Sunday, August 19, 2007

New mosquito-control hope

Mosquitoes, the first of which arrived in Hawai'i in a sailing ship's water casks in 1826 at Lahaina, are among the more annoying things about living in the Islands.

Now there's hope that something can be done about mosquitoes—something besides fogging communities with pesticides. But more on that later.

All mosquitoes, as most folks know, are not created equal. Different species bite at different times, inhabit different territories, and carry different diseases.

That first mosquito, which arrived now more than 170 years ago was the southern house mosquito, Culex quinquefasciatus. It breeds in the smallest pools of water, including the crotches of plants, from sea level to more than a mile in elevation. Its main threat to the environment is that it carries avian pox and avian malaria. It is believed to be a key figure in the destruction of Hawaiian native birds—perhaps one of the world's most amazing examples of adaptive radiation. It will fly three miles to find a meal, and generally bites in the early evening.

The Yellow Fever mosquito, Aedes aegypti, which also carried dengue fever, showed up in 1892. It's a daytime biter.

In 1896, the Asian tiger mosquito, Aedes albopictus, showed up. It's sometimes called the forest day mosquito. It carries dengue fever. The tiger does fine with pockets of water in rocks and even buckets in your yard. It generally bites during the day, but doesn't fly far, so cleaning out old tires, tin cans and other sources of breeding water will help reduce numbers around the home. It is the most common of day-biting mosquitoes.

The inland floodwater mosquito, Aedes vexans nocturnus arrived in 1962. If you find a puddle in the yard or a water-filled tire depression along the road, look for it there. Good news: it hasn't been implicated in disease transmission. On the other hand, this is the one that bites at night, buzzing in your ear well into the pre-dawn hours.

The bromeliad or pineapple lily mosquito, Wyeomyia mitchellii, a 1981 arrival, appears to be limited to the few teaspoons of water that collect at the base of bromeliad leaves and in cut bamboo. Both this and the floodwater mosquito have not been known from Maui, but are on the other major islands. It is a very small mosquito, and will bite at dusk.

Another dengue-carrier, Aedes japonicus, showed up on the Big Island in 2004. It is a daytime biter, although it will continue harassing people into dusk.

Quarantine officials regularly catch new mosquito species. More than 40 have been stopped, apparently including the 2003 interception of the mosquito that transmits malaria in humans, Anopheles punctipennis.

Hawai'i's 2002 outbreak of dengue fever, with more than 100 confirmed cases, was linked to the Asian tiger mosquito, Aedes albopictus.

And several of the Hawai'i species can carry West Nile Virus.

For information on controlling mosquitoes around your home, see this state Department of Health site on the web:

The recommendations include using aerosol mosquito spray for adults, wearing insect repellent, and either using chemical means or things like mosquito fish to control the larvae in water bodies. Some research has been done , with some success, with using strains of the bacteria Bacillus thuringiensis on mosquitoes.

But to get to the teaser that started this story, Dutch researchers have found a fungus that attacks mosquitoes and can significantly shorten their lifespans.

Writing in the June 2007 edition of “Acta Tropica,” entomologists Ernst-Jan Scholte, Willem Takken and Bart Knols write of the “Infection of adult Aedes aegypti and Ae. albopictus mosquitoes with the entomopathogenic fungus Metarhizium anisopliae.”

(Entomopathogenic is a fancy word that means something that makes insects sick.)

They found that if the mosquitoes landed on a surface contaminated with the fungus, they became infected, and they lived 3 or 4 days, rather than the normal 17 to 18 days.

Would it also work on other mosquito species, and is there a way to use the fungus to control mosquitoes, without making other insects sick? That's still to be determined.

© 2007 Jan W. TenBruggencate

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