Urban sprawl, climate change help nasty mozzies

Urban sprawl and development combined with climate change see New Zealand troubled by more foreign, disease-carrying mozzies, scientists say. Photo / Angus McIntosh, University of Canterbury

Urban sprawl and development combined with climate change mean New Zealand is troubled by more foreign, disease-carrying mozzies, scientists say.

A University of Canterbury study looked at how mosquito numbers and species might change as the planet warmed - and how shifts in land use could affect the picture.

It came as biosecurity officials recently found exotic culex mosquitoes - known the carry the feared Ross River virus - in the Kaipara Harbour this month.

The researchers specifically investigated how mosquitoes were affected by differences in land cover and climate.

"We looked at two species that are commonly found here in New Zealand and which people are probably familiar with as they are trying to get to sleep: Culex pervigilans, which is a native mosquito, and Aedes notoscriptus, a stripy-legged Australian invader," study author Sophia Hunt said.

Mosquitoes spent the early stages of their life cycle in standing water habitats, such as ponds, puddles and water containers.

The researchers found that climate and land use affected both how suitable their habitats were, and how many of them there were in place.

Warmer habitats made mosquitoes and the other insects living in the water eat more, faster, and go through their life cycles faster.

"At the same time, warmer water means the predators also eat more, faster," said Hunt, who collaborated on the study with Canterbury colleagues Dr Mark Galatowitsch and Professor Angus McIntosh.

"We found that different mosquito species react slightly differently to the change in temperature, and to predation."

The effects were more pronounced when land use was taken into account.

"There are more, smaller, warmer habitats available in human-modified environments, and these are also less likely to contain other insects that might be predators of mosquitoes."

As we changed the land and our climate, many foreign species were on the rise and many native ones were declining.

The University of Canterbury's Sophie Hunt has been studying what helps mosquitoes to spread. Photo / Angus McIntosh/University of Canterbury

"This has flow-on effects for humans, because some of these new species, such as mosquitoes, can bring disease," Hunt said.

"The way that species interact with each other is important, because some species can help to control numbers of unwanted species like mosquitoes."

But it wasn't all doom and gloom, Hunt said.

"It's important to remember that we have an element of control over the situation – we can create habitats that support predatory insects that act as natural biocontrols against mosquitoes.

"And not all mosquitoes are bad – most of the New Zealand native ones don't even bite humans, and they can act as pollinators."

New Zealand is home to 15 mosquito species, 12 of which aren't found anywhere else in the world.

Some of the mosquito habitats analysed in the study. Photo / Angus McIntosh/University of Canterbury

Since our arrival, several new species have become permanently established here and we've stopped dozens more at our ports, and eradicated one.

Among the least-wanted were species such as Aedes albopictus - the Asian tiger mosquito - and Aedes aegypti - known as the yellow fever mosquito.

These were 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, University of Auckland senior research fellow Jose Derraik said last year.

However, due to temperature limitations it would probably be restricted to the northern tip of New Zealand.

But Aedes albopictus was one of the world's worst invasive species, and it could establish under our temperate climate.

Importantly, it was an efficient vector of a number of important human pathogens, such as dengue fever viruses or Zika virus, and could breed in a wide range of microhabitats in close association with humans.

This is a species that would be of major concern, because it would greatly magnify the likelihood of an outbreak occurring in our country.

People could help fight the likelihood of foreign ones invading by emptying out potential water habitats like tyres and containers, and by creating permanent ones - such as ponds - that encouraged insects like dragonflies, beetles and bugs to eat their lavae.