Dengue, Zika and Wolbachia

Townsville has been trialling an innovative way of eliminating Dengue, one of the nastier tropical diseases, for the past eighteen months. Its basis is infecting the Aedes aegypti mosquitoes (photo – wikipedia), which carry the virus, with Wolbachia bacteria which prevent the virus developing.

The April 2016 Field Trial Update (pdf no longer available) is full of good news:

A year and a half after releasing the first mosquito with Wolbachia in Townsville, we are excited to announce that almost all Aedes aegypti mosquitoes are now carrying Wolbachia across the Stage 1 area.

Wolbachia levels in Townsville City, South Townsville, North Ward, Belgian Gardens, Castle Hill, West End, Garbutt, Gulliver, Currajong, Vincent, Aitkenvale, Mundingburra, Hyde Park, Pimlico, Mysterton, Hermit Park and Railway Estate are all between 80% and 100% and we hope to see this trend continue long-term. … We are making strong progress towards our goal of establishing Wolbachia in Townsville’s mosquito population, and reducing the risk of dengue transmission in our city.

… We are grateful to the more than 6700 locals who have joined our team. Townsville is setting an example for what communities can achieve when locals lend a helping hand.

… Meanwhile, communities in Cranbrook, Heatley, Kirwan, Thuringowa Central and Mount Louisa have been the first to grow and release their own Wolbachia mosquitoes using DIY Mozzie Boxes. Wolbachia levels in these suburbs are increasing and we will continue to monitor the population as the release phase in these areas comes to an end.

When we signed up for the trial we (and most of the rest of the world) hadn’t even heard of Zika virus, but Zika is the reason those Mozzie Boxes have been in the international news recently:

For the past several years, researchers in Australia have been at work trying to develop a way to put a stop to dengue, a virus that — like Zika — is spread by way of a certain breed of mosquitoes.

The result is what’s called a Mozzie Box, and Susan Desmond-Hellmann, CEO of the Bill and Melinda Gates Foundation, recently demonstrated how it works.

The Mozzie Box works by intentionally breeding disease carrying mosquitos, with a twist.

In the Mozzie Box, Aedes mosquitoes — the same kind that transmit diseases like Zika, dengue, yellow fever, chikungunya, and more — are bred.

And how exactly is breeding more mosquitoes the solution to a mosquito-borne illness?

The Mozzie Box mosquito eggs contain a bacteria called Wolbachia, which renders the grown mosquitoes essentially harmless (minus a few itchy bites here and there).

The whole story of Dengue (which we’ve had in Townsville forever), Zika (which we’ve never had) and the mosquitoes is too long and complicated to tell here but this Wikipedia page covers the science well enough to ground further reading on the World Mosquito Program site and elsewhere.

Butterflies and other insects on the Town Common

Here are some of the insects I saw on the Town Common yesterday – far more numerous than the birds I talked about in my previous post, although I have to say that wasn’t entirely a Good Thing (more on that later).

Butterflies

  • Marsh Tiger, Danaus affinis
  • Lesser Wanderer aka Plain Tiger, Danaus chrysippus
  • Common Crow, Euploea core
  • Blue Tiger, Tirumala hamata
  • Common Eggfly, Hypolimnas bolina
  • Blue Argus, Junonia orithya
  • Bush Brown, Mycalesis sp.
  • Grass Yellow, Eurema sp.
  • Clearwing Swallowtail, Cressida cressida
  • Black-spotted Flash, Hypolycaena phorbas

Of these, the first two are always abundant on the Common and the next three are nearly as common. All five are about the same size. The next three are all smaller. They are also common but are trickier to identify because close relations in each genus look so much alike (which is why I have just said “Eurema sp. [species]” and so on). The last one is the odd one out, belonging to a different family (Lycaenidae) and being much rarer.

Marsh Tiger butterfly
Marsh Tiger
Plain Tiger butterfly
Lesser Wanderer or Plain Tiger
Common Crow
Common Crow

One of my reasons for posting these three photos as a set is that they happen to show all three species feeding on the same kind of flower, the Tridax Daisy.

Black-spotted Flash
Black-spotted Flash, female

Lycaenidae (Blues) are usually quite small but this one is bigger than most, about the same size as the Grass Yellow.

I did also see many other small butterflies and moths but they were impossible to keep track of.

Dragonflies

Golden dragonfly
Golden dragonfly, unidentified
Red dragonfly
Common Glider, Tramea loewii

Standing water always means dragonflies and they were as numerous as the butterflies. Once again, I couldn’t begin to identify all of them and I’m just posting a couple who posed nicely for me.

And the rest

Add together the numbers of butterflies and dragonflies and you might be close to the total number of grasshoppers; add together the grasshoppers, butterflies and dragonflies and you might be close to the total number of mosquitoes – or that’s what it felt like! The Common is not a place to visit without repellent in the Wet season.

Most of the mozzies were the little standard-model grey-black types but one, seen below attempting to drill through my pants leg, was special enough for a photo.

Brown mosquito
Brown mosquito

She (males don’t suck blood) was about twice the average size – perhaps not as big as the magnificent Metallic Mosquito, but close.

My oddest discovery of the trip was this:

Pandanus leaf
Pandanus leaf

Pandanus leaves are spiked along the edges but this one – and others on the same plant – seemed to have pairs of supernumerary spines coming from the lower face of the leaf. A closer look revealed that each pair of ‘spines’ was a pair of wings attached to plant hoppers (Derbidae, Hemiptera), each of which was attached to the leaf via its proboscis (properly called a ‘stylet‘) and earnestly sucking sap from a vein.

sap-suckers on leaf
Derbid plant-hoppers feeding on pandanus

After the rain

pink and white bottlebrush flowers on tree
Bottlebrush flowers on the tree after the rain

We had our first cyclone of the season last week but it was only a little one (Dylan, category 2 at its biggest) and Townsville  was on the northern edge of its path so its main effect on us in Mundingburra was about 60mm of very welcome rain over two days. (Some suburbs did suffer more, I know, particularly from the storm surge on the Thursday morning. I don’t mean to be dismissive of their losses but I’m writing about my own little part of the city.)

The plants responded enthusiastically to the rain, none more so than the pink and white bottlebrush (Callistemon; I think it’s  a hybrid cultivar) in front of the house.  The insects, in turn, responded enthusiastically to the flowering plants and I have had fun seeing just how many different kinds I could spot on this one tree:

brown and white beetle on flower
Brown Flower Beetle, Glycyphana stolata, a scarab
black and yellow wasp on flower
A flower wasp, Campsomeris radula
Large mosquito on bottlebrush foliage
Metallic Mosquito, Toxorhynchites speciosus

The Metallic Mosquito is a very large species but does not, thankfully, attack humans. In fact it makes itself useful to us by preying on other mosquitoes. (One expert in Thailand counted some 420 species of mosquito of which a mere couple of dozen ever fed on people. Mosquitoes are victims of their bad press just as much as spiders are.)

Green bee amongst the stamens
A small native bee, Colletidae family

There were perhaps a dozen of these bees around the tree at any one time, making them the most numerous of the insects enjoying the flowers (which included, incidentally, some tiny black beetles which were too small and dull to photograph successfully).

Taking advantage of all of them, or trying to, were some predatory spiders – Lynxes – lying in wait amongst the flowers. I saw two different species. Both these spiders are very small, about the size of a house fly.

orange-brown spider on leaf
Lynx spider (Oxyopes genus) on bottlebrush leaf. It has a grey abdomen
brown spider with spiky legs
Lynx amongst the stamens