SCIENCE NOTEBOOK

Only four zoos outside of New Zealand have successfully bred kiwis, and only three U.S. zoos exhibit them. The birth marked just the third time in the National Zoo's history that a kiwi has been hatched. The first, in 1975, was the first to occur outside New Zealand. The second was in 2006.

Kiwis typically mate for life, and both parents care for the egg. Chicks are born fully feathered and able to survive on their own.

There are five species of kiwi, and all are unique to New Zealand. The North Island brown species is New Zealand's national bird. Although kiwis have existed in New Zealand for more than 30 million years, only about 24,000 North Island brown kiwis are believed to remain in the wild.

-- Rob Stein

DEET Fools Mosquito's 'Nose'

For most people trying to avoid being eaten alive by mosquitoes, it is enough to know that DEET works. But for scientists and marketers hoping to invent or sell an even better bug repellent, the goal is to find out why DEET works.

Now researchers at Rockefeller University in New York have solved a big part of that longstanding mystery, finding that DEET blocks a highly specific molecular pathway that tells a bug's brain what it is smelling. In particular, it interferes with an insect's ability to smell 1-octen-3-ol -- a telltale ingredient of human breath -- and the scent of lactic acid, an odoriferous hallmark of sweat.

N,N-diethyl-meta-toluamide, or DEET, is the most widely used insect repellent in the world and was developed 60 years ago by the Agriculture Department and the Army. Among the many six-legged pests that find the stuff offensive are mosquitoes, including the species that transmit malaria -- a disease that kills 1 million people every year -- yellow fever, dengue and West Nile fever.

Leslie B. Vosshall and colleagues measured the electrical pulses coming from nerves in the mosquito's olfactory organ and found that DEET blocks a molecular smell receptor known as OR83b, which detects key components of human sweat and breath.

Experiments in fruit flies confirmed the importance of that smell receptor and its susceptibility to interference by DEET.

The discovery means that scientists can start large-scale screenings of chemicals, including some that might be formulated into more pleasant creams, to see if they are as good or better at blocking OR83b.

Details were published Friday in the journal Science.

-- Rick Weiss