Stowaway mozzies enter Australia from Asian holiday spots – and they’re resistant to insecticides



File 20190320 93051 1rj4pog.jpg?ixlib=rb 1.1
We might not be able to use common insecticides to kill mosquitoes that arrive from other countries.
from www.shutterstock.com

Tom Schmidt, University of Melbourne; Andrew Weeks, University of Melbourne, and Ary Hoffmann, University of Melbourne

Planning a trip to the tropics? You might end up bringing home more than just a tan and a towel.

Our latest research looked at mosquitoes that travel as secret stowaways on flights returning to Australia and New Zealand from popular holiday destinations.

We found mosquito stowaways mostly enter Australia from Southeast Asia, and enter New Zealand from the Pacific Islands. Worse still, most of these stowaways are resistant to a wide range of insecticides, and could spread disease and be difficult to control in their new homes.




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Secret stowaways

Undetected insects and other small creatures are transported by accident when people travel, and can cause enormous damage when they invade new locations.

Of all stowaway species, few have been as destructive as mosquitoes. Over the past 500 years, mosquitoes such as the yellow fever mosquito (Aedes aegypti) and Asian tiger mosquito (Aedes albopictus) have spread throughout the world’s tropical and subtropical regions.

Dengue spread by Aedes aegypti mosquitoes now affects tens to hundreds of millions of people every year.




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Mosquitoes first travelled onboard wooden sailing ships, and now move atop container ships and within aircraft.

Adults in your luggage

You probably won’t see Aedes mosquitoes buzzing about the cabin on your next inbound flight from the tropics. They are usually transported with cargo, either as adults or occasionally as eggs (that can hatch once in contact with water).

It only takes a few Aedes stowaways to start a new invasion. In Australia, they’ve been caught at international airports and seaports, and in recent years there has been a large increase in detections.

Aedes aegypti mosquito detections per year at Australian international terminals – passenger airline terminals in white; seaports or freight terminals in black.
Tom Schmidt, Author provided



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In our new paper, we set out to determine where stowaway Aedes aegypti collected in Australia and New Zealand were coming from. This hasn’t previously been possible.

Usually, mosquitoes are only collected after they have “disembarked” from their boat or plane. Government authorities monitor these stowaways by setting traps around airports or seaports that can capture adult mosquitoes. Using this method alone, they’re not able to tell which plane they came on.

But our approach added another layer: we looked at the DNA of collected mosquitoes. We knew from our previous work that the DNA from any two mosquitoes from the same location (such as Vietnam, for example) would be more similar than the DNA from two mosquitoes from different locations (such as Vietnam and Brazil).

So we built a DNA reference databank of Aedes aegypti collected from around the world, and compared the DNA of the Aedes aegypti stowaways to this reference databank. We could then work out whether a stowaway mosquito came from a particular location.

We identified the country of origin of most of the Aedes aegypti stowaways. The majority of these mosquitoes detected in Australia are likely to have come from flights originating in Bali.

Here’s where the Aedes aegypti mozzies come into Australia and New Zealand from.
Tom Schmidt, Author provided

Now we can work with these countries to build smarter systems for stopping the movement of stowaways.

As the project continues, we will keep adding new collections of Aedes aegypti to our reference databank. This will make it easier to identify the origin of future stowaways.

New mosquitoes are a problem

As Aedes aegypti has existed in Australia since the 19th century, the value of this research may seem hard to grasp. Why worry about invasions by a species that’s already here? There are two key reasons.

Currently, Aedes aegypti is only found in northern Australia. It is not found in any of Australia’s capital cities where the majority of Australians live. If Aedes aegypti established a population in a capital city, such as Brisbane, there would be more chance of the dengue virus being spread in Australia.

The other key reason is because of insecticide resistance. In places where people use lots of insecticide to control Aedes aegypti, the mosquitoes develop resistance to these chemicals. This resistance generally comes from one or more DNA mutations, which are passed from parents to their offspring.




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Importantly, none of these mutations are currently found in Australian Aedes aegpyti. The danger is that mosquitoes from overseas could introduce these resistance mutations into Australian Aedes aegpyti populations. This would make it harder to control them with insecticides if there is a dengue outbreak in the future.

In our study, we found that every Aedes aegpyti stowaway that had come from overseas had at least one insecticide resistance mutation. Most mosquitoes had multiple mutations, which should make them resistant to multiple types of insecticides. Ironically, these include the same types of insecticides used on planes to stop the movement of stowaways.

Other species to watch

We can now start tracking other stowaway species using the same methods. The Asian tiger mosquito (Aedes albopictus) hasn’t been found on mainland Australia, but has invaded the Torres Strait Islands and may reach the Cape York Peninsula soon.

Worse still, it is even better than Aedes aegypti at stowing away, as Aedes albopictus eggs can handle a wider range of temperatures.

A future invasion of Aedes albopictus could take place through an airport or seaport in any major Australian city. Although it is not as effective as Aedes aegypti at spreading dengue, this mosquito is aggressive and has a painful bite. This has given it the nickname “the barbecue stopper”.

Beyond mosquitoes, our DNA-based approach can also be applied to other pests. This should be particularly important for protecting Australia’s A$45 billion dollar agricultural export market as international movement of people and goods continues to increase.




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Explainer: what is Murray Valley encephalitis virus?


The Conversation


Tom Schmidt, Research fellow, University of Melbourne; Andrew Weeks, Senior Research Fellow, University of Melbourne, and Ary Hoffmann, Professor, School of BioSciences and Bio21 Institute, University of Melbourne

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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Explainer: what is Murray Valley encephalitis virus?


Ana Ramírez, James Cook University; Andrew Francis van den Hurk, The University of Queensland; Cameron Webb, University of Sydney, and Scott Ritchie, James Cook University

Western Australian health authorities recently issued warnings about Murray Valley encephalitis, a serious disease that can spread by the bite of an infected mosquito and cause inflammation of the brain.

Thankfully, no human cases have been reported this wet season. The virus that causes the disease was detected in chickens in the Kimberley region. These “sentinel chickens” act as an early warning system for potential disease outbreaks.

What is Murray Valley encephalitis virus?

Murray Valley encephalitis virus is named after the Murray Valley in southeastern Australia. The virus was first isolated from patients who died from encephalitis during an outbreak there in 1951.

The virus is a member of the Flavivirus family and is closely related to Japanese encephalitis virus, a major cause of encephalitis in Asia.

Murray Valley encephalitis virus is found in northern Australia circulating between mosquitoes, especially Culex annulirostris, and water birds. Occasionally the virus spreads to southern regions, as mosquitoes come into contact with infected birds that have migrated from northern regions.




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How serious is the illness?

After being transmitted by an infected mosquito, the virus incubates for around two weeks.

Most people infected don’t develop symptoms. But, if you’re unlucky, you could develop symptoms ranging from fever and headache to paralysis, encephalitis and coma.

Around 40% of people who develop symptoms won’t fully recover and about 25% die. Generally, one or two human cases are reported in Australia per year.

Since the 1950s, there have been sporadic outbreaks of Murray Valley encephalitis, most notably in 1974 and 2011. The 1974 outbreak was Australia-wide, resulting in 58 cases and 12 deaths.

It’s likely the virus has been causing disease since at least the early 1900s when epidemics of encephalitis were attributed to a mysterious illness called Australian X disease.

Traditional monitoring of mosquito-borne diseases relies on the collection of mosquitoes using specially designed traps baited with carbon dioxide.
Cameron Webb

Early warning system

Given the severity of Murray Valley encephalitis, health authorities rely on early warning systems to guide their responses.

One of the most valuable surveillance tools to date have been chooks because the virus circulates between birds and mosquitoes. Flocks of chickens are placed in areas with past evidence of virus circulation and where mosquitoes are buzzing about.

Chickens are highly susceptible to infection so blood samples are routinely taken and analysed to determine evidence of virus infection. If a chicken tests positive, the virus has been active in an area.

The good news is that even if the chickens have been bitten, they don’t get sick.

Mosquitoes can also be collected in the field using a variety of traps. Captured mosquitoes are counted, grouped by species and tested to see if they’re carrying the virus.

This method is very sensitive: it can identify as little as one infected mosquito in a group of 1,000. But processing is labour-intensive.




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How can technology help track the virus?

Novel approaches are allowing scientists to more effectively detect viruses in mosquito populations.

Mosquitoes feed on more than just blood. They also need a sugar fix from time to time, usually plant nectar. When they feed on sugary substances, they eject small amounts of virus in their saliva.

This led researchers to develop traps that contain special cards coated in honey. When the mosquitoes feed on the cards, they spit out virus, which specific tests can then detect.

We are also investigating whether mosquito poo could be used to enhance the sugar-based surveillance system. Mosquitoes spit only tiny amounts of virus, whereas they poo a lot (300 times more than they spit).

This mosquito poo can contain a treasure trove of genetic material, including viruses. But we’re still working out the best way to collect the poo.

Mosquito poo, shown here after mosquitoes have fed on coloured honey, can be used to detect viruses like Murray Valley encephalitis.
Dagmar Meyer

Staying safe from Murray Valley encephalitis

There is no vaccine or specific treatment for the virus. Avoiding mosquito bites is the only way to protect yourself from the virus. You can do this by:

  • wearing protective clothing when outdoors

  • avoiding being outdoors when the mosquitoes that transmit the virus are most active (dawn and dusk)

  • using repellents, mosquito coils, insect screens and mosquito nets

  • following public health advisories for your area.

The virus is very rare and your chances of contracting the disease are extremely low, but not being bitten is the best defence.The Conversation

Ana Ramírez, PhD candidate, James Cook University; Andrew Francis van den Hurk, Medical Entomologist, The University of Queensland; Cameron Webb, Clinical Lecturer and Principal Hospital Scientist, University of Sydney, and Scott Ritchie, Professorial Research Fellow, James Cook University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Why naming all our mozzies is important for fighting disease


File 20180223 108139 lvidlr.jpg?ixlib=rb 1.1
And you can be…Susan.
from http://www.shutterstock.com

Bryan Lessard, CSIRO

Notorious for spreading diseases like malaria and Zika virus overseas, mosquitoes contribute to thousands of cases of human disease in Australia each year. But only half of Australia’s approximately 400 different species of mosquitoes have been scientifically named and described. So how are scientists able to tell the unnamed species apart?

Climate change means population change

Mosquito populations and our ability to predict disease outbreaks are likely to change in the future. As climates change, disease-carrying mozzies who love the heat may spread further south into populated cities.

As human populations continue to grow in Australia, they will interact with different communities of wild animals that act as disease reservoirs, as well as different mosquito species that may be capable of carrying these diseases. The expansion of agricultural and urban water storages will also create new homes for mosquito larvae to mature, allowing mosquitoes to spread further throughout the country.




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Mosquito larvae need a body of water to mature in.
James Gathany, CDC

Agents of disease

Mosquitoes like the native Common Banded Mosquito (Culex annulirostris) are known to spread human diseases such as Ross River virus, Barmah Forest virus, Dengue fever and Murray Valley encephalitis.

It’s not the adult mosquito itself that causes the disease, but the viruses and other microbes that accumulate in the mosquito’s saliva and are injected into the bloodstream of the unsuspecting victim during feeding.

The mosquitoes that bite humans are female, requiring the proteins in blood to ripen their eggs and reach sexual maturity. Male mosquitoes, and females of some species, are completely vegetarian, opting to drink nectar from flowers, and are useful pollinators.

The life cycle of a mosquito.
from http://www.shutterstock.com



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The name game

Mosquitoes belong to the fly family Culicidae and are an important part of our biodiversity. There are more than 3,680 known species of mosquitoes in the world. Taxonomists, scientists who classify organisms, have been able to formally name more than 230 species in Australia.

The classification of Australian mosquitoes tapered off in the 1980s with the publication of the last volume of The Culicidae of the Australasian Region and passing of Dr Elizabeth Marks who was the most important contributor to our understanding of Australian mosquitoes.

She left behind 171 unique species with code numbers like “Culex sp No. 32”, but unfortunately these new species were never formally described and remained unnamed after her death. This isn’t uncommon in biodiversity research, as biologists estimate that we’ve only named 25% of life on earth during a time when there is an alarming decline in the taxonomic workforce.

Dr Marks’ unnamed species are still held in Australian entomology collections, like CSIRO’s Australian National Insect Collection, Museum Victoria and the Queensland Museum. Although all the major disease-carrying species of mosquitoes are known in the world, several of Marks’ undescribed Australian species are blood feeding and may have the capacity to transmit diseases.

How do we tell mozzies apart?

Naming, describing and establishing the correct classification of Australia’s mosquitoes is the first step to understanding their role in disease transmission. This is difficult work as adults are small and fragile, and important diagnostic features that are used to tell species apart, like antennae, legs and even tiny scales, are easily lost or damaged.

CSIRO scientists, with support from the Australian Biological Resources Study, Government of Western Australia Department of Health, and University of Queensland, have been tasked with naming Australia’s undescribed mosquitoes. New species will be named and described based on the appearance of the adults and infant larval stages which are commonly intercepted by mozzie surveillance officers. New identification tools will also be created so others can quickly and reliably identify the Australian species.

A 100 year old specimen of the native Common Banded Mosquito Culex annulirostris, capable of spreading Murray Valley encephalitis virus, one of 12 million specimens held in CSIRO’s Australian National Insect Collection in Canberra.
CSIRO/Dr Bryan Lessard



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Scientists are now able to extract DNA and sequence the entire mitochondrial genome from very old museum specimens. CSIRO are using these next generation techniques to generate a reliable DNA reference database of Australian mosquitoes to be used by other researchers and mozzie surveillance officers to accurately identify specimens and diagnose new species. CSIRO are also digitising museum specimens to unlock distribution data and establish the geographical boundaries for the Australian species.

By naming and describing new species, we will gain a more complete picture of our mosquito fauna, and its role in disease transmission. This will make us better prepared to manage our mosquitoes and human health in the future as the climate changes and our growing human population moves into new areas of Australia.The Conversation

Bryan Lessard, Postdoctoral Research Fellow, CSIRO

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Mozzie repellent clothing might stop some bites but you’ll still need a cream or spray



File 20181121 161638 1vc338a.jpg?ixlib=rb 1.1
Clothes can offer some protection.
John Jones/Flickr, CC BY

Cameron Webb, University of Sydney

A range of shirts, pants, socks and accessories sold in specialist camping and fishing retailers claim to protect against mosquito bites for various periods.

In regions experiencing a high risk of mosquito-borne disease, insecticide treated school uniforms have been used to help provide extra protection for students.

During the 2016 outbreak of Zika virus in South America, some countries issued insecticide-treated uniforms to athletes travelling to the Olympic Games.

Some academics have even suggested fashion designers be encouraged to design attractive and innovative “mosquito-proof” clothing.




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But while the technology has promise, commercially available mosquito-repellent clothing isn’t the answer to all our mozzie problems.

Some items of clothing might offer some protection from mosquito bites, but it’s unclear if they offer enough protection to reduce the risk of disease. And you’ll still need to use repellent on those uncovered body parts.

First came mosquito-proof beds

Bed nets have been used to create a barrier between people and biting mosquitoes for centuries. This was long before we discovered mosquitoes transmitted pathogens that cause fatal and debilitating diseases such as malaria. Preventing nuisance-biting and buzzing was reason alone to sleep under netting.

Bed nets have turned out to be a valuable tool in reducing malaria in many parts of the world. And they offer better protection if you add insecticides.

The insecticide of choice is usually permethrin. This and other closely related synthetic pyrethroids are commonly used for pest control and have been assessed as safe for use by the United States Environmental Protection Authority, the Australian Pesticides and Veterinary Medicines Authority and other regulatory bodies.




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New technologies have also allowed for the development of long-lasting insecticidal bed nets, offering extended protection against mosquito bites, perhaps up to three years, even with repeated washing.

Mosquito repellent clothing

Innovations in clothing that prevent insect bites have primarily come from the United States military. Mosquito-borne disease is a major concern for military around the globe. Much research funding has been invested in strategies to provide the best protection for personnel.

Traditional insect repellents, such as DEET or picaridin, are applied to the skin to prevent mosquitoes from landing and biting.

While permethrin will repel some mosquitoes, treated clothing most effectively works by killing the mosquitoes landing and trying to bite through the fabric.

Clothing treated with permethrin has been shown to protect against mosquitoes and ticks, as well as other biting insects and mites. For these studies, clothing was generally soaked in solutions or sprayed with insecticides to ensure adequate protection.

Clothing made from insecticide impregnated fabrics may help reduce mosquito bites.
Cameron Webb (NSW Health Pathology)

Fabrics factory-treated with insecticides, as used by many military forces, are purported to provide more effective protection. But while some studies suggest clothing made from these fabrics provide protection even after multiple washes, others suggest the “factory-treated” fabrics don’t provide greater levels of protection than “do it yourself” versions.

Overall, the current evidence suggests insecticide-treated clothing may reduce the number of mosquito bites you get, but it doesn’t offer full protection.

More research is needed to determine if insecticide-treated clothing can prevent or reduce rates of mosquito-borne disease.

Better labelling and regulation

All products that claim to provide protection from insect bites must be registered with the Australian Pesticides and Veterinary Medicines Authority. This includes sprays, creams and roll-on formulations of repellents.

Anything labelled as “insect repelling”, including insecticide treated clothing, requires registration. Clothing marketed as simply “protective” (such as hats with netting) doesn’t. This approach reflects the requirements of the US EPA.




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If you’re shopping for insect-repellent clothing, check the label to see if it states that it is registered by the APVMA. You should see a registration number and the insecticide used in the fabric clearly displayed on the clothing’s tag.

While some products will be registered, there are still some concerns about how the efficacy of mosquito bite protection is assessed.

There is likely to be growing demand for these types of products and experts are calling for internationally accepted guidelines to test these products. Similar guidelines exist for topical repellents.

Finally, keep in mind that while various forms of insecticide-treated clothing will help reduce the number of mosquito bites, they won’t provide a halo of bite-free protection around your whole body.

Remember to apply a topical insect repellent to exposed areas of skin, such as hands and face, to ensure you’re adequately protected from mosquito bites.The Conversation

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

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Will the arrival of El Niño mean fewer mosquitoes this summer?



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A hot summer will mean wetlands dry out faster than ever, so how will pest mosquitoes respond?
Cameron Webb (NSW Health Pathology), Author provided

Cameron Webb, University of Sydney

Once the warm weather arrives, you know mosquitoes won’t be far behind. Spring heatwaves associated with the impending arrival of El Niño to the east coast of Australia may mean we’ll get an early taste of summer, but what about mosquitoes? Does a long, hot summer mean fewer annoying buzzing and biting beasts bothering us whenever we spend time outdoors?

Where do mosquitoes come from?

Mosquitoes are complex animals. Like all insects, they thrive in warm weather, but they need more than just heat, they need water.

Mosquitoes lay their eggs on or around water. Without it, they cannot complete their life cycle. Mosquito “wrigglers” hatch out from eggs and spend a week or so swimming about before emerging and flying off in search of blood. Depending on where the water is, whether it is wetlands, puddles or water-filled containers, different kinds of mosquitoes will be present.

There are hundreds of different mosquitoes in Australia. Some like salty water, some like fresh. Some need pristine conditions while some will tolerate filthy water trapped at the bottom of a septic tank.

Because mosquitoes rely on water, rainfall plays a critical role in determining how many mosquitoes will be buzzing about this summer.




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A hot, dry summer must mean fewer mosquitoes?

The likelihood that an El Niño will bring drier and warmer conditions to eastern Australia this summer is increasing. The latest predictions from the Bureau of Meteorology are that there is a 70% chance an El Nino will occur this year, about three times more than usual.

At first, this may seem like good news for those averse to mosquito bites, but don’t pack away the repellent just yet.

While floods bring mosquitoes, and often outbreaks of mosquito-borne disease, drought will knock out almost all mosquitoes. It is true that the ongoing dry conditions across inland areas of Australia will ensure mosquito populations remain low, but that doesn’t mean mosquitoes will disappear completely.




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Water doesn’t just come from rain

While a lack of rain will keep many wetlands dry, that isn’t the case for our coastal wetlands. Some of the worst pest mosquitoes in Australia are found in our mangroves, saltmarshes and sedgelands.

Mosquitoes, like the saltmarsh mosquito, Aedes vigilax, love wetlands regularly flooded by high tides. The eggs of this mosquito, laid in moist wetland mud, survive long periods of dry conditions. Once covered by tides, these hatch, complete development within a week, and emerge in extraordinary numbers to fly kilometres away into nearby communities to bite and spread disease-causing pathogens such as Ross River virus.

Not only have these mosquitoes found a way to survive without rain, they thrive in hot and dry conditions. Without substantial rainfall, the pools and ponds in the wetlands dry completely, killing off any fish or other aquatic predators, ensuring perfect conditions once the next series of tides comes flooding in. The arrival of El Niño may be bad news for lots of wetland wildlife, but it isn’t all bad news for mosquitoes.

The saltmarsh mosquito, Aedes vigilax, is one of the most important pest mosquitoes in coastal regions of Australia and has adapted to thrive in hot and dry conditions.
Stephen Doggett (NSW Health Pathology)

Bringing mosquitoes home

Much has been made of the impact of heatwaves on human health. It may also inadvertently increase health risks in metropolitan regions of Australia. A shortage of water increases the need to conserve and store water around the backyard. Unfortunately, that also means creating a home for mosquitoes.

One of the most widespread mosquitoes in the country, a mosquito that has probably bitten almost every Australian, is the backyard mosquito Aedes notoscriptus. This mosquito is found in water-filled containers around the backyard, from drains and roof gutters to rainwater tanks and bird baths. While you’d think hot and dry conditions will impact this mosquito, think about the extra effort we’re taking to store water around the home. If your rainwater tank isn’t properly screened or you’re keeping uncovered bins and buckets around the backyard filled with water, you’ll be providing a home for mosquitoes.

The debate about the impact of a changing climate on mosquitoes and mosquito-borne disease often focuses on the spread of tropical diseases into warming temperate regions. The truth is it may be the way humans respond to a changing climate through water-saving measures around the home that could increase mosquito impacts in urban areas. This also may bring a risk of exotic mosquitoes to our suburbs, which could transmit more serious mosquito-borne pathogens such as dengue, chikungunya and Zika viruses.

While some parts of Australia will have fewer annoying mozzies this summer, don’t be complacent about taking steps to avoid mosquito bites. Choose and use the right insect repellents and reduce opportunities for mosquitoes to move into your backyard by covering up water-holding containers.The Conversation

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

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Microplastics are getting into mosquitoes and contaminating new food chains



File 20180918 158240 1dtiepp.jpg?ixlib=rb 1.1

khlungcenter/Shutterstock

Amanda Callaghan, University of Reading and Rana Al-jaibachi, University of Reading

There is no doubt that plastic pollution in oceans is a growing worldwide problem. The internet is full of images of seabirds and other marine animals entangled in plastic waste, and animals starve because their guts are blocked with plastic bags.

But the problem goes much deeper than this. Much plastic pollution is in the form of microplastics, tiny fragments less than five micrometres in size and invisible to the naked eye. Our new research shows that these microplastics are even getting into tiny flying insects such as mosquitoes. And this means the plastic can eventually contaminate animals in a more unlikely environment: the air.

Microplastics can come from larger plastic items as they break down, but are also released directly into waste water in their millions in the form of tiny beads found in many cosmetic products including face wash and toothpaste (though these are now banned in many countries). Many tiny animals can’t tell the difference between their food and microplastics so end up eating them. Once inside an animal, the plastic can transfer via the food chain into fish and other creatures and eventually become a potential health problem for humans.

Mosquitoes leave the water and take microplastics with them.
Shaun Wilkinson/Shutterstock

By studying mosquitoes, we have found a previously unknown way for plastic to pollute the environment and contaminate the food chain. Our new paper, published in Biology Letters, shows for the first time that microplastics can be kept inside a water-dwelling animal as they grow from one life stage to another.

Although most microplastic research has focused on the sea, plastic pollution is also a serious problem in freshwater, including rivers and lakes. Much of the freshwater research has concentrated on animals that live in the water throughout their life. But freshwater insects such as mosquitoes start their lives (as eggs) in water and, after several stages, eventually fly away when they grow up.

Testing the mosquitoes

It occurred to us that aquatic insects might carry plastics out of the water if they were able to keep the plastics in their body through their development. We tested this possibility by feeding microplastics to mosquito larvae in a laboratory setting. We fed the aquatic young in their third larvae stage food with or without microplastic beads.

We then took samples of the animals when the larvae shed their skin to become larger fourth-stage larvae, when they transformed into a non-feeding stage called a pupa, and when they emerged from the water as a flying adult. We found the beads in all the life stages, although the numbers went down as the animals developed.

Plastics were retained as the mosquitoes went through different life stages.
Blue Ring Media/Shutterstock

We were able to locate and count the microplastic beads because they were fluorescent. We found beads in the gut and in the mosquito version of the kidney, an organ that we know survives the development process intact. This shows that not only do aquatic insects such as mosquitoes eat both sizes of microplastics, they can keep them in their gut and kidney as they develop from a feeding juvenile larva up to a flying adult.

In this way, any flying insect that spends part of its life in water can become a carrier of plastic pollution. And flying insects are eaten in their thousands by predatory insects in the air such as dragonflies as well as by birds and bats.

Our results have important implications since any aquatic insect that can eat microplastics in the water could potentially carry them in their body to their flying stage where they can move the plastics into new food chains. As a result, freshwater plastic pollution is a problem that has implications far beyond those of water quality and eventual marine pollution.

Clearly these results raise a number of questions, including what effect microplastics have on the survival and development of mosquitoes through their life stages. And we still need to examine the effect of different types and sizes of plastics on more species to see how widespread an issue this could become.The Conversation

Amanda Callaghan, Associate Professor of Zoology, University of Reading and Rana Al-jaibachi, PhD researcher, University of Reading

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Mozzies are evolving to beat insecticides – except in Australia



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Mosquitoes are the main vectors for dengue and zika. Insecticides are our best weapon against them.
Anja Jonsson/Flickr

Ary Hoffmann, University of Melbourne; Nancy Margaret Endersby-Harshman, University of Melbourne, and Scott Ritchie, James Cook University

Chemical pesticides have been used for many years to control insect populations and remain the most important method of managing diseases carried by pests, including mosquitoes. However, insects have fought back by evolving resistance to many pesticides. There are now thousands of instances of evolved resistance, which make some chemical classes completely ineffective.

The Aedes mosquito, largely responsible for the spread of viruses like dengue and zika, has globally developed resistance to commonly used chemicals, including pyrethroids. Pyrethroids are the most used insecticides in the world, which includes the control of dengue outbreaks and quarantine breaches at air and sea ports.

In Asia and the Americas, pyrethroid resistance in Aedes mosquitoes is now widespread. In Australia, our mosquitoes have not developed these defences and pyrethroids are still very effective.

The difference lies in our stringent and careful protocols for chemical use. As the global community fights zika and other mosquito-borne diseases, there are lessons to be learned from Australia’s success.

Developing resistance

Mosquitoes usually become resistant to pyrethroids through the mutation of a sodium channel gene that controls the movement of ions across cell membranes. Mutations in a single gene are enough to make mosquitoes almost completely resistant to the level of pyrethroids used in insecticides.

The mutations first arises in a population by chance, and are rare. However, they rapidly spread as resistant females breed. The more times a mosquito population is exposed to the same chemical, the more the natural selection process favours their impervious offspring.

Eventually, when many individuals in a population carry the resistance mutation, the chemical becomes ineffective. This can happen where insecticide “fogging” is common practice. Overseas, fogging is sometimes undertaken across entire neighbourhoods, several times a month, despite concerns about its effectiveness as well as its environmental and health impacts.

A pest exterminator carries out insecticide fogging in an apartment block in Singapore.
EPA, Wallace Woon/AAP

Once resistance develops, it can spread to non-resistant mosquito populations in other areas. Pest species, including mosquitoes, are often highly mobile because they fly or are carried passively (in vehicles, ships and planes) at any stage of their life cycle. Their mobility means mutations spread quickly, crossing borders and possibly seas.

We can still control Australian mosquitoes

Despite this, Australian populations of Aedes mosquitoes remain susceptible to pyrethroids. Aedes aegypti (the yellow fever mosquito) is the main disease-carrying mosquito in Australia. Its population is restricted to urban areas of northern Queensland, where dengue can occur.

Recent research found that all Australian populations of this species are still vulnerable to pyrethroids. None of the hundreds of mosquitoes tested had any mutations in the sodium channel gene, despite the high incidence of such mutations in mosquito populations of South-East Asia.

A female Aedes aegypti mosquito during a feed.
James Gathany, CDC Prof Frank Hadley Collins/Wikimedia

We believe these mosquitoes remain vulnerable to pyrethroids because in Australia pressure to select for resistance has been low.

Australia does not carry out routine fogging. If dengue is detected in an area, pyrethoids are used in highly regimented and limited fashion. Spraying is restricted to the insides of premises within selected house blocks, and then only for a short period.

Importantly, water-filled artificial containers, which can serve as a habitat for larvae, are treated with insect growth regulators, which do not select for the pyrethroid resistance mutations.

Exporting resistance

With chemical resistance growing around the world, it is more urgent than ever that we co-ordinate action to control and reduce risk of resistance. Unfortunately, no global guidelines exist to minimise the evolution of resistance in mosquitoes.

Adopting pesticide resistance management strategies has proven to be effective against other pests – for example, the corn earworm (Helicoverpa armigera). Guidelines include rotating different class of pesticides to deny pests the chance to develop resistance, and investing in non-chemical options such as natural predators of target pests.

Resistance management strategies are particularly critical for new pesticides that have different modes of attack, such as preventing juvenile insects from moulting, or attacking various chemical receptors.

The ConversationTo prolong the effectiveness of pesticides, we must develop these strategies before resistance begins to develop. North Queensland may be an example to the rest of the world on the best path forward.

Ary Hoffmann, Professor, School of BioSciences and Bio21 Institute, University of Melbourne; Nancy Margaret Endersby-Harshman, Research fellow, University of Melbourne, and Scott Ritchie, Professorial Research Fellow, James Cook University

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