a nutritious lunch. Once installed they are difficult to eliminate.

The researchers believe that the larvae use more than appearance to fool the male bees, emitting a scent similar to that of a female bee. They tested this theory by placing model larval masses next to actual larvae but the bees were not interested. "The male bees ignored the models completely but hovered or tried to land on groups of [larvae] even before they were formed into a bee-like mass," stated Dr SaulGershenz who is studying the chemical cues.