Larvae respond to mate-attracting pheromones

By Susan Milius

Web edition: September 6, 2012
Print edition: October 20, 2012; Vol.182 #8 (p. 17)

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A cotton leafworm caterpillar turns out to have some grown-up chemistry for detecting adult female come-hither odors long before developing the winged body form that can actually mate.

Credit: E. Jacquin-Joly

Caterpillars way too immature for actual sex turn out to detect and take an interest in adult sex pheromones.

Caterpillars of the cotton leafworm moth (Spodoptera littoralis) don’t have working sex organs. They’re just long, black-green larvae eating as much as they can before transforming into the completely different body shape and lifestyle of an adult moth. Yet these caterpillars can sense, and appear to like, the adult sex pheromone of their species, an international team reports September 4 in Nature Communications.

“This is a funny fact because sex pheromones are supposed to be for sex,” says coauthor Emmanuelle Jacquin-Joly of the French agricultural research agency INRA in Versailles. Adult female moths release puffs of these chemicals, and males catching a whiff — sometimes from considerable distances — sniff their way through the night to the female.

Evolution may have repurposed some chemistry in this species, Jacquin-Joly and her colleagues propose. What means “come hither” to adult moths may indicate something quite different, perhaps “here’s food,” to a youngster, she says.

She began looking for a cotton leafworm caterpillar pheromone response after another lab found that larval silkworm antennae make the adult-style proteins required to bind molecules of adult sex pheromones from the air and shuttle them to nerve cells. Young silkworms didn’t seem to use the information, but Jacquin-Joly wondered if young cotton leafworms, with a much broader diet, might respond differently.

It turns out that cotton leafworm caterpillars also carry proteins that can bind adult sex pheromones of their species, Jacquin-Joly and her colleagues discovered.

Researchers didn’t find the next compounds they’d expected to see in the pheromone-handling chain, but recordings from caterpillar nerve cells showed that those cells responded to the odor. Also, caterpillars tended to crawl toward a whiff of pheromone and were more likely to investigate food if it smelled like sex pheromone.

Jacquin-Joly hypothesizes that adult females may scent their eggs or the plants where the eggs are laid with the pheromone. A newly hatched caterpillar thus might get a clue that the plant makes fine food.

One of the most exciting parts of this work, says insect molecular biologist Kevin Wanner of Montana State University, is its potential to lead to new tools in pest control. Sex pheromones have been helpful for luring adults to traps or baits, so he wonders if there will be ways to trick pesty youngsters, too.