A quest to find the world’s only hot pool mosquito

A quest to find the world’s only hot pool mosquito

Did you know there’s an endemic species of mosquito that exclusively occurs in New Zealand’s thermal pools? We don’t know much about this species, so in October and March, bug expert Julia Kasper made it her mission to find it – a mission that included a harness and a gas monitor, ʻin case of toxic gas eruptions’.

Julia by a hot pool wearing a harness and holding a bowl on a long stick
Julia sampling, wearing a harness, 2020. Photo by and courtesy of Stephen Dogget

The history of Culex rotoruae – the Rotorua mosquito

Culex rotoruae is thought to be exclusively found in the Taupō volcanic zone, Rotorua, and also at Ngawha Springs in Kaikohe.

Map showing the locations of the Taupō volcanic zone, Rotorua, and also at Ngawha Springs in Kaikohe
Map showing the locations of the Taupō volcanic zone, Rotorua, and also at Ngawha Springs in Kaikohe

The hot pool-loving mosquito was first collected and described in 1962.

Since then, there has only been a few records or findings. We have barely any adult mosquitoes of this species in the Te Papa collection, and no larvae.

To make matters more complicated, the records of the pool locations, including their temperature, are very vague.

The records told me that the larvae are only found in the mineralised water of thermal springs, and have been found in clear and turbid waters, with widely varying mineral levels, and a pH level anything between pH8.5 and pH5.6.

Temperature records range from around 27 °C but there is also a record from 1944 of larvae found behind the old baths in Rotorua with a temperature of 37 °C!

Finding the Rotorua mosquito

So off I went on a quest to find the only hot pool mozzie in the world (that we know of).

During my fieldtrips I checked out sites in Rotorua and Taupō.

In Rotorua I sampled from the hot pools in the Kuirau Park with its more than 100 little pools and springs, Sulphur point, Wai-O-Tapu, Kerosene Creek, and Tikitere.

And in Taupō, the Tokaanu Thermal Pools.

The most successful sites in terms of numbers was Kuirau Park.

Steaming hot pool. It's an orange colour and there are dead trees around the outside.
Kuirau Park, 2020. Photo by and courtesy of Stephen Dogget

I also found larvae in an overflow puddle from a pipe for Tokaanu’s baths in Taupō where they use the thermal water for their pools.

Pipe partly out of the ground with a puddle around it
Pipe at Tokaanu’s baths, 2019 Photo by and courtesy of Hannes Kasper

Not all the sites I visited were positive, but I did find larvae in different types of water – the most common type being milky green coloured water with a low pH.

Julia sat on a board walk leaning over a turquoise colour hot pool
Julia sampling at Wai-O-Tapu, which had the hottest positive sample site, 2020. Photo by and courtesy of Stephen Dogget

Even gas bubbles, making the water appear as if it’s boiling, obviously cannot stop the larvae.

Looking inside a white bowl, with lots of mosquito larvae in it
Culex rotoruae larvae, 2020. Photo by and courtesy of Stephen Dogget

What temperature were they living in?

The temperature varied a lot. Clearer water was often cooler at around 25 °C, whereas the milky water could have high temperatures.

The temperature can change a lot within a pool over time and will have hotter patches. For example, a pool at the Kuirau lake was 60 °C in the middle but I found mosquitoes at the rim where it was ‘only’ 30 °C –  this is quite high for an insect to survive.

The highest temperature we could measure for the larvae was at Wai-O-Tapu with 34.4 °C.

Steaming hot pool, it's a dark turquoise in the middle and bright orange around the outside
Wai-O-Tapu’s champagne pool, 2020. Photo by and courtesy of Stephen Dogget

Because of the unstable ground, and the dangerously high temperatures the mud and the water could reach, I needed to wear a harness as well as a gas monitor in case of toxic gas eruptions.

There are still so many sites I would have loved to have sampled from, many almost inaccessible (despite my harness) – for instance, this lake near the Kerosene creek that looked very promising:

A green-coloured steaming lake surrounded by forest
Lake near Kerosene Creek, 2019. Photo by Julia Kasper. Te Papa

Are the Taupō and Rotorua mosquitoes genetically different?

There’s a good chance that the mosquito populations from the Rotorua and Taupō locations could have been isolated for a long time. So I’m really interested to find out whether the specimens collected are genetically different.

Why do they live in warm water?

We don’t know much about these mosquitoes at all. We’d like to know more about why they choose to live in these warm waters – benefits for thermal pool insects could be the lack of predators, and the ability to breed all year round.

Why is it important to know more about them?

The interesting bit for us could be analysis of their heat shock proteins (HSP). HSPs are produced by cells in response to stressful conditions, such as heat, but as well as to cold or UV light. They are important to stabilise or repair damaged protein due to the stress exposure.

This sort of research can be helpful in increasing the effectiveness of cancer vaccines, understanding autoimmune reactions, or stress tolerance to hybridized plants.

Its place in the World’s Weirdest Mosquitoes book

My quest was really well timed because I received a request by my Australian colleague Stephen Dogget to include this little New Zealand fella in his new book, World’s Weirdest Mosquitoes.

So we raised the larvae and pupae we found to adulthood, and Stephen took the most beautiful images.

Culex rotoruae can now claim its rightful place as one of the world’s weirdest mosquitoes.

Close-up photo of a mosquito perched on a human's hand
Female Culex rotoruae, 2020. Photo by and courtesy of Stephen Dogget
A close-up of a mosquito perched on a human's skin
Male Culex rotoruae, 2020. Photo by and courtesy of Stephen Dogget
A larvae with hairs on it at the water's surface
Culex rotoruae larvae, 2020. Photo by and courtesy of Stephen Dogget
Pupa curled up and floating at the top of the water
Culex rotoruae pupa, 2020. Photo by and courtesy of Stephen Dogget

2 Comments

  1. Avatar

    Fascinating! The photos are really good – so much detail.

  2. Avatar

    Amazing, never thought about such a thing existing since those hot springs always seem so scary and inhospitable! Loved how the difficult missions to the hot pools wound up producing such fantastic pictures too.

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