Wednesday, August 27, 2014

The Mosquito's Fall Love Song

August is prime mosquito breeding season, and northeast Florida is in the bull’s-eye with over forty species calling this area "home." There are a number of myths about mosquitoes, including the mistaken idea that they can transmit HIV. They can't. There are a number of very problematic illnesses they can transmit, including Eastern Equine Encephalitis (EEE) from the virus (EEEV) by that same name. EEEV can infect both humans and horses. The salt marsh mosquito (Aedes sollicitans) is one vector of transmission, and this particular species is a difficult one to control given its life-cycle.

A. sollicitans is found in salt marshes. Like other female mosquitoes, the salt marsh mosquito needs a protein-rich feeding in order to lay eggs. Typically the female A. sollicitans seeks blood from a mammalian source, including humans and horses. After she has fed she can travel for miles looking for a low-lying, but dry patch of ground in a salt marsh. The eggs need four or five days of dry warm weather, then must be inundated by water that the next very high tide washes in. Eggs laid in the fall can overwinter awaiting the next favorable condition for hatching. The resulting larvae feed and molt several times, then enter a pupal stage before emerging as an adult. Depending upon temperature and other conditions, the mosquito's life cycle can last anywhere from a few days to two weeks. Since the salt marsh mosquito breeds in marshy areas, it is impractical for humans to control its breeding. Mosquito Control Districts, such as Anastasia, use chemical means to reduce populations.

As of this writing, there have been no known human or equine cases of EEEV in St. Johns County. Clay has had several equine cases, despite the fact that there is a veterinary vaccine for the disease. Unlike some species of mosquito, the salt marsh mosquito cannot host the EEEV. It can only transmit the virus after coming in contact with an infected bird. (If A. sollicitans cannot find a mammal, it will obtain blood feeding from a bird.) Because birds act as virus reservoirs, they can serve as indicators that the EEEV is present in a given area, and therefore, transmittable to humans or animals. Typically chickens are used as "sentinels" since they can be sequestered during the summer months and periodically tested for virus antibodies. These "canaries in a coal mine" are our first warnings to take serious precautions against getting bitten. However, precautions are prudent year-round in Florida. So when enjoying this beautiful fall weather on the GTM Research Reserve trails don't forget to bring effective insect repellent and protective clothing!

Now for two weird facts about mosquitoes.
  1. They do not have lungs: they breathe through openings in their chest or abdominal exoskeletons. 
  2. They "harmonize" their wing beats as part of the mating ritual. Yes, that annoying whine is music to a mosquito's ears. In the case of a related species, A. aegypti, the male slows its 600 beats-per-second (bps) while the female increases her 400-bps so they produce a combined total of 1200 bps: the perfect love song. After mating the female will be ready for her "protein drink" - preferably fresh blood. This mating and breeding behavior has inspired some scientists to call it the "Whine and Dine". It's possible that away might be found to disrupt the whining that initiates mating. Perhaps if more mosquitoes were tone-deaf we could reduce the need for our Mosquito Control District's services and still prevent mosquito-borne diseases.

Sources diseases/_documents/2014/week34arbovirusreport-8-23-14.pdf

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