[Pollinator] Blister beetle larvae mimic desert bees

[Kimberly Winter]

A fascinating article about blister beetle larvae that mimic desert bee 
scent and shape, attracting males to them:

http://sciencenow.sciencemag.org/cgi/content/full/2006/911/3

Hey Honey, I'm No Bee
By Rhitu Chatterjee
ScienceNOW Daily News
11 September 2006

Parasites are renowned for their deceptive dealings with their hosts, but 
the blister beetle takes its subterfuge to a carnal extreme. According to a 
new study, the beetle's larvae attract the males of a solitary desert bee 
using chemicals that mimic a female's pheromones. The ruse allows the 
parasites to hitch a ride on the males and ultimately reach a treasure-trove 
of pollen and nectar that surrounds the female bee's egg.

The blister beetle (Meloe franciscanus) lays its egg at the base of the 
Borrego milkvetch plant. Once the larvae hatch, thousands clamber to the 
tips of branches. The reasons behind these swarms were unknown until 2000, 
when ecologists John Hafernik and Leslie Saul-Gershenz of the Center for 
Ecosystem Survival in San Francisco, California, noticed that the 
aggregation of larvae resembled a female bee. When male bees approached, the 
tiny larvae grabbed onto their bellies. Hafernik and Saul-Gershenz 
hypothesized that chemical cues from the larvae could play a role in the 
males' initial attraction.

Indeed, these chemicals do the trick. In the current study, Saul-Gershenz 
and Jocelyn Millar, a chemist at the University of California, Riverside, 
show that mimicking a female bee's appearance is not enough to lure the 
males: Models of female bees, made of painted aluminum foil, failed to get 
the guys' attention unless they were smothered with extracts from either the 
beetle larvae or female bee heads. A comparison of the extracts revealed 
that both contain similar chemical signatures. In addition, the higher the 
concentration of the extract, the more the males were attracted. This 
suggests that the larvae "cooperate with each other to increase the dose" of 
the signal, says Saul-Gershenz, whose team reports its findings online this 
week in the Proceedings of the National Academy of Sciences.

Once they latch onto the male bees, the larvae hang on till he mates, at 
which point they quickly move on to the female. After mating, the female 
goes to her underground nest to lay a single egg, which--along with nearby 
stores of pollen and nectar--becomes a feast for the larvae.

The authors "have good evidence that they are really on to the chemistry of 
the sex attractant," says Thomas Eisner of Cornell University. Jack Shultz, 
a chemical ecologist at Pennsylvania State University in State College, says 
the evidence is compelling, and he hopes future studies would look into the 
impact of the beetles on the bee population.

~Kim

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Kimberly Winter, Ph.D.
International Coordinator
North American Pollinator Protection Campaign
Internet: www.nappc.org, www.pollinator.org
Ph: (301) 219-7030