By Lynley Hargreaves 02/11/2017 18

It’s a familiar New Zealand story, the havoc wrecked by all the pest species we’ve brought in. But in the case of mosquitoes, the worst might be yet to come. There were 12 mostly bird-nibbling mosquito species in pre-European times. Since our arrival, three new species have become permanently established here. We’ve stopped dozens more at our ports, and eradicated one. Climate change will make that border control more difficult, says University of Auckland Senior Research Fellow José Derraik. And if new species arrive, an outbreak of mosquito-borne disease in New Zealand becomes ever more likely.

Dr José Derraik

What’s a worst case scenario of mosquito-borne disease in New Zealand?

If a species such as Aedes albopictus – the Asian tiger mosquito – or Aedes aegypti – known as the yellow fever mosquito – became established here. These are two of the most important mosquito vectors of human disease worldwide. Under the climatic models that have been done in the past, climate change would make Aedes aegypti more likely to become established. However, due to temperature limitations it would probably be restricted to the northern tip of New Zealand. But Aedes albopictus is one of the world’s worst invasive species, and it could establish under our temperate climate. Importantly, it’s an efficient vector of a number of important human pathogens, such as dengue fever viruses or Zika virus, and it can breed in a wide range of microhabitats in close association with humans (e.g. used tyres, buckets, etc). This is a species that would be of major concern, because it would greatly magnify the likelihood of an outbreak occurring in our country. Aedes albopictus is one of the reasons why we need one of the strictest biosecurity controls in the world at our borders.

In the modern world we now have rapid movement of people from one country to another. New Zealand has a constant inflow of arrivals – New Zealanders returning from overseas as well as foreign visitors – and invariably some of these travellers enter the country infected with a virus acquired overseas. If one of these people is then “bitten” by a suitable mosquito vector an outbreak could eventuate. This isn’t a fictitious scenario, as this is exactly what happened with a major outbreak of Ross River Virus in Fiji in 1979. Hardly anyone in New Zealand has been exposed to mosquito-borne viruses, so our population would be highly susceptible to infection, and a disease could spread rather rapidly under the right conditions.

It is important to point out that New Zealand is a very unique place. If one disregards Antarctica, we are the only country in the planet where there has never been a single confirmed case of disease transmission from mosquitoes to humans within national borders.

If this is possible, why hasn’t it happened already?

The key issue is that we don’t have very efficient mosquito vectors established in New Zealand, yet. Things have changed a lot in the past century. If you think about New Zealand before humans arrived, the only land mammals that we had were bats (who happen to eat a lot of mosquitoes). There were only 12 native species of mosquito – that’s a very low number compared to similar-sized temperate countries – and although some will feed on most warm-blooded animal, they had evolved primarily to feed on birds.

When humans came we completely changed New Zealand’s environment: we brought in a lot of land mammals, we wiped most of our forests out, and we accidentally brought in three exotic species of mosquito. Culex quinquefasciatus and Aedes notoscriptus are very good mammalian feeders which could become disease vectors in New Zealand. Aedes notoscriptus in particular, is a very aggressive feeder. It’ll breed in any object that can harbor stagnant water so that is very well established in urban areas around Auckland. Currently, this is probably the mosquito that could most likely lead to an outbreak in New Zealand. It has been shown to play a role in vectoring diseases in Australia. But it’s not a very efficient vector of viruses to humans. This issue, combined with a relatively low level of virus-infected travelers, means this scenario hasn’t played out in New Zealand yet.

Our biosecurity measures have successfully stopped more than 30 other species from establishing in the country by intercepting them at port entry points – including both the Asian tiger mosquito and Aedes aegypti. The southern saltmarsh mosquito Aedes camptorhynchus, which can transmit the Ross River virus, was found in 1998 and became established in certain areas of the North Island. Fortunately, it seems that the species was successfully eradicated in 2010.

How will climate change increase these risks?

When I did my Masters degree in Dunedin, one of my mentors Professor Alan Mark, commented that ideally the main entry port into New Zealand should be Dunedin. If all goods and most of the people arrived in New Zealand down south, we’d have a much lower number of exotic species becoming established here. This is because the colder climate would act as a barrier, and likely prevent many exotic species from getting a foothold here.

Climate change and warmer temperatures will create conditions that are more suitable for important mosquito vectors to become established in New Zealand. With warmer temperatures ‘moving’ southwards, it’s going to make it easier for new species to establish around other ports of entry further south, so that maintaining stringent border controls becomes more complicated and expensive. In addition, because of the temperate climate of New Zealand, mosquito vectors have a relatively narrow window period to reach higher densities, and this would likely be extended with climate change. Further, warmer temperatures would also improve conditions for virus replication and transmission in New Zealand soil. I believe most researchers in this area would say it’s not a matter of “if”, but “when” an outbreak will happen here.

There’s a term “invasional meltdown”, describing how animals like possums actually make this situation worse too. Can you explain that?

Yes, if you think of the scenario of how New Zealand land cover has changed, most of our forests has been replaced by urban areas and farms. Native New Zealand mosquitoes were mostly adapted to live in a forest environment. When I did my PhD, for example, it was very clear that if you went further into the Waitakere Ranges, you would not find a single exotic mosquito species. But when you go to highly modified environments there is marked a shift towards exotic species.

So, possums, cattle, and humans favour exotic mosquitoes as sources of mammalian blood, which is generally preferred by mosquito vectors that could establish in New Zealand. Further, animals such as possums have a marked environmental impact, and if left unchecked they could also aid exotic mosquito invaders through the degradation of our forest habitats. In some cases, these introduced mammals could also act as reservoir hosts for human pathogens. Possums, for example, are potential hosts of Ross River virus.

If exotic species are taking over from the natives, how are our native mosquitoes faring?

Well there is at least one native species that may actually be threatened. Maorigoeldia argyropus is a very large (and rather beautiful mosquito) that is particularly interesting because it seems to have lost its ability to feed on blood. There are no records of this species doing so in the wild, and all laboratory attempts to induce feeding on blood failed. This is one native mosquito that is well adapted to a forest environment, and there is some evidence that the species appears to be restricted to relatively large and mostly pristine areas of native forest. It seems that due to its strong association with such environments, Maorigoeldia argyropus has been disappearing from many areas throughout the country as the original native forest has been progressively removed.

Feature image source: Wikimedia Commons.

To learn more about how climate change may affect our health , visit Royal Society Te Apārangi’s Climate Change and Health

These interviews are supported by Royal Society Te Apārangi, which supports New Zealanders to explore, discover and share knowledge.




18 Responses to “Mosquito-borne diseases more likely to reach New Zealand”

  • First, according to NIWA New Zealand has not warmed for the last 19 years and we now know that, at the very least, the IPCC climate models overestimate global warming by a factor of two. This means that the models are virtually worthless so we can conclude that nobody knows what future temperatures will be. There is a strong possibility that the world will soon start on a cooling cycle.

    Secondly, any mosquito problem can be solved easily and safely by using DDT. According to the World Health Organisation it is still the safest and most effective way of combating mosquito borne diseases. Yet it did not get even a mention. Why?

    I’m surprised that it got past review.

  • Bryan –

    You wrote,

    “I’m surprised that it got past review.”

    There is no review of that nature at Sciblogs, the content is the writer’s.

    any mosquito problem can be solved easily and safely by using DDT

    DDT is banned in many countries as part of an international action, and my understanding is that only a few countries regularly use it. In the case of NZ, “The use of DDT in New Zealand was banned in 1989 due to negative environmental impacts” (Source: Wikipedia: ) It might be effective at killing mosquitos, but it’s use is a balancing act against environmental and human health issues. This seems at odds with your claim re WHO, are you sure you have read correctly?

    according to NIWA New Zealand has not warmed for the last 19 years

    Climate change isn’t my patch but I see that the NIWA 7 series anomaly graphs overall look (strongly) positive for the past 20 years; this doesn’t seem consistent with your statement re NIWA. Is your statement from other’s re-analysis of NIWA rather than their own work?

    There are examples of insect shifts due to climate change, and from that change in distribution of insect-borne disease. My “favourite” is the rise of tick encephalitis in northern Europe, a story I’ve considered telling on Sciblogs.

  • Dear Grant,
    “WHO gives indoor use of DDT a clean bill of health for controlling malaria”

    Sets out the WHO policy for using DDT.

    You may not know that WHO scientific staff lobbied strongly against the Rachel Carson inspired total ban on DDT. But the politicians won and, as a result it has been estimated that 20 million people or more died unnecessarily. Most of them children in developing countries. You could call it mass murder.

    As I spend quite a lot of time working in Africa and other developing countries, (and, so far, I have avoided malaria) I feel quite strongly about this. They are real people and we should not deprive them of the best available remedies for political reasons.

    “When South Africa stopped using the pesticide in 1996, malaria deaths increased by one thousand percent (South Africa has since resumed DDT sprayings). Latin America saw an increase of 1.8 million malaria deaths in the 1980s and 1990s after dropping DDT.”

    As you can see, relying on Wikipedia is not a good idea.

    Here are the NZ temperatures from NIWA from 1997 to 2016. 2017 will be cooler. I can’t show a plot but the trendline is slightly downwards. 2017 and 2018 are likely to be cooler because a La Nina is predicted. It always causes cooling.

    As my father used to say “Believe nothing of what you hear and half of what you see”. It is always a good starting point.

    If you used your influence to lobby for a return to using DDT in New Zealand and the Pacific, it would do a lot to safely get rid of dengue and other mosquito borne diseases.

    PS Rachel Carson claimed that DDT was causing raptors to have weak eggshells. Yet, Over the same period, raptor populations were increasing. There is a strong possibility that her research was shonky.

  • @Bryan Ah, the legacy of Silent Spring. Spread enough uncertainty and doubt and the damage can be irreversible. There’s no chance DDT will be introduced back into NZ. The EU is even on the verge of banning use of glyphosate.

  • Hi Brian,

    Thanks. I don’t mind corrects about science, but object to characterisations about me – sorry.

    I’d didn’t “rely on Wikipedia” as you make out. You seem to be reading a (quite!) different meaning into my words, and are making assumptions.*

    If you want to write things like “As my father used to say” around, you’ll know that old saw about assumptions, right?

    Also: I also have spent quite a bit of time in developing nations and so far have avoided malaria, etc. I’m hardly overlooking that they’re people, etc., and any implication that I don’t care about or consider others is very offensive. (FWIW I’m currently in the Lao PDR.)

    *The reference to Wikipedia only applies to what I quoted and nothing else I wrote. Saying I “relied” on that statement misreads me, and you’ve made out I wrote all I did from Wikipedia which is incorrect. I quoted the full paragraph (it’s only one short sentence after all) as not to quote mine a selected phrase; in any event the quote is giving the reasoning given for the action (at the time), not anything about me! As for the rest, I quickly looked up a small number of papers in the research literature, as I do. Too few! – I’m short on time. One weakness of reading a small selection of papers is that each individual paper might be weak, or not aligned with the wider picture; another problem is that you sometimes have to dig very deep to sort out some statements properly – both part of the reason I put it to you as a question. If the wider/deeper picture is different, thanks, but be careful not to “frame” how others do things, or imply they’re thoughtless of others, etc.

  • @Peter,

    Yeah, I’d forgotten about the Silent Spring angle when I wrote!

    I agree that reinstating DDT use in NZ would be a tough act.

    The glyphosate nonsense is really unfortunate, a real case of blowing away something using wayward reasoning.

  • Grant
    I don’t think the issues that are now coming to light out of the glyphosate reclassification are something as innocuous as “wayward reasoning”. The multiple changes made to the final draft of the text ( were deliberate and the person who made them has gone to ground, indicating that they have something to hide. The fact that the man in charge of the IARC committee made money advising lawyers who had brought cases against Monsanto indicates that the could be corruption involved. At the very least, there is serious conflict of interest.

    It is things like this, and the story behind DDT, that do a lot of damage to science, making it easier for the anti-vaxxers or the like to justify their cause.

  • Peter, if you think that the EU is justified in banning glyphosate because it is (as is apparently stated in the paper) as cancer-causing as coffee, I suggest you change your job. If it is banned, more risky and less effective chemicals will have to be used in its place. It is always wise to look at the big picture.

    I noticed that no one has challenged the NIWA data that I posted.

    Jacob, be careful in Laos. I presume you have heard all about the bombies. Rather more dangerous than malaria I suspect.

    • Bryan- the NIWA data posted shows deviations (=anomalies) from the NZ average temperature since 1909. If the temperature was unchanging, there would be as many negative as there are positive anomalies. If it was cooling we would see more negative than positive anomalies. Your posted data from NIWA rather shows, that *most* of the anomalies in this period are positive. That’s what warming looks like. That distribution of the data alone shows that NZ temperatures are warmer in the last two decades, than in any previous two.

      The trend-line since 1909 is unequivocally positive. There is nothing of merit to an argument that removes *most* of the data (1909-1996) to identify a trend. This is especially the case for climate where over short time periods, temperatures can be volatile. I suspect that even extending the data back to 1991 would show that the trend for temperatures is upward, given the clustering of ‘cool’ anomalies in the early 1990s.

      • It looks like both Brendan and Bryan are right because you are talking about different things.
        The relevant point is whether the 20 year trend has any significance. The IPCC show the trend extrapolated to 2100 as exponential. That would mean a linear trend is not the appropriate statistical analysis tool. If evaluated as a quadratic, the trend line would be an inverted parabola, so temperatures would be expected to drop. Time will tell.

        • No, we’re not talking about different things. I’m criticising Bryan’s claim of a downward trend in temperatures being observable. My first point, in more detail, was that the inter-year variation in temperatures is far greater than any measurable trend in temperatures (over such a short time period/small number of observations). You’re not going to pick up any trend over that time period with this much volatility.

          My second criticism is that in order to manufacture this trend, most of the NIWA climate data has to be thrown away. This is indefensible. The only way to pick up a trend of small incremental change in temperature is to have a large data set. You don’t throw away data. At best it is naive. At worst it is cherry-picking.

          As much as I’d like to see evidence of global temperatures leveling off and even falling, the data provided by NIWA does not support this. It’s entirely depending on a tiny number of observations at the end of the series, all within scope of year-to-year variations. That has no statistical power.

      • There is no doubt that world temperatures have increased in the last hundred years or more. The early 1900s were usually cold and much of the warming took place from the 1900s to the 1940s, then there was a decrease in temperatures until 1975 followed by an increase from 1975 to about 2000. Since then temperatures have been steady. 15 years ago David Wratt told me that we would have to wait at least 10 years before we decided that the failure of the climate models to predict actual temperatures indicated she was problems with them. It is now 20 years of effectively no warming.

        The possibility that the climate changes naturally and the model predictions are worthless cannot be avoided.

        If you do have convincing evidence that man-made greenhouse gases cause dangerous global warming, there is a $6000 prize waiting for you at the website of the New Zealand climate science coalition. Go for it!

        • I’m not following you down this rabbit hole Bryan. The issue was the NIWA data and your assertion that 20 years sufficed to detect a trend. You have had the opportunity to defend that, and you can’t. That’s because your claim deviates wildly from sound statistical analysis. Likewise throwing away data (why get rid of the early 90’s observations for instance?) appears suspicious. So we’re done. You’ve had your chance.

  • Bryan,

    Peter, if you think that the EU is justified in banning glyphosate because it is (as is apparently stated in the paper) as cancer-causing as coffee, I suggest you change your job. If it is banned, more risky and less effective chemicals will have to be used in its place. It is always wise to look at the big picture.

    Peter wasn’t suggested it ought to be banned, he was implying it’s a shame that it would be.

    I noticed that no one has challenged the NIWA data that I posted.

    Doesn’t mean anything. People might just not feel like bothering. (You might want to consider that people are tired of your stuff on climate change.) I believe others have already addressed you on that elsewhere.

    Jacob, be careful in Laos. I presume you have heard all about the bombies. Rather more dangerous than malaria I suspect.

    My name is Grant, and my surname is Jacobs with an ‘s’. Should I call you Leylan? 😉

    Personally if I were you, I’d have taken the opportunity to apologise or clarify re your first response to me.

    re UXOs (incl bombies), while dramatic to think about, and traumatic for those affected, it shouldn’t be a difficult problem for the vast majority of visitors. Just stick to well-used paths and roads, don’t randomly wander off into fields, forest, etc. Locals are much less able to avoid the issue 🙁


    • “My name is Grant, and my surname is Jacobs with an ‘s’. Should I call you Leylan? ”

      You have done so already. My name is Bryan, not Brian. But it worries me not at all.

      Poor people in developing countries suffering from malaria because of the actions of rich environmentalists who have ignored the evidence and those in Laos still at risk from bombies from an undeclared war does worry me.

      • Byran,

        You have done so already.

        OK, so I made a mistake earlier, but one that is very obviously an innocent mistake, and you write a deliberate troll/stunt in reply??? You could have just politely pointed it out if it bothered you so much.

        My name is Bryan, not Brian. But it worries me not at all.

        Personally, I’d guess it does bother you or you wouldn’t have written your silly stunt. My apologies for the error, but I don’t think it deserves the way you’ve treated me here (I’m including the other things you’ve written).

        Aside from that you’re playing this truly silly pissing competition where you keep trying put yourself on a pedestal. (I can’t help noting you’ve shifted your goalposts a little to try keep standing on your pedestal, too.)


  • Re NIWA & the coming summer – they have a ‘climate outlook’ online. This currently predicts a weak & short-lived La Nina (

    It also includes the following statement: November 2017 – January 2018 temperatures are forecast to be above average for all regions of New Zealand (60% to 70% chance for above average temperatures). Coastal water temperatures around New Zealand are forecast to remain above average over the next three-month period, especially along the east coast of the South Island.