University of Utah study: young moth males go for females and fail

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Lev Bely, 14.06.2012 0:20

Moths, like many other insects, are led by smells when they seek for food, egg-laying site and, certainly, a mate. University of Utah recent research reveals how moth males prepare themselves to take a flight towards females that effuse pheromones. Biologists arranged an olfactory experience in the course of which they blew pheromones about, so the treated moths would begin warming up their flight muscles to take off quickly.

Males found to hurry too much trying to take off before their body got warm enough for a good flight, according to José Crespo, a doctoral candidate who conducted the experiments.

The question is what's evolutionary more advantageous, best start or better warm-up that apparently provides a better flight? It's still to be answered in other researches since Crespo observed only takeoffs. “The important thing is decision-making. This has to do with sensing stimuli that can be visual or olfactory, and responding appropriately. It tells us how animals make decisions,” Crespo said.

Crespo's team worked with Helicoverpa zea moths of Noctuidae family which comprises over 35,000 species. They chose that very species due to it's known as a serious agricultural pest, so it's a good model for unveiling of how its brains transduce scent signals.

Helicoverpa zea caterpillars are commonly named “corn ear worm” thanks to they devour corn, yet they're also known as the “cotton bollworm” or “tomato fruitworm” depend on what crop they feed on. Crespo's experiments can improve nontoxic methods aimed to reduce H. zea reproduction rates without using pesticides.

Each species of this huge family effuses a scent mix that can contain up to five pheromones. “You can imagine with 35,000 species there is a lot of cross talk out there. They are all using similar words, if you will, but arranged in different orders,” said Neil Vickers, senior author on the study and the chairman of the U. biology department. “Males have to be picky when interpreting these pheromonal sentences. Otherwise you can make a mistake, and that can be very costly. If they end up coupling with the wrong species, they become tangled and can’t decouple.”

So males not only have to choose the right female but also should they be “an early bird” when it comes to coupling. Natural selection favors those not procrastinating as to make offspring. Winner is the one who arrives in time and does his best to compete.

Crespo constructed a foot-long wind tunnel and placed one of six scents at the upwind side of the cardboard box propelled by a 1 mph breeze towards males that never coupled before. One of the scents was a common H. zea sex attractant. Crespo observed how much time it took for males to prepare themselves for flight when they warmed up their opposing flight muscles by squeezing those and making them shiver. He monitored changes of their body temperatures recording the process with infrared cameras.

The second stage was to measure males' lifting force at different body temperatures. Crespo placed moths inside a small Styrofoam ball and bound them to a force meter, then made moths take off by pulling the ball down. Curious that the optimal body temperature for a good flight appeared to be about 90 degrees while in the “pheromone” test males attempted to take off, averagely, at 82 degrees.

“Insect flight muscles are among the most metabolically costly in the animal kingdom. In order to fly, you have to use a lot of oxygen and generate the power,” Vickers said. “The decision to take flight after a female odor is not one that would be taken lightly by the moth because it’s expensive.”

The study results published on June 7th in the Journal of Experimental Biology. The research supported by the National Science Foundation and the National Institutes of Health. University biologist Franz Goller is a study's co-author.

The Salt Lake Tribune, http://www.sltrib.com

Photo: José Crespo with one of the H. zea experimental moth, Rick Egan, http://www.sltrib.com

Moth male warming up before flight (University of Utah infrared shoot)