Love at First Bite

Many people have had the unpleasant experience of being swarmed by mosquitoes on a summer night while their companions went undisturbed. New research has confirmed that it's not their imagination--mosquitoes do prefer some people over others.

University of Florida entomologist Jerry Butler and colleagues asked nine people, about half of whom considered themselves attractive to mosquitoes, to wrap their forearms with an artificial skin for four hours to pick up their scents.

The researchers then placed the "skin" into a device containing hundreds of mosquitoes that measured how often the insects bit it over an eight-hour period. Some people were clearly attractive to the bugs, while others were clearly repellent, the researchers found.

Scientists are still trying to identify all the substances that make some people more appealing than others to mosquitoes. But "aged sweat," and substances in many face creams, hair sprays and cosmetics, seem irresistible to them, Butler says.

So someone trying to become less attractive to mosquitoes could bathe often and avoid those products, he says. Another strategy, Butler says, is to see if there's someone nearby who appears even more attractive to the bloodsuckers, and stand next to them.

Another Reason to Diet

Evidence has been mounting that animals that eat extremely low-calorie diets tend to live substantially longer. Now, researchers have found a clue to why that may be the case, raising the possibility they eventually may be able to use the information to extend longevity in humans.

Tomas A. Prolle of the University of Wisconsin at Madison and colleagues studied the impact of a very low-calorie diet on 6,347 genes in mice as they aged. The genes of mice that consumed 24 percent fewer calories seemed less likely to show the signs of aging. Genes involved in tissue repair, for example, seemed to remain more active, the researchers report in the Aug. 27 issue of Science.

The researchers plan to study monkeys and people to see if the findings hold true for those species. The hope is that drugs could be developed to mimic the beneficial effects of caloric restriction.

Trauma and Sex Determination

Trauma appears to cause more girls to be born than usual.

Dorthe Hansen of the John F. Kennedy Institute in Denmark and colleagues studied the records for all Danish women who gave birth from Jan. 1, 1980, until Dec. 31, 1992, and identified every woman who was exposed to some kind of traumatic event in the year of the birth or the previous year.

Women who had experienced trauma, such as a death or serious illness, were significantly more likely to give birth to girls, the researchers report in the Aug. 28 issue of the British Medical Journal.

"Psychological stress related to severe life events may alter the sex ratio through changes in sexual activity, changes in hormones around the time of conception, reduced semen quality, or an increased rate of early male abortion," they speculate.

An Upside to Plane Crashes?

People who survive airplane crashes seem to end up in much better mental health than most people, according to a new study.

Gary Capobianco of Old Dominion University and Thanos Patelis of the College Board studied 11 men and four women age 31 to 67 who survived airplane crashes. Compared with eight people who travel frequently by air but were never in a crash, the accident survivors scored better on tests measuring anxiety, depression and stress, the researchers reported at a recent meeting of the American Psychological Association in Boston.

The researchers acknowledged that their findings may have been skewed because only people who had not been too traumatized by their experience would be willing to participate. But it might be, the researchers speculate, that surviving a crash gives people greater perspective on life.

A Theory May Be Eroding

There's been a lot of concern that modern farming practices have been causing fertile topsoil to erode quickly. A new study, however, finds that may not be the case.

Stanley W. Trimble of the University of California at Los Angeles analyzed 140 years' worth of information about sediment in a watershed made up of the Cook Creek River and its tributaries in Wisconsin. Overall, soil erosion in the watershed has been steadily decreasing since the 1930s, and has dropped to just 6 percent of what it was during the Dust Bowl years, Trimble reports in the Aug. 20 Science. The findings indicate that recent efforts to stem soil erosion have been working.

Some experts, however, questioned whether the Cook Creek area is representative of what's happening elsewhere in the country.

The Efficient Bicycle

Bicycles are surprisingly efficient machines, according to a new analysis.

James B. Spicer of Johns Hopkins University and colleagues used an infrared camera and a computer-controlled bicycle drive chain to measure the amount of energy wasted. By detecting the amount of heat generated by friction as the chain moved through the sprockets under various conditions, the researchers determined that a bicycle drive chain could be up to 98.6 percent efficient.

"This was amazing to me, especially when you realize the essential construction of this chain drive hasn't changed in more than 100 years," Spicer said.