Superhero mosquitoes?

Apparently when I was 5, I asked my mom why the water in the kiddie pool was moving on its own. It was the middle of summer, and the pool had been filled with stagnant water for a while. Confused, she went to take a look. The pool (no wider than 3 feet) was teeming with thousands of swimming mosquito larvae.

Repulsed? She definitely was. I don’t think I was ever allowed to swim in the pool again.

I hope you never have to experience crawling into a pool with a bunch of wriggling mosquito larvae, but they don’t even need that much water to breed.

The artificial pools created when you water your plants are more than enough for female mosquitoes to lay their eggs. These aquatic larvae then become adult mosquitoes, and the females need your blood (they can’t make enough protein on their own) in order to lay their eggs and continue the life cycle.

For dengue especially, there is neither a vaccine nor a cure, and it affects more than 100 million people per year. The mortality rate for this disease is relatively low (20,000 deaths per 100 million infections per year worldwide), and its usually very mild in children, but in adults its symptoms can be debilitating for over than a month. These infections cost countries thousands of dollars a year.

But blood isn’t the only thing that gets exchanged between humans and mosquitoes. Many species transmit human diseases, which reside in the mosquito’s saliva and get injected into a human when the mosquito bites him. Mosquitoes then become the vector for many human diseases, such as dengue, West Nile Virus, yellow fever, and malaria. For many of these neglected tropical diseases (excluding malaria), there are neither vaccines nor cures, and millions of people become infected every year.

The following video does a nice job of highlighting the consequences of dengue and the work Australian researchers have accomplished in restraining dengue. Although it’s two years old, it explains in plain terms the ways in which they use Wolbachia, a bacteria that lives in 60% of the worlds insect species, to stop the spread of dengue fever. To do this they infected Aedes aegypti, the mosquito that transmits the disease, with the bacteria.

The Wolbachia cleared dengue from the mosquitoes’ saliva. When a mosquito bites us, it injects some of its own saliva into our blood, transmitting diseases in the mosquito’s saliva. If the disease, in this case dengue virus, is not present in the saliva, it is not able to jump to the human.

I just can’t imagine having to be the human volunteer that feeds the mosquitoes every day.

A more recent study by the same Australian group found that the mosquitoes infected with Wolbachia were able to successfully establish themselves in a wild population (suburbs in Northeastern Australia).

Effective disease control, and cost efficient too. Let’s hope the dengue-resistant mosquitoes are able to keep their population numbers high so that this technology can be spread to more countries in need.

Photo Credits: www.knowabouthealth.com

Would a world without mosquitoes really be all that great?

I recently stumbled across a relatively old (2010) Nature article discussing whether the eradication of the earth’s mosquitoes would actually be bad for the environment.

From a human perspective, by all means get rid of them. They're pretty annoying.

It's not their fault that they have to bite us, however. Nature gave female mosquitoes the gift of not being able to make enough protein to lay eggs on their own. Our blood has that protein. When looked at the issue from a more ecological standpoint, the eradication of all mosquitoes could have some incredibly negative consequences.

There are over 3,000 mosquito species in the world, and only a handful of these spread human diseases. Granted, these diseases, such as yellow fever, malaria, dengue, and encephalitis cause thousands of deaths each year and put a huge financial strain on developing countries. However, this doesn’t stop us from constantly trying to get rid of them. Granted, the mosquitoes that spread human diseases live around humans, so this is the only side we see of them.

Janet McAllister, a medical entomologist at the Centers for Disease Control and Prevention, is quoted as saying “If there was a benefit to having them around, we would have found a way to exploit them. We haven’t wanted anything from mosquitoes except for them to go away.” I think the first phrase should be reworded to this: “If there was a benefit for humans to have mosquitoes around”. Just because there isn’t a benefit to humans does not mean that the ecosystem as a whole does not benefit from mosquitoes.

Many species of animals rely on mosquitoes as their sources of food, for example the mosquitofish (Gambusia affinis) almost entirely preys on mosquitoes. Many other species rely on insects for their food sources as well: other insects, reptiles, amphibians, spiders, even some birds and bats. While some of these species could potentially switch to eating a different insect without too much ill effect on their fitness, undoubtedly some would suffer.

Removing an entirety of species would have severe unintended consequences that would reverberate upward through the food chain. This picture gives a very basic outline of how complicated a food web could be. Mosquitoes feed on animals, transmit disease (keeping populations in check), and pollinate plants, and their larvae become food for many different species. Mosquitoes are both on the top and on the bottom at many points in the web.

What I’m curious to know is how the question of total mosquito eradication came up. Is it someone’s goal to accomplish this? Regardless it that is true, humans have been trying to control mosquito populations for a long time, and the mosquitoes repopulate incredibly quickly.

Eradicating the entire world's mosquito populations seems like not only an ethical problem but an impractical one as well.

Photo Credits: worldofbiology.wikispaces.com, www.examiner.com

Love Is in the Air

You know that cute musician boy who you always secretly hoped would serenade you and ask you out on a date? Well, maybe I was just having a very high school crush, but the serenade (and the date) never happened. So long, love life. I don’t think it had anything to do with the fact that I never talked to him. Nope. Communication? Nah. Not that important.

Well. Maybe I should work on that.

As it turns out, communication is a pretty important factor in building relationships. Take a lesson from any mosquito. While they definitely can’t talk, they emit tones from their wing beat frequencies that match up with mosquitoes of the opposite sex in their same species.

A 2009 study discovered that male Aedes aegypti mosquitoes are able to hear noises 1200 Hz. Before you question why this news is important at all (and to find out what 1200 Hz sounds like), click here and go to 4:56. Turns out that annoying buzz you hear when a mosquito flies in your ear can be its mating call.

How do mosquitoes hear in the first place? They have an organ called the Johnston’s organ located in the second antennae segment (nearest the head). It’s a mass of sensory cells that can detect wind and gravity and also a prospective mate’s wing beat frequency.

This is particularly helpful in male mosquitoes, which may be identified by their feathery antennae. The antennae are only tuned to the frequency at which females of their species emit sound, and the discovery that the males could hear frequencies of 1200 Hz is 400 Hz above what researchers previously thought was the male’s deafness threshold.

The other (and more applicable) part of the study found that female mosquitoes who have not mated yet are more likely to respond to the male frequency (1400 Hz) than are already mated females, suggesting that mating makes a female less sensitivity to male stimuli.

Basically, once a female mosquito is off the market, she’s off the market. No cheating involved (or at least very rarely).

This could have implications in studies about disease control and could affect sterile male releases of mosquitoes. It would be important to make sure the altered males will be able to attract mates, or else the release of extra mosquitoes would not produce the desired decrease in the wild mosquito population. And if the sterile males are able to mate with a female, she will be less likely to mate a second time with a (possibly) fertile male.

I wish I knew what prompted the researchers to do this study. I really do. I guess love is in the air.

Photo credits: www.news.sciencemag.org, www.sciencephoto.com

Genetic Modification for Disease Control

Genetic engineering isn’t only limited to livestock these days. What about disease control?

A company called OxiTec, founded by Dr. Luke Alphey of the UK, has patents on genetically engineered mosquitoes whose offspring are unable to reproduce. They sell these mosquitoes (and other insects) to customers who want to reduce local insect pest populations for agricultural or health reasons.

OxiTec sells two types of these insects: “Bisex RIDL” and “Female-specific RIDL”. The first means that you release both sexes into the wild, but any progeny the altered mosquitoes have will die at a predetermined stage of the life cycle. The second means that the males carry the fatal gene and pass it down to their offspring. The female offspring die, but the male offspring are able to mate and once again pass on the deadly gene.

Reducing the number mosquitoes, the spreaders of dengue, chikungunya, malaria, etc. will save thousands of human lives each year. Even the website’s tagline reads, “RIDL employs modern technology to provide effective, clean control of insect pests.” Meaning that the toxic, chemical pesticides that the public knows do not need to be used. This seems safe for the environment, right?

Right.

Here’s a 2009 video of Dr. Alphey speaking about his company’s research and products. In my opinion, he does a very good job of explaining the scientific processes in an easy to understand manner. He gives multiple examples about how RIDL helps contain insect pests, and it seems very effective.

With continued releases, this technology keeps insect numbers low and reduces incidence of disease. The New World Screw Worm was highly prevalent throughout North and Central America, but by releasing thousands of sterile male Screw Worms a week, countries save an estimated “$1.3 billion in economic damage each year at a cost of $10 million.” That’s a ridiculous amount. And an incredible way to cut down on the use of insecticides in the environment.

On an unrelated note, and I’m playing Devil’s Advocate here, it is interesting that in the company’s description of current Aedes (the genus of mosquito that spreads dengue, yellow fever, and chikungunya) control methods, it neglects to mention the recent trial completed in Australia in which bacteria-infected mosquitoes were discovered to stop dengue transmission and were successfully released in Australian neighborhoods. Whether the website has not been updated since August 2011 or they intentionally left it out I can’t tell.

I do know that the Australian study, in which researchers released thousands of mosquitoes infected with Wolbachia, a bacteria that stops the spread of dengue, made headlines in many different media due to its success. Hopefully there’s no animosity between the two groups. But it’s never bad to have multiple successful, competing ideas, as long as they both accomplish what they set out to do. Indeed, in the video Dr. Alphey says, “None of this [eradicating diseases] will be done solo; it will all be done with other partners, and in many cases using a combination of approaches, not just the one [RIDL] I suggested.”

This is a very exciting, cutting-edge area of research and I’ll definitely follow the company’s progress.

Photo Credits: www.oxitec.com, www.fohn.net