May 29, 1998 COLUMBUS, Ohio -- Researchers at Ohio State University have uncovered some curious behavior among common household dust mites that may one day suggest a better means of exterminating them.
Researchers have long known that dust mites die without adequate moisture. Now a study has revealed that males of the species employ a special trick to survive dry spells -- they cluster together to conserve water.
If researchers can figure out what makes dust mites cluster, they might be able to find new ways to kill these microscopic insects, which excrete proteins that can trigger asthma and allergy attacks in people.
Glen Needham, associate professor of entomology, explained how dust mites are vulnerable to changes in moisture. “Because of low humidity, the average home is not a friendly place for mites -- it’s like a moonscape,” he said. “One of a dust mite’s major challenges is to keep from drying out.”
“We think that when dust mites cluster together, moisture gets trapped between them, so they’re better able to survive low humidity in groups than they would be by themselves,” said Emmett Glass, research associate in the Department of Internal Medicine and leader of the study. The work appeared in a recent issue of the journal Experimental & Applied Acarology.
Researchers have known for about 30 years that dust mites snack on naturally-shed human skin cells, and about 25 years ago, Ohio State entomologists discovered that dust mites don’t drink water, they suck molecules of it from the air. They also lose water from the surface of their hard outer shells. That’s why dry environments are particularly inhospitable to dust mites.
During a routine examination of laboratory colonies of mites, Glass noticed that males tended to cluster together while females traveled solo. Along with Jay A. Yoder, assistant professor of biology at The Illinois College, the Ohio State researchers decided to test whether clustering prevented water loss.
They briefly exposed the mites to very low humidity, allowing some of the males to cluster while keeping other males in isolation, and then compared water loss between the two groups. Isolated males lost nearly twice as much water as their clustered counterparts: 2.63 percent of their total body moisture versus 1.48 percent.
Glass said that mites continue to cluster even when moisture levels in their environment become favorable.
“Humidity in our lab colonies is high enough for the mites to survive quite well, but the mites cluster anyway. We think they expend less energy gathering water that way,” said Glass.
Why should clustering be more beneficial to males than females? The researchers said that males don’t seem to be as hearty as females. Females live for about 90 days, approximately twice as long as males.
How male mites find each other is also somewhat of a mystery. Glass speculates that pheromones may play a role. Dust mites secrete a number of different chemicals, but nobody knows for sure whether any of them are pheromones. Scientists have thus far only identified the role of one of these chemicals -- a compound that inhibits mold growth.
“A number of mites and ticks use pheromones and other chemicals,” said Glass. “They have a whole series of chemical cues, for finding mates for example, or for sounding an alarm. It seems reasonable to think that dust mites utilize chemical communication too.”
If dust mites do indeed use pheromones to find each other, researchers may be able to interrupt the clustering instinct by interfering with these pheromones. Then mites that are unable to cluster could dry out and die on their own, eliminating the need for traditional mite-killing insecticides.
“Typical places to find mites are the mattress, and the carpeting next to the bed, because the bed is where we spend the majority of our time -- at least 8 hours a day sleeping, so we lose a lot of skin cells there,” said Glass. “The average person sheds enough skin cells every day to feed thousands of mites for a month.”
Needham said that most homes have dust mites, but the mites usually don’t pose a threat, except for people with asthma or allergies who react negatively to the mite droppings. Most people don’t even notice that the mites are around.
Glass said that clustering might contribute to the dust mites’ prevalence. “Mites are not supposed to be able to survive below 50 percent humidity,” he said. “And heating a home in the winter will cause the humidity to drop below 50 percent, but the mites will survive anyway. We think clustering in addition to entering a kind of hibernation is how they’re able to do that.”
Glass and Needham did this work as part of a larger Ohio State project that is seeking new ways to rid homes of the allergens that trigger asthma attacks.
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