By Wendy Langhans
My husband and I drive older cars, without on-board GPS, so when I plan a route, I rely on Google Maps or Mapquest and print two kinds of maps. One map is large scale, showing me the major highways or freeways that will get me from here to there (or at least nearby). The second map is small scale, showing the site I’m looking for, plus nearby cross streets and at least one major highway. Recent studies have found that African malaria mosquitoes (Anopheles gambiae) use a similar zoom/scale navigational technique when searching for one of their favorite food sources - a warm-blooded human being.
The carbon dioxide we exhale is the basis of the mosquito’s “large scale” map. According to this Science News story , “Malaria mosquitoes utilize CO2 from exhaled air” to locate their human victims. But once they get close to their human target, they switch to a “small scale” map. Mosquitoes seek out the spot on a human where they stand the best chance of being undetected until it’s too late. As the Science News story describes it, “In the vicinity of their preferred host, they alter their course towards the human feet.”
So how do mosquitoes switch from one scale of map to another? After all, they don’t carry a sophisticated on-board GPS navigation system, do they? It turns out that they do - and it’s based on smell, not sight.
Odor-detecting nerves cells (olfactory neurons) can be found on the mosquito’s two antennae, mouthparts (maxillary palps) and nose (proboscis). Oderant receptors sit on the surface of these cells and these receptors are designed to detect certain specific chemicals. One type of olfactory neuron has receptors that specifically detect carbon dioxide. When a molecule of carbon dioxide comes in physical contact with this receptor, it triggers the nerve cell to send a signal. This GPS system allows the mosquito to detect a human “tens of meters” away.
But there are other types of oderant receptors, some of which detect smelly chemicals produced by the bacteria living on human feet. And some of these chemicals not only trigger certain olfactory neurons, but they also inhibit the neuron that detect carbon dioxide.
When that happens, the mosquito modifies the scale of it’s GPS system from a “broad scale” map to a “small scale” map and changes course in search of the closest pair of smelly feet.
The moral of this story? When you’re heading off into the wilderness, take plenty of clean socks with you. A bottle of antibacterial hand gel wouldn’t hurt either. And if you hear a faint, buzzy, high-pitched female voice instructing, “Descend now”, get out of there fast.
Upcoming Outdoor Events:
Saturday, March 12 - Sunday, May 29, SCV Search & Rescue Trail Challenge 2011: 12 Weeks/12 Hikes. Click here  for more information.
Saturday, May 14, 1 - 3 PM, Water-Loving Wildflowers at Elsmere Canyon. The small steam in Elsmere Canyon has its own special set of wildflowers. Savor the cool shade and its floral inhabitants on this easy hike. Meet at the Whitney Canyon parking lot. For directions and trail maps, click here .
Saturday, May 14, 10 - 3 PM, Open House and Family Festival at Placerita Canyon. For directions, click here .
Saturday, May 21, 8 - 10 AM, Early Morning Bird Hike at Towsley Canyon. Will you be able to identify the birds you find? Don’t worry, Volunteer Naturalist Roger has plenty of experience to help you out. Let your eyes spy the many birds at Towsley Canyon on this easy walk. Binoculars optional. Meet at the Towsley Canyon front parking lot. For directions and trail maps, click here .
Trail Maintenance Schedule. Come join our volunteers as they help maintain our trails. Contact Steve at email@example.com  for time and place.
Wednesday mornings, May 4, 11, 18, 25.
Saturday mornings, May 14, 28.
For a glimpse of our local flowering plants, check out the Facebook page, “90 Days of Santa Clarita Valley Wildflowers ”.
You can listen to stories like this every Friday morning at 7:10 a.m. on "The SCV Outdoor Report", brought to you by your hometown radio station KHTS (AM1220) and by the Mountains Recreation and Conservation Authority.
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