Do you want to beat the bite of mosquitoes? This is a summary of research projects and publications dealing with mosquitoes, mosquito-borne disease, insect repellents, urban wetlands and urban ecology (as well as other Medical Entomology activities) by Dr Cameron Webb (University of Sydney & NSW Health Pathology)
There’s been a swarm of headlines recently about the global decline of insects. Could mosquitoes be disappearing too? Probably not but how would we know?
What about mosquitoes? Sadly, they’re not a group of insects many people would care too much about if they were threatened with extinction.
Some of the most important mosquitoes, those that transmit dengue viruses or malaria parasites, are evading our efforts to eradicate them. For these insects, the insects authorities the world over actively are trying to kill, they’re surviving quite well. They’re becoming resistant to commonly used insecticides and they’re thriving living in habitats in and around our cities.
The reality is that some mosquitoes are probably doing very well , while those potentially under threat are probably those we know least about.
Tracking change in mosquito populations
There are over 300 mosquitoes in Australia. The mosquitoes that bring with them the greatest pest and public health risks are well studied. Mosquitoes such as Aedes camptorhynchus, Aedes vigilax, and Culex annulirostris are nuisance-biting pests and have been associated with outbreaks of Ross River virus disease. Their populations are monitored as part of mosquito control and surveillance programs around the country. But these programs probably won’t reliably pick up declines in lesser known mosquitoes.
There are mosquito surveillance programs around the country that provide information on local mosquito populations to health authorities. That’s how scientists know if this really is the “worst year for mosquitoes ever”! There is little evidence that the major pest mosquitoes are in decline. But these programs probably won’t reliably pick up declines in lesser known mosquitoes.
Mosquitoes under threat?
It is entirely possible that there are mosquitoes under threat.
What about the mosquitoes that specifically feed on frogs, how will they be impacted by declining frog populations?
Mosquitoes that are highly specialised to certain environments or ecological niches or close interactions with wildlife may struggle if their ecosystems are disrupted. Habitat degradation may hit some mosquitoes in much the same way it’ll hit other insects. It won’t end well.
Mosquitoes can be some of the most adaptable animals on the plant. That’s probably why they’ve been such persistent pests. In fact many insects are quite adaptable to change and that’s why we may not be facing an “insect apocalypse” as many headlines suggest.
The reality is, mosquitoes have already been around for millions of years, they’ll probably be around long after. Its just that we could take a few species with us…
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The image at the top of this article is of a carbon-dioxide baited mosquito trap, there were thousands of mosquitoes inside; collected late in 2018 along the Georges River in southern Sydney.
Join the conversation on Twitter, are there any mosquitoes you think are under threat?
There are few places on earth where you can search in water-filled canoes for one of the most dangerous mosquitoes on the planet less than a stone’s throw from tourists posing for selfies alongside their inflatable novelty swans in the nearby lagoon.
Guam is the place to go if you need to tick that off your “to do” list!
I was fortunate to be invited to speak at the Pacific Island Health Officers Association (PIHOA) Regional Zika Summit and Vector Control Workshop in Guam 25-29 June 2017. The theme of the summit was “Break Down the Silos for Preparedness and Management of Emergencies and Disasters in United States Affiliated Islands” and had objectives to critical analyze the regional responses to recent mosquito-borne disease outbreaks while developing policies to strengthening public health emergency response and preparedness systems and capabilities within the region.
The tranquil lagoons of the Pacific Islands may seem a very long way from the hustle and bustle of the busy South American cities that held the 2016 Olympics but just as Zika virus was grabbing the attention of sports reporters everywhere, health authorities active in the Pacific were growing concerned too.
The Pacific has been far from free of mosquito-borne disease outbreaks. Previous outbreaks of dengue, chikungunya and even Ross River virus had struck numerous times. While sometimes widespread, at other times outbreaks were more sporadic or isolated. As is the case for many non-endemic countries, outbreaks are prompted by movement of infected travelers and the prevalence of local mosquitoes.
Across the region there are four mosquitoes of primary concern, Aedes aegypti, Aedes albopictus, Aedes polynesiensis and Aedes hensilli. The greatest concerns are associated with Aedes aegypti and in those countries where the mosquito is present, the risks of mosquito-borne disease outbreak are greatest. For this reason alone, it is imperative that good entomological surveillance data is collected to confirm the distribution of these mosquitoes but also to develop strategies to eradicate, where possible, Aedes aegypti should it be introduced to new jurisdictions.
With a growing interest in developing mosquito surveillance and control programs for exotic mosquitoes here in Australia, it was a perfect opportunity for me to get a closer look at how the threats of these mosquitoes and associated outbreaks of disease are managed.
On the third day of the meeting, vector control took centre stage. A brilliant day of talks from each of the jurisdictions on the disease outbreaks they’ve faced and how they’re preparing for future threats. There were presentations from the United States Affiliated Pacific Islands (USAPI) including Guam, the Federated States of Micronesia (Yap, Kosrea, Chuuk, Pohnpei), the Commonwealth of the Northern Marianas (CNMI), the Republic of Palau, the Republic of Marshall Islands (RMI), and American Samoa.
Hearing from these teams doing their best to protect their local communities from the threat of mosquito-borne disease, with only limited resources, was quite eye opening. There was passion and dedication but each territory faced unique challenges to ensure the burden of disease is minimised.
Just outside the workshop venue were a series of water-filled canoes. Most contained larvae!
There is little doubt that climate variability will have a strong role to play in the impacts of mosquito-borne disease across the region in the future but there are so many other issues that could be contributing to increased risk too. One of the biggest problems is rubbish.
Time and time again, the issue of accumulated waste, especially car bodies and discarded tyres, was raised as a major problem. As many of the key pest mosquitoes love these objects that trap water, treatment of these increasing stockpiles becomes more of a concern. Community wide cleanups can help reduce the sources of many mosquitoes but the rubbish more often than not remains on the island and requires continued management to ensure is not becoming a home to millions of mosquitoes.
It is a reminder that successful mosquito control relies on much more than just insecticides. An integrated approach is critical.
There was a “hands on” session of surveillance and control. Coordinated by PIHOA’s Eileen Jefferies and Elodie Vajda, the workshop was a great success. It provided an opportunity for many to see how to prepare ovitraps and BGS traps (one of the most widely used mosquito traps) and discuss the various considerations for choosing and using the right insecticides to reduce mosquito-borne disease risk. Workshop attendees were also the luck recipients of a selection of cleaver public awareness material produced in Guam, from personal fans and anatomically incorrect plush mosquitoes to Frisbees and mosquito-themes Pokemon cards!
Guam “mozzie” team: Elodie Vajda, Claire Baradi, Michelle Lastimoza, Eileen Jefferies and me
Following the summit, there was a chance to visit the new Guam “Mosquito Laboratory”, newly established as part of the Guam Environmental Public Health Laboratory (GEPHL). I’ll go out of my way to visit any mosquito laboratory but I was particularly keen to see this one as one of my previous students was playing a key role in establishing the mosquito rearing and identification laboratories. Elodie has been doing an amazing job and it was brilliant to geek out with her over some hard core mosquito taxomony as we tried to ID a couple of tricky specimens. [Make sure you check out our recent paper on the potential impact of climate change on malaria outbreaks in Ethiopia]
Mosquito-borne disease in the Pacific isn’t going anywhere and it’s important that once the focus fades from Zika virus, dengue and chikungunya viruses will again take centre stage and their potential impacts are significant. With the added risks that come with gaps in the understanding of local pest and vector species, the prevalence of insecticide resistance among local mosquitoes, climate variability and a struggle to secure adequate funding, challenges lay ahead in ensuring the burden of mosquito-borne disease doesn’t increase.
A modified version of this article appears in the latest issue (Winter 2017; 12(1)) of Mosquito Bites Magazine, (a publication of the Mosquito Control Association of Australia)
Back in 2015, I had an article published at The Conversation on why some people are more likely to be bitten by mosquitoes than others. It is one of the most commonly asked questions I get whenever I give public talks (or friends and family are quizzing me at summer BBQs).
This article was incredibly successful and has currently been read by approximately 1.4 million people. That is a lot of people. Hopefully the science of mosquito bites has got out there and actually helped a few people stop themselves or their family being bitten by mosquitoes!
The warm weather is starting to arrive here in Australia so I am sharing this once more for those wondering why they’re always the “mosquito magnet” among their friends…
Health Check: why mosquitoes seem to bite some people more
There are up to 400 chemical compounds on human skin that could play a role in attracting mosquitoes. sookie/Flickr, CC BY-SA
There’s always one in a crowd, a sort of harbinger of the oncoming mosquito onslaught: a person mosquitoes seem to target more than others. What is it about these unlucky chosen few that makes them mosquito magnets?
There are hundreds of mosquito species and they all have slightly different preferences when it comes to what or who they bite. But only females bite; they need a nutritional hit to develop eggs.
Finding someone to bite
Mosquitoes are stimulated by a number of factors when seeking out a blood meal. Initially, they’re attracted by the carbon dioxide we exhale. Body heat is probably important too, but once the mosquito gets closer, she will respond to the smell of a potential blood source’s skin.
Studies have suggested blood type (particularly type O), pregnancy and beer drinking all make you marginally more attractive to mosquitoes. But most of this research uses only one mosquito species. Switch to another species and the results are likely to be different.
There are up to 400 chemical compounds on human skin that could play a role in attracting (and perhaps repulsing) mosquitoes. This smelly mix, produced by bacteria living on our skin and exuded in sweat, varies from person to person and is likely to explain why there is substantial variation in how many mozzies we attract. Genetics probably plays the biggest role in this, but a little of it may be down to diet or physiology.
One of the best studied substances contained in sweat is lactic acid. Research shows it’s a key mosquito attractant, particularly for human-biting species such as Aedes aegypti. This should act as fair warning against exercising close to wetlands; a hot and sweaty body is probably the “pick of the bunch” for a hungry mosquito!
Probably the most famous study about their biting habits demonstrated that the mosquitoes that spread malaria (Anopheles gambiae) are attracted to Limburger cheese. The bacteria that gives this cheese its distinctive aroma is closely related to germs living between our toes. That explains why these mosquitoes are attracted to smelly feet.
But when another mosquito (such as Aedes aegypti) is exposed to the same cheese, the phenomenon is not repeated. This difference between mosquitoes highlights the difficulty of studying their biting behaviours. Even pathogens such as malaria may make us more attractive to mosquitoes once we’re infected.
Researchers are trying to unscramble the irresistible smelly cocktails on the skins of “mosquito magnets”. But the bad news is that if you’re one of these people, there isn’t much you can do about it other than wearing insect repellents.
The good news is that you may one day help isolate a substance, or mixes of substances, that will help them find the perfect lure to use in mosquito traps. We could all then possibly say goodbye to topical insect repellents altogether.
Attraction or reaction?
Sometimes, it’s not the bite as much as the reaction that raises concerns. Think of the last time the mosquito magnets in your circle of friends started complaining about being bitten after the event where the purported mosquito feast took place. At least, they appear to have attracted more than the “bite free” people who were also at the picnic, or concert or whatever.
But just because some people didn’t react to mosquito bites, doesn’t mean they weren’t bitten. Just as we do with a range of environmental, chemical or food allergens, we all differ in our reaction to the saliva mosquitoes spit while feeding.
People who don’t react badly to mosquito bites may think they haven’t been bitten when they’ve actually been bitten as much as their itchy friends. In fact, while some people attract more mosquito bites than others, there’s unlikely to be anyone who never, ever, gets bitten.
The problem is that people who don’t react to mosquito bites may all too easily become complacent. If you’re one of them, remember that it only takes one bite to contract a mosquito-borne disease.
Finally, there is no evidence from anywhere in the world that there is something you can eat or drink that will stop you being bitten by mosquitoes. No, not even eating garlic, or swallowing vitamin B supplements.
Perhaps if we spent as much time thinking about how to choose and use mosquito repellents as we do about why mosquitoes bite our friends and family less than us, there’d be fewer bites all around.
I thought I’d celebrate the 20th anniversary of one of my favourite movies, Jurassic Park, by posting on, what is arguably, the most famous mosquito in cinematic history.
As most people probably already know, the “science” of the story revolves around the cloning of dinosaurs from DNA samples obtained from prehistoric mosquitoes. The DNA was purportedly extracted from blood meals contained within these mosquitoes that had been trapped and preserved in amber. Even though studies have suggested that DNA wouldn’t survive long enough to assist in making “Jurassic Park” styled dinosaurs a reality, modern molecular techniques are quickly improving and may make the impossible a little more possible in the future.
If we can improve the technology enough to make this happen, could the research team who receives the multimillion dollar grant please go to the trouble of hiring an entomologist? You don’t want to make the same mistake as the team led by entrepreneur John Hammond.
I’m not just referring to the creation of nasty people eating dinosaurs. If you’re hunting around for mosquitoes in amber, you’d better pick the specimens that may actually contain blood!
The screen shot above is taken from a scene in the movie (see YouTube clip below). The scene provides some background to the process behind dinosaur DNA capture. It has already been pointed out elsewhere that the mosquito specimen depicted in the video is a male mosquito. Male mosquitoes don’t feed on blood.
Only female mosquitoes feed on blood, they need the nutritional hit to develop their eggs. Mosquitoes take blood from a range of vertebrates. Birds, mammals, frogs and reptiles. In theory, there is no reason why a mosquito wouldn’t bite a dinosaur. Blood meal analysis of mosquito populations in Florida during an outbreak of West Nile virus revealed that a number of mosquitoes were feeding on alligators (Alligator mississippiensis).
The problem isn’t just that the mosquito depicted in the video is male, the type of mosquito shown doesn’t feed on blood at all!
Not all mosquitoes need a blood meal. There is a group of mosquito species that belong to the genus Toxorhynchites. These are large, very beautiful mosquitoes that often have a metallic appearance. They are really the “good guys” of the mosquito world. Their immature stages are predatory. They are typically found in natural or artificial water holding containers such as buckets, bird baths, tree holes or discarded tyres. They tend to move in and eat through some of the other pest mosquitoes found in these types of habitats such as Aedes aegypti and Aedes albopictus. These mosquitoes spread pathogens such as the dengue and chikungunya viruses.
Notwithstanding their size, a Toxorhynchites is most easily identifiable by their long bent proboscis. Compare the photo below to the screen shot from the Jurassic Park video. See that bent proboscis? The bent proboscis assists in nectar feeding by this mosquito. (as an aside, if you look at the shot of the “Jurassic Park” mosquito, you can see that the wings of the mosquito are actually squished down along the side of the abdomen. The “wings” shown in the mosquito are fake. There are no wing veins)
Lets give credit to John Hammond and the team at International Genetic Technologies, perhaps it is samples from these mosquitoes that they were able to use to clone the prehistoric plants that were growing throughout Jurassic Park?
If you’ve decided to go out and hunt down some dinosaur DNA, best look out for mosquitoes that actually feed on blood!
Do we know that mosquitoes were even buzzing about with the dinosaurs?
There is strong evidence, both preserved specimens in amber as well as fossils, that mozzies have been about since at least the Cretaceous Period. A paper by Poinar et al. (2000), in their description of a small mosquito named Paleoculicis minututs from a sample of Canadian Cretaceous amber, provides references to almost 40 references to mosquitoes in the fossil record. Paleoculicis minututs was thought to have dated back to 66-100 million years ago but the oldest known record of a mosquito is Burmaculex antiqusdescribed from Cretaceous Burmese amber (89.3-99.6 million years ago).
There are mosquitoes related to these two species flying about today. There are thought to be almost 40 species belonging to the genus Culiseta. They’re generally considered to be associated to cooler-temperature climates. We have a few species in Australia such as Culiseta frenchii, Culiseta hilli, Culiseta inconspicua and Culiseta litteri. They tend to be associated with ground pools in forested areas. Although they will bite humans, they are rarely considered pests and have not been associated with the transmission of pathogens locally. However, related species are thought to transmit both Eastern and Western equine encephalitis virus in North America. Mosquitoes belonging to Culiseta, although they will bite mammals, are generally thought to prefer blood meals from birds.
While it may be fun (and nerdy) to spot mistakes like this in movies, it is nice to be given an opportunity to dig back through the literature and have a closer look at some of the more unusual mosquito species and their place in the fossil record. Perhaps we’ll find some mosquitoes in Australian fossils someday too. I’m not aware of any mosquitoes identified from fossils found in Australia but there are research projects investigating insect specimens in amber. Fingers crossed.
UPDATE. Wouldn’t you know it! Just as I hit “publish”, I notice that a similar story is doing the rounds today, something must be in the water!!! Joe Conlon has been reported in a few places reporting the same issue. Some more coverage here.
UPDATE [15 October 2013]. Some more “mozzie fossil” news is making headlines today with the fossil of a blood-engorged mosquito in oil shale from northwestern Montana, USA, has been described in a recently published paper!
Newly described blood-filled mosquito fossil (The National Museum of Natural History, Washington via Nature)
The discovery of a mosquito (Culiseta sp. Culicidae) fossil clearly displaying an engorged abdomen from a recent blood meal has provided more evidence that mosquitoes were feeding on vertebrates as far back as 46 million years ago. Not only does the specimen look engorged, mass-spectrometry analysis of the specimen identified heme, the oxygen-carrying group of hemoglobin in the host’s blood. The study, publish in Nature, describes the discovery but also details the “extremely improbable event” that this fossil was created, let alone discovered tens of millions of years later! While discoveries like this still aren’t going to bring back the dinosaurs, they do confirm hematophagy in the fossil record. I wonder what other specimens are out there?
Update [1 December 2014] Jurassic World repeats the mistakes of the past…
A screen shot from the Jurassic World trailer…is this supposed to be a mosquito?
November saw the release of a trailer for the new movie in the “Jurassic” franchise, Jurassic World. As well as attracting plenty of attention from fans and media about the movie, it also attracted plenty of interest from dinosaur lovers and entomologists. There was a great post by Dr. David Steen on some of the errors spotted by wildlife biologists and paleontologistsand Morgan Jackson put together a nice piece on the entomological inaccuracies of the trailer (it is a crane fly, not a mosquito, locked up in that amber). Despite all of this, perhaps the biggest issue to have arisen is the purported unauthorized use of illustrations in accompanying promotional material.
“Shut up, Scientists! Always have to ruin everything with facts and accuracy.”
It would be silly to get REALLY upset about the mosquito/crane fly mix up but there was no shortage of people pointing out the mistake, you’d think they’d fix it this time around (unless there is a gag we’ll get in the movie about crane flies and non-biting mosquitoes). However, any opportunity to point out some scientific inaccuracies provides an opportunity to raise awareness of genuine scientific knowledge. I’m regularly called up to investigate “giant mosquito” problems….that almost always turn out to the crane flies (they don’t bite BTW).
I’ll be heading along to see the Jurassic World monsters in 2015 but perhaps I’ll take the kids back to the museum to learn about dinosaurs and some of the other extinct Australian mega fauna for a hit of real science.
Now, about that light saber in the trailer for “The Force Awakens”….
Perhaps if we spent as much time thinking about how to 
Beat the Bites: Mosquito Research and Management 