Why do mosquitoes seem to bite some people more?

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

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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.

Only females bite because they need a nutritional hit to develop eggs.
Sean McCann/Flickr, CC BY-NC-SA

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.

The ConversationPerhaps 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.

Cameron Webb, Clinical Lecturer and Principal Hospital Scientist, University of Sydney

This article was originally published on The Conversation. Read the original article.

 

Five things to do (and three to avoid) to beat the buzz of bedroom mozzies

MosquitoRepellents_childarm_webbHere are some tips to beat the buzz of summer mosquitoes and stop those sleepless summer nights! (also some things to avoid!)

1. Stop making a home for mozzies in your backyard

Tip out, throw away or cover any water holding containers in the backyard. This includes buckets, bottles and bins. Mozzies can make even the smallest amount of water home. Don’t overwater your plants, the water sloshing about the pot plant saucer is perfect for mozzies. Empty and refill your bird bath once a week. Tip out water collecting on top of tarpaulins covering boats and trailers. Make sure your rainwater tank is properly screened.

2. Keep the mozzies outside

Check the screens on your windows and doors. Any holes or gaps where mozzies can sneak through? Fix them. You don’t have screens? That’s just plain silly. Fly screens on windows should be standard in every home. Lets the breeze through but keeps the mozzies out. There are lots of great flexible screening options for outdoor areas too so keep them in mind if you want to get more out of your outdoor spaces (with fewer bites).

3. Sleep under a net

Want to recapture that holiday romance of your trip to that malaria endemic tropical destination? It is true that sleeping under a net will keep mozzies away, nets treated with insecticide are even better. However, unless you’ve got a gap between the net and your skin, mozzies will just land and bite straight through the net!

4. Plug in a smokeless mosquito coil

Burning a mosquito coil next to the bed in an enclosed room isn’t a good idea. There are some nasty compounds produces as the coil burns and best not be breathing that in all night. You’re better off with a plug-in vaporizer (often called mozzie zappers – they heat a pad or reservoir of insecticides to kill mozzies in the room).  There is no evidence that they pose a health risk to humans but if you’re in any way concerned, just plug them into a timing device, set it for the first few hours after sunset. By the time it switches off, any mozzies hiding out under the bed will be dead.

5. Move the air around

Sure you could blast the air conditioning and keep the bedroom cold enough to stop the mozzies but why not just switch on a fan. Whether it is a ceiling fan or bedside oscillating fan, a bit of air movement will both disperse the carbon dioxide you’re exhaling (and attracting mosquitoes) and also disrupt the flight of mosquitoes. They’re fragile insects and anything more than a gentle breeze will knock them about.

 

And here are three thing NOT to do….

1. Don’t worry about repellent

Topical insect repellents work great but they’re not something you should be putting on before you go to bed. It isn’t that they’re doing you any harm, its just that they won’t last the night. Most formulations will give you around 4-6h protection normally but it will probably rub off on the bed sheets before it starts to fail anyway. Mozzies are great at detecting a chink in our insect repellent armour so will target in on those little gaps.

2. Don’t fall for urban myths

There is nothing you can eat or drink that will stop you being bitten by mosquitoes. Nothing. Not bananas, not garlic and not taking huge amounts of Vitamin B. If there was something out there we could eat or drink to repel mosquitoes, our pharmacies and supermarkets would have shelves stocked with “mozzie repelling pills” all summer.

3. Don’t plant mosquito repellent plants

There are a few plant species out there that are sold as “mosquito repelling” or “mozzie blocking” but they don’t work. Filling your herb garden or planting out your backyard won’t stop the mozzies. It is true that the essential oils and other extracts from some of these plants have some mosquito repellent attributes, the whole plants don’t. Keep in mind that for many of these plants, particularly tea-trees, they define some of the most productive mosquito habitats along the east coast of Australia. The mozzies don’t seem to mind!

I hope you can stay bite free this summer and get a good nights sleep. What else have you tried to beat the bite of mozzies this summer? Join the conversation on Twitter.

Want to learn more about the amazing world of Australian mosquitoes? Check out “A Field Guide to Mosquitoes of Australia” out now through CSIRO Publishing. Over 200 pages containing a pictorial guide to almost 100 different mosquitoes along with tips on beating their bite and protecting your family from the health risks of mosquitoes. You can order online or through your favourite local bookstore or online retailer.


Read more at The Conversation: Are mosquito coils good or bad for our health?


Read more at The Conversation: What can I eat to stop mosquitoes biting me?


Read more at The Conversation: The best (and worst) ways to beat mosquito bites



 

 

10 things to love about mosquitoes!

Mozzie_illustrationI was recently invited by Associate Professor Chris Buddle (McGill University, Montreal Canada) to contribute to his SciLogs blog, Expiscor. With the brief to produce a series of ten interesting facts about mosquitoes, it would be easy to concentrate on their public health significance. “Ten potentially life threatening pathogens or parasites transmitted by mosquitoes” would have been an obvious choice! However, instead of going down that path, I chose the less obvious route and decided to go with “Ten Things to Love About Mosquitoes“!

Please follow the link to read about some of the fascinating, and potentially ecologically important, things to love about mosquitoes; from singing sexy love songs to cleaning up ant vomit to cooling down hot drinks to pollinating plants. Haters love to hate but how about some love for the mosquitoes that aren’t all that bad….

Why not contribute to the conversation on Twitter? Tell me what you love about mosquitoes….

You can also follow Chris on Twitter @CMBuddle, or check out his wonderful blog at http://www.arthropodecology.com

 

 

 

What could radio-tracking mosquitoes tell us?

News that Australian scientists are about to start a study of bee behaviour using tiny sensors attached to the insects created headlines around the world. Why not, it is a neat story and there is no doubt a need to better understand bees and the threats they face from human activity, parasites, disease and a changing climate. The researchers have already flagged the potential for this methodology to be adapted to studying mosquitoes, what could we find out…if the technology works.

The research team at CSIRO will be attaching sensors (approximately 2.5×2.5mm) to the thorax of 5,000 honey bees in Tasmania. As described in the media release, these sensors act like the “e-tags” in our cars that are used to pay road tolls. An array of detectors will record the movement of those bees with sensors attached. The data could then be used to generate complex maps of bee movement throughout the environment.

Lead author on this “swarm sensing” study, Dr Paulo de Souza, has already flagged the possibility that this technology could be adapted to the study of mosquitoes. There is no doubt that the current size of the sensors would need to be reduced (and there are probably some practical issues to solve regarding the appropriateness of field based sensors when it comes to mosquitoes) but, if that can be done, what questions could we answer if we could microchip mozzies?

How far do mosquitoes fly?

An obvious question but one that has been thoroughly investigated already. Understanding how far mosquitoes disperse from local habitats has implications for nuisance biting and mosquito-borne disease management.

The best example of how an understanding of dispersal assists mosquito-borne disease management is found in Far North Queensland where QLD Health manages dengue outbreaks. When a case of dengue is identified by local authorities, mosquito control is undertaken within a 200m radius of the property. This ensures that any mosquitoes that may have bitten an infected person will be killed before they have the opportunity to infected more people. Understanding how far the “dengue” mosquito flies will assist in allowing authorities to target mosquito control activities.

We don’t need a high tech solution to find out this information. There is a long history of mark-release-recapture experiments measuring dispersalpopulation size and how mosquitoes interact with the environment. You don’t necessarily need to microchip the mozzies, all you need is a few grams of fluorescent powder.

I’ve be part of a couple of mark-release-recapture experiment. My favourite was an investigation into the dispersal activity of dengue mosquitoes in Cairns, Far North Queensland. We marked mosquitoes with a fluorescent powder, released them, and then set a network of traps. All specimens collected were then returned to the laboratory and scanned under a UV light to detect any marked mosquitoes. The results of this study not only assisted the development of strategies to manage dengue outbreaks but this information also assisted the development of a number of research projects (including the Eliminate Dengue program).

The major draw back in mark-release-recapture experiments is that once recaptured, that is the end of the individual mosquito’s contribution to the study. You are only provided with limited information. A simple snap shot. The information provided allows measurement of how far a marked mosquito has travelled from the release point but what if the “stops” along the journey are more important than the distance travelled?

The Saltmarsh Mosquito (Aedes vigilax) (Photo: Stephen Doggett)

The Saltmarsh Mosquito (Aedes vigilax) can travel up to 20km from larval habitats and mark-release-recapture experiments have recorded active movement within 3-5km for saltmarsh and mangrove habitats (Photo: Stephen Doggett)

Where do mosquitoes lay eggs?

In the study of mosquitoes that transmit dengue and chikungunya viruses, where eggs are laid can be critically important. Mosquitoes such as Aedes aegypti and Aedes albopictus lay eggs almost exclusively in artificial containers. Much work has gone into determining the preferred types of containers and the factors that drive egg laying behaviour but we can always learn more.

Mosquitoes “tagged” could be tracked between various types and locations of potential egg-laying sites. What types of habitats are mosquitoes most likely to visit? Is the location of these habitats important (e.g. are containers located in the shade more productive than those in full sunlight?). The better we understand these associations, the better we’re able to assess dengue risk.

With Aedes aegypti exhibiting “skip-oviposition” (i.e. not all eggs are laid in a single container), the ability to track multiple mosquitoes across a range of habitats could provide some valuable information. There has already been much research into this phenomenon using a range of techniques (including this recent study incorporating molecular analysis of specimens) but there are plenty of questions left unanswered. Traditional methods may help identify locations where eggs are laid but how many other sites are visited by mosquitoes where eggs are not laid? This information may be critically important.

Understanding how mosquitoes select the containers where eggs are laid is important for targeted mosquito control strategies (either treatment of containers or removal of containers) or to help in the development of more effective “oviposition traps”.  These traps can then be used as either surveillance or control devices. The technique may also help identify “cryptic breeding sites” that are difficult to identify using traditional surveillance methods.

Tracking movement of the malaria vector Anopheles gambiae in response to odors and heat. Could “microchipped” mosquitoes provide insights into this behaviour in the field? (PLOS)

How do mosquitoes hunt down blood?

The Great White Shark can purportedly detect a single drop of blood in an Olympic-size pool section of ocean. How sensitive is a mosquito to the carbon dioxide exhaled from a potential host? Do mosquitoes sit and wait for a plume of carbon dioxide to float by or do they fly around trying to detect a plume and then fly to the host?

It would be fascinating to see the long and short range flight patterns of “tagged” mosquitoes in response to potential blood meal sources. Do they react differently in response to the “smell” of humans or animals? How do they approach a host?

Researchers have already been working towards answers to these questions using various strategies. Mathematical models have been developed to determine how mosquitoes respond to hosts and cameras in wind tunnels have helped create 3D “maps” of mosquito movement.

Understanding how mosquitoes find and approach a host may help improve the design of mosquito traps. I often find that when collecting mosquito traps in the morning, some species are buzzing about and biting me but they’re not represented in the actual trap collections. Are they approaching the trap differently? In the last decade or so, there have been studies that demonstrate that sucking mosquitoes up into a trap, as opposed to blowing them down, can change the species composition collected. Understanding how mosquitoes approach, and are either collected or not collected in, these traps would be a great outcome of being able to “track” mosquito movement.

In which bedrooms do mosquitoes bite?

In the study of mosquito-disease outbreaks, particularly malaria, it would be useful to understand how many people are potentially bitten by individual mosquitoes. In particular, the spatial and temporal distribution of infective and uninfected mosquitoes and the environmental factors that influence that distribution. Models have been developed to investigate elements of these issues. With more detailed information on how mosquitoes may move around indoors, between rooms within a dwelling or between dwellings in small villages it may be possible to better understand how mosquito movement is influenced by bed nets or residual insecticides.

The great benefit in being able to “track” mosquitoes electronically is that it could be a way of collecting data passively. By that I mean you don’t need to lure, catch or kill specimens. As in the examples regarding egg-laying behaviour, being able to track the spatial and temporal activity of an individual mosquito over time would provide some valuable information. Variability in host-seeking behaviour in response to bed nets or other control strategies has been identified as a critical factor.  It may also provide some insight into host-seeking behaviour without relying on the need for human landing collections.

Some mark-release-recapture studies have provided insights into the movement of malaria vectors from the local environment into villages. The ability to track these movements more specifically, particularly in relation to the availability of hosts, vegetation and other physical/chemical factors will assist in public health risk assessment and the development of control strategies. Perhaps building design could be refined to reduce rates of malaria?

Where do mosquitoes take a nap?

This may sound silly but it could actually be incredibly useful in developing targeted residual insecticide treatments. The identification of resting sites has been the focus of many studies (here is one from South America) and is generally most commonly undertaken through “vacuum sampling” habitats (but a wide range of methods may be used). This technique will help identify locations where mosquitoes are currently resting but it is a little trickier to work out where they came from and where they’re going from those resting sites.

Take this example. That mosquito buzzing about your head at night keeping you awake (most probably the brown house mosquito Culex quinquefasciatus), did it enter your room that night, the previous night, or did it sneak in during the day and take refuge under your bed? While this mozzie may just be a mild nuisance, understanding the resting behaviour of mosquitoes that transmit pathogens will assist control activities. When and where would be the best place to use insecticides to ensure a good nights sleep?

With increasing scrutiny being placed on the use of insecticides in the environment, understanding where applications of residual insecticides are most effective will help balance mosquito control and environmental conservation objectives. For example, to get the most control with least insecticide application, should products be sprayed in the canopy of trees or in the leaf litter below? What surfaces on the outside or inside of homes are most likely to be favoured by mosquitoes? Is the resting behaviour of mosquitoes influenced by the presence of insecticides?

What do male mosquitoes do?

This may not have a great impact on mosquito-borne disease management but it could provide some idea of the ecological role of mosquitoes. What do male mosquitoes do? They’re generally not collected in the carbon dioxide baited traps commonly used to collect female mosquitoes. You can collect them with sweep nets or aspirators but that doesn’t really provide much insight into their spatial and temporal activity.

Wouldn’t it be fascinating to see what plants male mosquitoes are visiting? They don’t need blood but are they likely to seek out “plant juices”. Could male mosquitoes play a role in plant pollination? I’d love to know how male mosquitoes interact with the local environment. From some of our previous research with Culex molestus, we know that the diet of male mosquitoes can influence the fecundity of the females so perhaps understanding the activity of male mosquitoes could provide some novel control options?

Where to now?

Lots of ideas to consider once the technology is available. However, it is important that we don’t fall into the trap of repeating experiments and reexamining known behaviours just because we have some new technology. What excites me to most is the prospect of answering some questions we don’t actually know how to answer with current technologies. Watch this space!

The photo at the top this post is taken from the CSIRO media release.

6th International Congress of the Society for Vector Ecology

Culex_molestus_Photo_StephenDoggettThis month, medical entomologists from across the globe will come together in California for the 6th International Congress of the Society for Vector Ecology. With thanks to a travel grant provided by the Bill and Melinda Gates Foundation, two of my (recently completed) PhD students will be attending and presenting work on the role of mosquitoes in urban environments and mosquito-borne disease risk.

The Society for Vector Ecology was established in 1968 to bring together individuals interested in the management of vector-borne disease. This includes professionals mostly involved in mosquito research, mosquito control and surveillance operations and communications. Every four years, the society holds a congress either in North America or Europe. The couple of congresses that I’ve attended have been fantastic and I’m greatly disappointed not to be able to attend this year’s meeting.

The 6th International Congress of the Society for Vector Ecology is being held 22-27 September in La Quinta, California, USA. You can have a look at a PDF of the program here.

Although I won’t be able to make it, two of my PhD students will be attending after being awarded travel grants by Bill and Melinda Gates Foundation. They will be presenting some of the work they completed as part of their PhD candidature.

The titles and abstracts of their presentations are below.

Understanding the ecological importance of mosquitoes to insectivorous bats and the implications for mosquito-borne disease management in coastal Australia

Leroy Gonsalves, Bradley Law, Cameron Webb, Vaughan Monamy and Brian Bicknell

Manangement of mosquito-borne disease risk in coastal Australia faces many challenges. Urbanisation is increasing the size and proximity of the community to productive mosquito habitats. Coastal wetlands are also the focus of conservation and rehabilitation efforts. Mosquitoes associated with these wetlands, in particular the saltmarsh mosquito, Aedes vigilax, are abundant, widely dispersing and key vectors of Ross River and Barmah Forest viruses. These mosquitoes may also represent an abundant prey resource for threatened and endangered insectivorous bat species and local authorities are reluctant to approve broadscale mosquito control programs due to concerns regarding indirect impacts on local bat populations. A combination of diet analysis, radio-tracking and prey abundance studies were undertaken. Analysing prey DNA within guano collected from 52 individuals representing five local bat species demonstrated that bats consumed a diverse range of prey dominated by lepidopterans. Consumption of Ae. vigilax was restricted to two species, Vespadelus pumilus and V. vulturnus. Radiotracking of 13 V. vulturnus individuals during periods of relatively large and small population abundances of Ae. vigilax, together with monitoring of prey abundance, revealed that foraging ranges of bats shifted in response to mosquito abundance (and no other prey). These findings suggest that there are species-specific relationships between bats and mosquitoes and that there may be site-specific strategies required to balance mosquito management and bat conservation.

The biology, distribution and genetics of Culex molestus in Australia?

Nur Faeza A Kassim, Cameron E Webb & Richard C Russell

The Culex pipiens subgroup of mosquitoes includes some of the most important vector species involved in mosquito-borne disease transmission internationally and four species within this subgroup are found in Australia. One of these species, Culex molestus, is thought to have been introduced into Australia in the 1940s. Closely associated with subterranean urban habitats, this mosquito has the potential to cause serious nuisance biting impacts but also may cause significant public health risks through the transmission of endemic arboviruses. Exotic pathogens, such as West Nile virus, may also pose a potential threat to biosecurity of Australia. Our review of the literature has confirmed that the current Australian distribution of Cx. molestus is limited to areas south of latitude -28.17ºS. However, given that the mosquito is established in habitats south of the corresponding zone in the northern hemisphere, there is potential for Cx. molestus to spread north into QLD and NT. Molecular analysis of the mosquito indicated that Australian Cx. molestus shared stronger genetic similarity with specimens from Asia than specimens from Europe or North America. Laboratory and field studies have shown that the mosquito is uniquely adapted to urban environments through the expression of autogeny (ability to lay their first batch of eggs without a blood meal) and stenogamy (ability to mate in confined spaces). Culex molestus is active throughout the year and the current trend towards increased water storage in urban areas of Australia has raised concerns of increased nuisance-biting and public health risks in the future. However, the results of our studies indicate that there may be biological and ecological barriers that may lessen the importance of this mosquito in urban mosquito-borne disease cycles. A delay in blood feeding resulting from their obligatory autogeny, combined with limited access to potential reservoir hosts, may reduce the likelihood of them playing a significant role in pathogen transmission.

The London (down) underground mosquito

Culex_molestus_Photo_StephenDoggettOur latest publication in the Australian Journal of Entomology marks the end of a three year research project investigating the biology of a unique introduced mosquito species, Culex molestus, in Australia.

We generally think of nuisance-biting mosquito problems being confined to tropical regions, or at least warm summer conditions. Well, imagine you’re in London in late September 1940. You’re taking shelter in the underground during The Blitz. It is crowded and cold. You’re bitten by mosquitoes too. You’re being bitten by Culex molestus. It is often commonly referred to as the London Underground mosquito and has already been the subject of some fascinating research that has shown how the mosquito has adapted to life within the London underground.

Culex molestus was first described from Egypt in 1775. The mosquito is unique in that it is closely associated with subterranean habitats across the temperate regions of the world, from underground train networks to flooded basements to septic tanks. The species has adapted to these habitats by gaining the ability to mate without the need to swarm (a phenomenon known as stenogamy) and by dropping the requirement of a blood meal to develop the first batch of eggs (a phenomenon known as autogeny). You can read about our previously published work on this here.

Londoners take refuge in the Underground during the Blitz. Taken from “The Tube 150 Anniversary: London Underground, Its Life In Pictures ” Huffington Post UK

The Culex pipiens subgroup of mosquitoes includes a number of globally important vectors of disease-causing pathogens but there are distinct genetic and biological differences between these species that influence their role in transmission cycles. There are four member of the Cx. pipiens subgroup in Australia, Culex australicus, Culex globocoxitus, Culex quinquefasciatus and Culex molestus.

The last of these species, Cx. molestus, had not been the focus of substantial research for over 50 years until a research project by the Department of Medical Entomology and University of Sydney commenced in 2010. The project was designed to address the gaps in our knowledge of these species with a view to assisting in the assessment and management of disease risk associated with this species.

This work was primarily undertaken by Nur Faeza Abu Kassim as part of her PhD candidature with generous support from Ministry of Higher Education Malaysia and Universiti Sains Malaysia.

How did the mosquito get to Australia?

The most cited theory to explain the introduction of Cx. molestus into Australia is that it was through military movements into Melbourne during World War II. This was based on an absence of this species in Victoria during the pre-WWII period. Our research supported this theory.

There were no reports of this species in Australia prior to the 1940s. A review of distribution records for this species confirmed the presence of the species at over 230 locations confirmed that the mosquito has spread throughout the southern parts of Australia and in coastal regions as far north as Tweed Heads (NSW) and Geraldton (WA). No specimens have been reported from Queensland or Northern Territory.

Molecular analysis of specimens collected from throughout Australia, with reference to specimens from Asia, North America and Europe, indicated that Australian Cx. molestus shared the strongest genetic similarity with specimens from Asia. Perhaps the mosquito hitched a ride from Japan into the Pacific and then, with US military, in Australia?

IMG_0170

An example of subterranean habitats closely associated with the presence of Culex molestus

Buzzing (and biting) about all year long?

One of the interesting findings of our research was that the mosquito was active throughout the winter months around Sydney. Analysis of weekly trapping over a 13 month period indicated that the species does not display diapause. As well as generally being a cool-temperate climate mosquito species, perhaps the subterranean habitats provided a little “insulation” from the cold, keeping water temperatures just a little warmer than above ground pools and ponds?

Most of the other nuisance-biting pests disappear during the cooler months. There will occasionally be a few about, particularly during warmer winter days. However, for most local pest mosquitoes, it seems to be the minimum daily temperatures that drive mosquito activity more than maximum daily temperatures. In the case of Cx. molestus, they soldier on regardless.

What about the public health risks?

One of the last unanswered questions regarding the potential public health impacts of Cx. molestus is in relation to the ability of this mosquito to spread local and/or exotic viruses. While local viruses (e.g. Ross River virus) have been isolated from field collected specimens, there is yet to be a thorough investigation of the ability of this species to transmit endemic pathogens such as Murray Valley encephalitis virus or Kunjin virus.

I was involved in a research project assessing the risks posed in eastern Australia due to potential introduction of West Nile virus. Laboratory investigations and field collections provided some valuable information but, due to prevailing environmental conditions at the time, there were very few Cx. molestus collected during the study. We need to complete some of this work to gain a better understanding on how important a role Cx. molestus may play in local disease risk.

One of the key implications of our research is that it highlights the need for urban planners and engineers to consider the risks posed by above and below ground water storage for creating mosquito habitats. While much of my work previously has concentrated on the creation of wetlands and rehabilitation of other habitats in association with urban development, rainwater and storm water storage structures should be adequately designed to reduce mosquito risk.

The full reference for our most recent paper is below:

Kassim NFA, Webb CE and Russell RC (2013) Australian distribution, genetic status and seasonal abundance of the exotic mosquito Culex molestus Forskal (Diptera: Culicidae). Australian Journal of Entomology 52: 185-198 [online]

ABSTRACT. Culex molestus was probably introduced into Australia in the 1940s and represents a potentially important nuisance-biting pest and vector of disease-causing pathogens in urban areas. The aims of this study were to review the literature to determine the current and historical distribution of Cx. molestus in Australia, analyse the genetic similarity of specimens collected from various locations in Australia with reference to specimens from North America, Asia and Europe, and document the seasonal abundance of this mosquito in the Sydney region. Results showed that Cx. molestus is common in southern Australia, but there was no evidence that this mosquito is found north of latitude 28.17°S. Molecular analysis indicated that specimens from various locations throughout Australia shared strong genetic similarity and that it was most likely introduced from Asia, possibly through multiple introductions over the past 70 years. Analysis of the seasonal abundance of Cx. molestus indicated that the species does not display diapause during the cooler months. Consideration should be given to the unique biology and ecology of this species when assessing the public health risk and the surveillance methods required in the management of Cx. molestus within urban areas of Australia.

You can read a media release from the University of Sydney here. Our research was picked up by the local and international media in the past week or so too. You can read about our work in the Daily Telegraph, Newcastle Herald and Sydney Morning Herald.

Previous publications as part of this research project include:

Kassim NFA, Webb C.E. and Russell RC (2012) The importance of males: larval diet and adult sugar-feeding influence reproduction in the mosquito Culex molestus. Journal of the American Mosquito Control Association 28: 312–316

Kassim NFA, Webb C.E. and Russell RC (2012) Is the expression of autogeny by Culex molestus Forskal (Diptera: Culicidae) influenced by larval nutrition or by adult mating, sugar feeding or blood feeding? Journal of Vector Ecology 37: 162–171

Kassim NFA, Webb C.E. and Russell RC (2012) Culex molestus Forskal (Diptera: Culicidae) in Australia: colonisation, stenogamy, autogeny, oviposition and larval development. Australian Journal of Entomology 51: 67-77

Does male diet influence mosquito reproduction?

My latest publication has appeared in the Journal of the American Mosquito Control Association in December 2012. This paper reports on some biological experiments conducted by my PhD student Nur Abu Kassim. She was interested in investigating the role of diet (including how much food immature stages ate and if adult mosquitoes had access to sugar) on male mosquitoes and the resulting egg development by females.

Nur conducted her experiments using Culex molestus, this species is a member of the Culex pipiens group. This group of mosquitoes is important internationally as it contains species closely associated with the transmission of disease-causing pathogens, in particular West Nile virus. Culex molestus is an interesting species in that it can develop its first batch of eggs without a blood meal. You can read about our earlier studies here and here.

The results indicated that diet of male mosquitoes, both access to food in immature stages and access to sugar as adults, influenced the number of autogenous eggs and hatching rates of those eggs.

Here is the abstract:

Culex molestus is an obligatory autogenous mosquito that is closely associated with subterranean habitats in urban areas. The objective of our study was to investigate the influence of larval and adult nutrition on the role of males in determining the expression of autogeny in Cx. molestus. Mosquitoes raised at low and high larval diets had sex ratio, wing length, mating rates, autogenous egg raft size, and hatching rates recorded. There was a higher ratio of males to females when raised at a low larval diet. Mean wing lengths of both males and females were significantly greater when raised at the high larval diet regime. Regardless of larval or adult diet, males mated with only a single female. Mosquitoes raised at the higher larval diet regimes developed significantly more autogenous eggs. However, the egg raft size was reduced when adult females were denied access to sugar. The results of this study indicate that the performance of males in the reproductive process is influenced by both larval diet and adult sugar feeding.

Full reference:

Kassim NFA, Webb CE & Russell RC. 2012. The Importance of Males: Larval Diet and Adult Sugar Feeding Influences Reproduction in Culex molestus. Journal of the American Mosquito Control Association 28(4):312-316. online