This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
As spring creeps up on us, most of the country looks forward to basking in the long-awaited sun. People skip work. College kids skip class. School kids finally get to play outside without snow boots, well maybe not this year. But for some pockets of the country, the prospect of late sunsets and warm summer nights is coupled with the not so pleasant emergence of mosquito season. And even before the year sinks into the summer months, mosquito control workers are faced with tough questions regarding the most socially and environmentally responsible ways to control mosquito populations in their communities.
The Florida Keys is one of those pockets, perhaps one of the worst in the country.
If it weren't for mosquito control, “you wouldn't live here, there'd be no tourism,” says Coleen Fitzsimmons, a biologist at the Florida Keys Mosquito Control District. Fitzsimmons and the rest of her mosquito-fighting team work around the clock to keep Florida’s southern most neighborhoods habitable for residents and tourists and to try to prevent disease.
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The effort is comprised of 3 offices and about 75 employees, made up of domestic inspectors, field inspectors, administrative staff, researchers, and even aircraft staff. About a quarter of the group, the domestic inspectors, has the expansive job of visiting every single home in the Keys area every 3 months (there are about 9,400 households in Key West alone and only 12 domestic inspectors assigned to that area), leaving informational pamphlets and looking to remove water – everything from old cisterns and unmaintained pools to misplaced buckets and backed-up drainpipes.
Luckily for the workers going house to house, the Keys district mosquito control has been supported and paid for by Keys residents since the 1950s, which means less doors shut in their faces. According to Florida Statutes, nuisance mosquitoes are considered a public health threat, says district assistant director Andrea Leal. “They can suffocate people, they’ve killed cattle in Ft Meyers,” Fitszimmons is quick to add as she sits in her Key West office, jar of mosquitoes in hand.
“We are just trying to control the spread of disease and make living down here bearable. We are not in the elimination business. That would be impossible, ” says Fitzsimmons. Because the Everglades is a protected area, the team only has access to about 5% of Monroe county.
For well over 50 years, taxpayers have funded helicopters, airplanes, and all other resources used to control mosquitoes in the Florida Keys. Most of their work is preventative – getting rid of hidden or forgotten still water sources – but they have found creative ways of controlling existing mosquito nurseries.
For example, the team has found what they call their “unpaid employees”, the Gambusia, a native fish that lives in brackish water and feeds on mosquito larvae and other organic matter. The team breeds the 3 cm silver fish in a large outdoor tank outside their building and then they release the fish into abandoned hot tubs and swimming pools.
While these mini mosquito-predators can transform any dilapidated Jacuzzi into the outdoor aquarium you've always wanted, for most of mosquito-fighting history, DDT has been the human army's weapon of choice. DDT can wipe out mosquito populations and their larvae for up to four months at a time. Between 1948 and 1952, for example, disease-carrying mosquitoes were eradicated from over 15 South American countries using DDT.
Michael Doyle, who recently moved to the Florida Keys to become director of Keys Mosquito Control, has built a career out of finding ways to control mosquito populations without resorting to the most effective, yet most environmentally hazardous method of using DDT. And he is no rookie when it comes to dangerous disease outbreaks. He witnessed firsthand the effects of the West Nile Virus that started in 1999 and took 2 years to spread throughout the United States, killing 146 people and infecting thousands of others.
It was during Doyle's previous job in Colorado where he presided over 1 and worked in 2 of the 10 districts worst affected by West Nile. Most people wouldn't think of Colorado as a state with a big mosquito problem, but it had some very intense breeding pockets and just the right conditions for West Nile to spread.
As Doyle explains, “You have just the right combination of mosquito species, people outdoors, and birds all in a very small area interacting.” He calls it the Oasis effect. The irrigated west is made up of small towns with farmlands all around them. And small plots of vegetation. In Doyle's “oasis”, people and animals and vegetation make just the right equation for a West Nile outbreak.
The intense breeding grounds of Doyle's “oasis” affected not only people but wildlife, targeting birds, and cyclically, the rest of the food chain. By 2002, just shy of 4500 birds from 111 different species had been positively identified as having died from West Nile. Even raptor sanctuaries were severely affected.
West Nile brought to light limitations in controlling populations in container breeding mosquitoes, non-native mosquitoes that breed in buckets and small, often hidden water sources, mosquitoes that are rarely a natural or useful part of ecosystems where they dwell. “When West Nile came, we realized we don't have many tools to treat thousands of little tiny containers. It takes hundreds of hours. You can imagine how long it takes to go from door to door to door, not to mention conversations and getting in and out of doors, and the cost.”
The Aedes Albopictus, a particularly aggressive species of mosquito, also known as the Asian Tiger, has shown just how quickly and vastly an invasive mosquito can spread with human transport as its vehicle. It’s commonly accepted among the mosquito-fighting community that the species came to the US in tires. Now the albopictus, which is known to bite mostly during the day while children are outside playing, is prominent in the entire Southeastern quarter of the United States, parts of Texas, and it's recently become a problem in California.
In 2009, mosquito control faced a special dilemma with yet another virus, Dengue. By 2010 there were 66 reported cases in the US. Likely there were more actual cases. Because Dengue has similar symptoms to other viruses and food born illnesses, affected people may not know they have it and doctors may not necessarily know to test for it.
The main culprit in this recent outbreak, Aedes aegypti, is what Doyle and his team call an “urban mosquito” – a mosquito that lives in and around people's homes in small containers. In fact, 99% of mosquitoes that carry Dengue fever live in people’s houses, says Fred Gould, an NC State entomologist who won a 5 million dollar grant for his work in genetic pest management.
Even the most effective and expensive modern mosquito control methods, like Bacillus thuringiensis israelensis (Bti) a bacteria-based larvacide, which is environmentally gentle and targets only black flies and mosquitoes, frequently misses the small and often hidden breeding grounds of the Aedes aegypti. In samples of different mosquito species taken in and around homes, 2% is considered to be the maximum acceptable percentage of the Aedes aegypti species. This past summer, researchers measured proportions of up to 38%.
When it comes to people's attitudes toward mosquitoes, the answer is more or less unanimous. Gould compares mosquitoes to rats, “ If you asked people in New York what they think of getting rid of rats, what do you think their answer would be?”
If mosquito control was a part of a political platform, it might be the one thing red states and blue states (and Florida) could agree on. Most citizens would vote to get rid of them completely if they could. And, of course, like most issues, there'd be questions from worried environmentalists, the voice of the probable political minority in this hypothetical case. What would fish and dragonflies and bats eat? What would happen if ecosystems were disrupted in such a drastic way?
All of these questions and more are exactly what Michael Doyle faces everyday, as he looks to carry out the first US testing of genetically modified mosquitoes, in a project starting, well, one of these days now….
Doyle was intrigued when he first got a call from Oxitec, the British company that has found a way to breed genetically modified male mosquitoes for the purpose of reducing disease carrying mosquito species. Oxitec got good results in trials in other countries like the British Cayman Islands and Malaysia. Doyle and Oxitec saw great potential in holding similar trials in the US under the scrutiny of US regulatory agencies.
But the experiment has been delayed for months now seemingly because of an ambiguity in jurisdiction - exactly which government office would oversee it.
If and when the trial starts, it would take from 4 to 6 months to carry out.
Doyle would put up a small, temporary building outside the main mosquito control facility. In it would be columns of racks like what hold the baked goods in a grocery store, except on these racks he'd grow tens of thousands of genetically modified mosquitoes. Researchers would then separate the males and females, kill the females as pupae, and allow the males to emerge into adults before sending the 5 to 10 thousand adult mosquitoes into the field.
This insect control technique is not entirely new. Since the 1970s we've used the Sterilized male technique, as an alternative to pesticides, to control fruit flies, rampant pests in agriculture. In this experiment, however, the modified males would breed with normal females, creating sterile offspring, who would not reach maturity.
In the field, there are two ways of seeing which mosquitoes are genetically modified and which aren't, and how the population is changing. One, researchers can simply sprinkle fluorescent powder on the male mosquitoes before releasing them. Secondly, the modified mosquitoes could also have a fluorescent gene in them called a marker gene, used a lot in fruit flies. “That doesn't seem to worry too many people because it's been used for so long that it's a stable gene,” says Doyle with some relief.
Then the special mosquitoes pass the gene to their sterile offspring – larva that glows for researchers as they count the modified offspring bred from their trial mosquitoes. The whole idea is looking into the proportion of neon green to grey. Once the modified population gets to 50%, or half the survey sample glows under florescent light, the entire Aedes Aegypti population tilts and starts to fall.
Some have questioned the trial from an economic standpoint, wondering if the project holds any true potential. But Oxitec's past work is exactly what attracted Doyle to the idea. In a similar trial recently finished in the Cayman Islands, for example, researchers saw an 80% reduction in just 2-3 months from achieving the necessary release numbers. Aedes Aegypti was dramatically reduced and, as far as researchers can tell, not replaced by another disease-carrying species such as Aedes Albopictus.
The possibility that one eradicated dangerous species would merely be replaced by another is a hypothetical downside to the experiment. Luke Alphey from Oxitec explains that the monitoring systems they used in that trial, BG Sentinels and ovitraps, would certainly have detected this had it occurred.
To clear up some other initial concerns, the Aedes Aegypti cannot physically mate with other mosquitoes. This modification technique used in the Keys experiment would target one and only one genetic line of mosquito, the Aedes Aegypti, a carrier of Dengue fever (and Yellow fever) in South Florida.
While Doyle and his team do administer mosquito control for nuisance mosquitoes, they are not looking to eradicate all mosquitoes or native, major food source mosquitoes from their natural habitats. On a Florida Keys warm, late winter’s day, Doyle is more than eager to confront these issues head on in the midst of his buzzing Key West office.
“The black salt marsh mosquito is the mosquito everyone gets bit by here. We have those by the billions, literally the billions, If we were planning on permanently removing THEM from the environment, I'd be very, very hesitant to authorize that because of the food source issue... In the United States there are several hundred species of mosquitoes. In Florida, there are about 77 species. This is ONE of all of those.”
Additionally, Doyle has faced criticism from environmental groups like Friends of the Earth who question whether Doyle was purposefully withholding information about the exact location and amount of mosquitoes that would be released. While Doyle concedes his lack of exact numbers may seem a bit suspect, he vows he is hiding no secret plans. “If I was someone in the public who wasn’t familiar with mosquito field studies, I’d think, ‘Whoa, why wouldn’t they won’t tell us how many mosquitoes are being released?’ But from this side of the desk, I’d say, ‘It’s obvious why they aren’t giving an exact number. The number is based on the wild population of mosquitoes, and that number likely to change before the test begins.’”
Doyle says he probably won't know the exact number until a week before. First, they will do trappings to see how many Aedes aegypti show up on average in their trial area (right now a few square blocks in and around the historic Key West cemetery). Once he estimates roughly how many of these mosquitoes live in the area, Doyle will release in genetically modified males 10 times the number wild males he has found. In other words, the goal is to adjust the population, so there are 10 genetically modified Aedes aegypti males per each wild Aedes aegypti male in the field, before eventually seeing entire population drop.
Still, there are some even more murky issues that Doyle has to address. “There have been two concerns about that and I want to make sure I am completely open about all this. Like any biological system, it's not seamless, it's not perfect.” Doyle speaks of the potential of releasing a genetically modified female (only females bite) into the field.
When scientists are sorting the males and females, male mosquitoes are smaller than the females are. So if researchers grow a bunch of mosquitoes in a pan, the males, when they are ready to emerge, are smaller than the females. The females are larger, because they have to carry the eggs. So they are sorted by size, they are put into a sieve. All the small males fall through the sieve and the females get stuck. The males then get dropped into a water tank and emerge as adult mosquitoes.
“Well, occasionally, you'll have a very small female who just didn't get enough to eat,” explains Doyle. “Figure about one in three thousand of those pupae will be a female.” The estimated number of renegade mini females who make it to this stage in the experiment is only 1 in 1,500 or .06% and of that .06%, even less will survive in the natural hardships of the wild.
The estimated number of renegade mini females who make it to this stage in the experiment is only .03 % and of that .03%, even less will survive in the natural hardships of the wild, but the fact that the number is not zero has some citizens worried.
But, the fact that the number is not zero has some citizens worried. “It takes it from 'I cannot get bit', to 'I MIGHT get bit by one of these GMO females', and people don't want to hear 'might'.” Although the threat of getting bit by the one courageous female survivor, if there is one, is extremely statistically unlikely – the truth is you'll probably get bit by a shark first – Doyle can still understand why the public is concerned. “The chances of any one person getting bit by one of these GMO females are very, very low, but it's very hard to explain that to the public. And I don't know, if I wasn't an entomologist, that I'd take the time to figure that out.”
“What if it bites me and because it makes its offspring sterile, what if I have children?” Doyle is bombarded with questions being asked through various lenses, filtered by differing understandings of genetics. He has heard questions from “If it's affecting another mosquito how will it affect me?” to more plausible worries like, “Will the bite of that mosquito cause allergies that another mosquito wouldn't, because it has different proteins in its saliva?”
Doyle maintains that he will not go forward with any type of experiment that endangers his fellow Floridians. “The data I am going to get on paper is that the saliva of one of those mosquito is identical to the saliva of a normal mosquitoes out in the street now,” he says. “It's a public image problem more than a real medical problem.”
For now, he waits to see who will oversee the experiment. “If we get approvals, and if there's nothing that I find out between now and then that concerns me, we could gear up to do it probably in about 2 months,” says Doyle with a type of muffled hopefulness.
Until then, we may not be able to answer all such questions about the hows, whys and shoulds of mosquito control, but we can at least answer one age-old question; what actually attracts mosquitoes to people? Is it sweet blood? Is it body temperature? Is it raspberry body lotion or coconut oil?
The truth is the first thing mosquitoes sense is carbon dioxide. This is how the traps work, in fact. They release carbon dioxide which attracts the mosquitoes to what they think is a person or animals exhale [similar to wasps and hornets]. Then it's a combination of body temperature and skin chemistry. Mosquitoes like blood vessels closer to the skin, and most of all, lactic acid, which is produced in higher amounts when we exercise. So in truth, mosquitoes have not a sweet tooth, but a sour tooth, or proboscis, to be more precise.