ITHACA, N.Y. -- Naked, immobile and conspicuously colored, the squash beetle pupae would be easy picking for insect predators if they hadn't long ago perfected a science called combinatorial chemistry. In the human world it is a chemical skill that pharmaceutical researchers are still learning.
By variously combining three simple molecules into a veritable arsenal of complex defensive compounds and secreting them through microscopic body hairs, Epilachna borealis pupae can thwart just about anything that would eat them, Cornell University researchers report in the July 17 issue of the journal Science.
"Industrial chemists have only begun practicing combinatorial chemistry in the last five years. They generate a very large number of variations on one architectural theme and test a library of compounds very rapidly for pharmaceutical activity with high-throughput screening," explains Jerrold Meinwald, the Goldwin Smith Professor of Chemistry at Cornell who is one of six authors of the Science article.
"This beetle pupa does the same thing, creating hundreds of deterrent compounds from three simple precursors," Meinwald adds. "Then it skips the screening process in the laboratory and goes straight to the field where the ultimate test is its survival in a bug-eat-bug world."
One of the hundreds of different chemicals produced by E. borealis is a necklace-like structure of 280 atoms forming one single large ring. With no other defenses than this, the beetle pupae are rarely disturbed. Hungry ants, for example, are quickly repulsed by the pupal chemicals and frantically clean the noxious substances from their antennae with special brushes on their forelegs. Within a few days, the pupae metamorphose into adult squash beetles -- and in the process become an agricultural nuisance.