ZQ28

The Latest Buzz Tom McKeag

The Latest Buzz: Could the Mosquito Cause More Good than Harm? It’s summer, and it’s hot, and you have just sat down in your backyard to have a nice cool drink and watch the sunset, until, of course, if you live in certain places with sufficient moisture, you hear that dreaded bugle call of an all-too-familiar insect, the mosquito. You know the party’s over, don’t you? For she will either find and impale you, or you will spend the next twenty minutes of your existence in frenzied watch and fitful conniptions. It is a “she”, you know, and she needs your blood for protein to lay her eggs. She will find you. The mosquito has an intriguing array of mechanisms to find her target, starting with detecting the CO2 plumes from your exhalation within 10 meters, to recognizing the 340 different chemicals given off by your body within 1 meter, to a simple optical system to spot you in that chair, to heat sensors in her antennae that guide her to the warmth of the subdermal capillaries of your exposed skin within 20 centimeters. Imagine being co-pilot as she turns these sensor systems on sequentially and concurrently as you fly ever and ever closer to landing. We humans don’t have a chance!

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Or do we? Plants are masters at manipulating insects for all sorts of reasons and all sorts of ways. They especially do not want to be eaten by insects so have evolved all sorts of secondary metabolites, like the oils from the Lemon Eucalyptus tree, E. citriodora, otherwise known as PMD (p-methane 3,8-diol), that masks odors, or pyrethrins, from Chrysanthemum that repels or kills insects, or the oil from lemongrass, Cymbopogon citratus, that blocks CO2 and impairs the mosquito’s initial homing methods. Pyrethroids, ultimately modeled on the natural compound pyrethrin, are a broad category of divergently structured compounds grouped according to their effectiveness as biocides. They work by locking open the voltage-gated sodium channels in the axonal membranes of nerve cells. With these channels frozen in the open position, no switching in polarity can occur and therefore no sodium ions pass through the membrane to initiate action: the animal is paralyzed. Many of the strongly scented plants, like mint, eucalyptus and pine also contain monoterpenes or isoprenoid compounds within their essential oil that repel animals. Like everything else in nature,