Why some mosquitoes are helpful in controlling disease

Mosquitoes may well be the most famous bloodsuckers around.

Small, sneaky and leaving an itchy bite, the buzzing blighters are more than just annoying, they can also be dangerous, spreading a range of diseases that can make you extremely sick.

However, not all mosquitoes should be seen as “the bad guys.”

MOSQUITOES OF AUSTRALIA
Entomologist* and author of Eyes on Flies, Dr Bry the Fly Guy, has done a lot of research on mosquitoes, which are a type of fly. He said there are 230 known species of mosquitoes that live in Australia and more than 200 of these are considered native.

“They’re the ones we know of,” he said. “We actually know there’s 170 extra unnamed mosquito species.”

A few years ago, Dr Bry picked up the unfinished work of the late Australian mosquito expert Dr Elizabeth Marks*, who discovered these unnamed mozzie species.

Now Dr Bry has begun identifying and naming some of these extra species.

“Not all of them are bad,” he said. “There are many that don’t have a role in spreading diseases.”

BENEFICIAL MOZZIES
Dr Bry said many native mosquitoes played a positive role in the ecosystem*.

“There’s a type called the elephant mosquito,” he said. “They’re called elephant mosquitoes because the larvae* are so big, like elephants. They live in tree hollows when they fill up with water and they’ll actually eat other mosquito species’ larvae – so they’re getting rid of the bad guys for us.”

VEGETARIAN MOSQUITOES
The elephant mosquito is one of many varieties of mosquito that don’t drink blood. In fact, generally speaking, male mosquitoes are vegetarians.

“It’s only the female mosquito that bites, because she needs the protein* in our blood to ripen her eggs,” he said. “Male mosquitoes and some species are completely vegetarian – they just drink nectar and eat pollen from flowers all day long.”

DANGEROUS BITING MOZZIES
There are also quite a few biting mosquitoes that play a role in spreading dangerous viruses among humans. The common banded mosquito, culex annulirostris, a native mosquito that is widespread in Australia, may have been responsible for spreading a recent outbreak of Japanese encephalitis*, Dr Bry said.

“There’s a handful of other species that can transfer viruses like Murray Valley encephalitis*, Ross River virus* – the common banded mosquito transfers those viruses as well,” he said.

HOW MOSQUITOES SPREAD DISEASE
Diseases are spread when an infected person is bitten by a mosquito. The germs from the infected person are transferred into the mozzie’s salivary glands*, and when that same mosquito bites another person, the germs are injected into the new person’s bloodstream because of the “backwash” that occurs from the mosquito’s mouth.

“It’s not the mosquito’s fault,” he said. “It’s the viruses and bacteria that have hijacked the biology* of the mosquito.”

KEEPING DANGEROUS MOZZIES OUT
While mosquitoes in Australia can carry dangerous viruses like Japanese encephalitis, Ross River fever, Barmah Forest virus*, Kunjin virus*, and Murray Valley encephalitis, there are mozzies in other parts of the world known to transmit other serious diseases like dengue fever*, malaria*, zika* and yellow fever*.

People travelling to countries where these mosquitoes pose a risk should get vaccinated against these diseases wherever vaccines are available and take measures to protect themselves from being bitten by mosquitoes.

There are mosquitoes in South-East Asia like the Asian tiger mosquito, which could move further south into the Torres Strait towards Australia as climate change warms the planet.

“We definitely want to stop it there from coming further into Australia,” Dr Bry said. “It can transmit diseases like dengue and zika virus.”

LIFE CYCLE OF A MOSQUITO
Most mozzies don’t live very long. While it takes up to a few weeks for an egg to develop into an adult mosquito, the actual mozzie usually only lives for a couple of days or weeks depending on the species.

Life starts as an egg laid in a raft* on water. The egg hatches into larvae, which then usually go through a few stages of development before turning into pupae*, which look like little balls in the water. There they rest for a couple of days before emerging as an adult mosquito.

“There are some species that kind of go into hibernation, like a bear,” Dr Bry said. “They might hunker down in an enclosed dwelling or a cave and they can survive for a long period of time. They sleep it off and wake up and lay more eggs.”

WHERE THEY LIVE
Mozzies can be found all over Australia and in most parts of the world.

“This is why mosquitoes are so successful,” Dr Bry said. “They can live in any area of Australia. There’s a species called culex sitiens that lives in rockpools by the beach, its larvae live in salty water. There’s mosquitoes that live in arid areas of Australia and there’s mosquitoes that can live in freezing environments in Tassie too.”

HOW TO PROTECT YOURSELF
Even though not all mozzies bite, it’s best to avoid them because of the health risks they pose, said Dr Bry.

You also can’t tell the difference between species or males and females unless they are under the microscope.

“Most mosquitoes come out at dusk and dawn so it’s best to avoid going outdoors then,” he said. “But if you do have to go outside, wear long sleeves and long pants. And one of the best ways is wearing a topical insect repellent so you smell nasty to a mosquito.”

He said using a fan on your porch can help keep mozzies at bay.

“If there’s a lot of wind blowing, the mosquitoes can’t fly into that,” he said.

Having flyscreens on your windows will stop them coming inside your house while getting rid of any pools of water in your garden will reduce the number of places they can lay eggs.

POLL

GLOSSARY

• entomologist: a scientist who studies insects
• Dr Elizabeth Marks: (28 April 1918 – 25 October 2002) an Australian entomologist who was instrumental in the discovery and naming of new species of mosquitoes as well as the eradication of Aedes aegypti, which spread Dengue fever, in the Brisbane area during the mid 1950s
• ecosystem: the way plants and animals in an environment interact
• larvae: the active immature form of an insect
• protein: complex molecules that are essential for much of the body’s processes and structures
• Japanese encephalitis: a virus spread by mosquitoes that mostly causes mild fever and headache or no symptoms but can sometimes lead to severe illness, permanent disability and even death
• Murray Valley encephalitis: a rare but potentially serious infection of the brain caused by the Murray Valley encephalitis virus that is spread by mosquito bites
• Ross River virus: the most common mosquito born infection in Australia, causing joint pain, fever and a rash
• salivary glands: glands in the mouth that produce saliva
• biology: body parts
• Barmah Forest virus: a mosquito born virus that causes fever, chills, headache, joint swelling, stiffness in the mornings, a rash and fatigue
• Kunjin virus: a mosquito born virus causing fever, enlarged lymph nodes, rash, swollen joints and fatigue
• Dengue fever: a virus that is spread by mosquitoes that causes fever, severe tummy pain, swollen glands and a faint red rash. People can become very sick from Dengue fever and sometimes even die from it. Most parts of Australia don’t have Dengue fever however there are still outbreaks each year in northern Queensland after people catch it overseas and then get bitten by a mosquito once they return to Australia
• Malaria: a life-threatening disease spread by some types of mosquitoes that is caused by five different parasites. Malaria is both preventable and curable
• Zika: a mosquito born virus that can cause problems for the unborn babies of pregnant women who become infected
• Yellow Fever: a virus spread by mosquito bites that can make you so unwell your skin turns yellow
• raft: a cluster of eggs that floats on the water
• pupae: the stage in-between larvae and adult, where the insect is in a state of rest and transformation

EXTRA READING
Aussie bloodsucker series: leeches
Aussie bloodsucker series: lice
Aussie bloodsucker series: fleas

QUICK QUIZ
1. How many known species of mosquito are there in Australia?
2. Why is it that only females drink blood?
3. What do so-called vegetarian species of mosquitoes feed on?
4. What diseases does the Asian Tiger mosquito spread?
5. Why is the Elephant mosquito useful to have in the garden?

LISTEN TO THIS STORY

CLASSROOM ACTIVITIES
1. Life cycle of a mozzie
Show the life cycle of a mosquito by creating a diagram. Each stage should have a picture, a label and a brief description.

Time: allow 20 minutes to complete this activity
Curriculum Links: English; Science

2. Extension
In this news story we are told that not all mosquitoes should be seen as “the bad guys.”

Let’s imagine that you are Marco the Mozzie and you’ve been magically transformed into a human-sized talking mosquito, tasked with convincing humans that you (and your mozzie mates) are not bad guys. Write a speech with some facts and some humour that might persuade humans to stop swatting you.

Time: allow 30 minutes to complete this activity
Curriculum Links: English; Science; Drama

VCOP ACTIVITY
Let’s practise taking notes
When note-taking, we want to be able to extract the key pieces of information from the text or presentation. You start with determining the main idea: if you had to explain to someone in a sentence what the article is about, what would you say?

Then back up the main idea with two to four key points to support what you first stated.

What would you put as the main idea and supporting points to back up this article?

Once you have had a go at note-taking.

Share your results with a peer to see if you identified the same information or different.

Discuss the finding if you came up with different information.