The London (down) underground mosquito

 August 5, 2013

Our latest publication in the Australian Journal of Entomology marks the end of a three year research project investigating the biology of a unique introduced mosquito species, Culex molestus, in Australia.

We generally think of nuisance-biting mosquito problems being confined to tropical regions, or at least warm summer conditions. Well, imagine you’re in London in late September 1940. You’re taking shelter in the underground during The Blitz. It is crowded and cold. You’re bitten by mosquitoes too. You’re being bitten by Culex molestus. It is often commonly referred to as the London Underground mosquito and has already been the subject of some fascinating research that has shown how the mosquito has adapted to life within the London underground.

Culex molestus was first described from Egypt in 1775. The mosquito is unique in that it is closely associated with subterranean habitats across the temperate regions of the world, from underground train networks to flooded basements to septic tanks. The species has adapted to these habitats by gaining the ability to mate without the need to swarm (a phenomenon known as stenogamy) and by dropping the requirement of a blood meal to develop the first batch of eggs (a phenomenon known as autogeny). You can read about our previously published work on this here.

Londoners take refuge in the Underground during the Blitz. Taken from “The Tube 150 Anniversary: London Underground, Its Life In Pictures ” Huffington Post UK

The Culex pipiens subgroup of mosquitoes includes a number of globally important vectors of disease-causing pathogens but there are distinct genetic and biological differences between these species that influence their role in transmission cycles. There are four member of the Cx. pipiens subgroup in Australia, Culex australicus, Culex globocoxitus, Culex quinquefasciatus and Culex molestus.

The last of these species, Cx. molestus, had not been the focus of substantial research for over 50 years until a research project by the Department of Medical Entomology and University of Sydney commenced in 2010. The project was designed to address the gaps in our knowledge of these species with a view to assisting in the assessment and management of disease risk associated with this species.

This work was primarily undertaken by Nur Faeza Abu Kassim as part of her PhD candidature with generous support from Ministry of Higher Education Malaysia andUniversiti Sains Malaysia.

How did the mosquito get to Australia?

The most cited theory to explain the introduction of Cx. molestus into Australia is that it was through military movements into Melbourne during World War II. This was based on an absence of this species in Victoria during the pre-WWII period. Our research supported this theory.

There were no reports of this species in Australia prior to the 1940s. A review of distribution records for this species confirmed the presence of the species at over 230 locations confirmed that the mosquito has spread throughout the southern parts of Australia and in coastal regions as far north as Tweed Heads (NSW) and Geraldton (WA). No specimens have been reported from Queensland or Northern Territory.

Molecular analysis of specimens collected from throughout Australia, with reference to specimens from Asia, North America and Europe, indicated that Australian Cx. molestusshared the strongest genetic similarity with specimens from Asia. Perhaps the mosquito hitched a ride from Japan into the Pacific and then, with US military, in Australia?

An example of subterranean habitats closely associated with the presence of Culex molestus

Buzzing (and biting) about all year long?

One of the interesting findings of our research was that the mosquito was active throughout the winter months around Sydney. Analysis of weekly trapping over a 13 month period indicated that the species does not display diapause. As well as generally being a cool-temperate climate mosquito species, perhaps the subterranean habitats provided a little “insulation” from the cold, keeping water temperatures just a little warmer than above ground pools and ponds?

Most of the other nuisance-biting pests disappear during the cooler months. There will occasionally be a few about, particularly during warmer winter days. However, for most local pest mosquitoes, it seems to be the minimum daily temperatures that drive mosquito activity more than maximum daily temperatures. In the case of Cx. molestus, they soldier on regardless.

What about the public health risks?

One of the last unanswered questions regarding the potential public health impacts of Cx. molestus is in relation to the ability of this mosquito to spread local and/or exotic viruses. While local viruses (e.g. Ross River virus) have been isolated from field collected specimens, there is yet to be a thorough investigation of the ability of this species to transmit endemic pathogens such as Murray Valley encephalitis virus or Kunjin virus.

I was involved in a research project assessing the risks posed in eastern Australia due to potential introduction of West Nile virus. Laboratory investigations and field collectionsprovided some valuable information but, due to prevailing environmental conditions at the time, there were very few Cx. molestus collected during the study. We need to complete some of this work to gain a better understanding on how important a role Cx. molestusmay play in local disease risk.

One of the key implications of our research is that it highlights the need for urban planners and engineers to consider the risks posed by above and below ground water storage for creating mosquito habitats. While much of my work previously has concentrated on the creation of wetlands and rehabilitation of other habitats in association with urban development, rainwater and storm water storage structures should be adequately designed to reduce mosquito risk.

The full reference for our most recent paper is below:

Kassim NFA, Webb CE and Russell RC (2013) Australian distribution, genetic status and seasonal abundance of the exotic mosquito Culex molestus Forskal (Diptera: Culicidae).Australian Journal of Entomology 52: 185-198 [online]

ABSTRACT. Culex molestus was probably introduced into Australia in the 1940s and represents a potentially important nuisance-biting pest and vector of disease-causing pathogens in urban areas. The aims of this study were to review the literature to determine the current and historical distribution of Cx. molestus in Australia, analyse the genetic similarity of specimens collected from various locations in Australia with reference to specimens from North America, Asia and Europe, and document the seasonal abundance of this mosquito in the Sydney region. Results showed that Cx. molestus is common in southern Australia, but there was no evidence that this mosquito is found north of latitude 28.17°S. Molecular analysis indicated that specimens from various locations throughout Australia shared strong genetic similarity and that it was most likely introduced from Asia, possibly through multiple introductions over the past 70 years. Analysis of the seasonal abundance of Cx. molestus indicated that the species does not display diapause during the cooler months. Consideration should be given to the unique biology and ecology of this species when assessing the public health risk and the surveillance methods required in the management of Cx. molestus within urban areas of Australia.

You can read a media release from the University of Sydney here. Our research was picked up by the local and international media in the past week or so too. You can read about our work in the Daily Telegraph, Newcastle Herald and Sydney Morning Herald.

New Mosquito Repellent Made, "Better Than Anything Else"

Formula uses human compounds to block mosquitoes' sense of smell.

Mosquitoes avoid a hand treated with DEET (right).

Photograph by Greg Allen, USDA-ARS

Christine Dell'Amore

for National Geographic

Published September 17, 2013

Mosquitoes bugging you? There may be a new repellent on the horizon—and it's "so much better than anything else we've ever seen," its inventor says.

A few years ago, Ulrich Bernier was busy blending various chemicals together in the lab, hoping to figure out why the blood-sucking insects bite some people more than others. Mosquitoes home in on their targets by sniffing out various chemicals and bacteria on human skin.

When he created one blend with a group of chemicals that are very similar to ones found in low concentrations in our bodies, Bernier noticed that the bugs seemed to ignore it. (Read what happens inside you when a mosquito bites.)

These chemicals—which include the tongue twisters homopiperazine and 1-methylhomopiperazine, among others—seemed to have an incredibly robust ability to mask our scent from mosquitoes, said Bernier, a research chemist at the United States Department of Agriculture's Agricultural Research Service.

Next, Bernier and colleagues set up an experiment where people put their arms or hands inside a cage full of mosquitoes. The insects avoided the skin of the subjects when the chemical cocktail was released from a container inside the cage.

Bernier and colleagues created a formula of several chemicals for a repellent, which was approved by the U.S. Patent and Trademark Office in 2012.

"It's a pretty neat discovery because I don't think anyone else has shown chemicals this capable of blocking skin odors that are normally attractive to mosquitoes," said Bernier, who presented the research at the American Chemical Society meeting in Indianapolis last week.

Why do we need a new repellent?

Insect-borne diseases are prevalent and potentially dangerous. According to the U.S. Centers for Disease Control and Prevention, there are about 30,000 annual reported cases of Lyme disease, which is transmitted by ticks, and at least a thousand annual cases of mosquito-caused encephalitis—which includes West Nile virus—in the country. Bernier and colleagues' new repellent is also effective against other blood-sucking insects.

The most common insect repellent now in use is DEET, which is designed to be sprayed on the skin. However, there has been some concern about DEET and potential toxicity, and there's high demand for equally effective alternatives. (See"Mutant Mosquitoes Not Repelled by DEET.")

How does it work?

Bug repellents like DEET work by deterring mosquitoes that find the smell unappealing; the new formula actually makes you invisible to the insect.

Here's an analogy to explain the two: If you walk into a room and smell something bad and leave, that's how DEET works. But with the new repellent, it's as if you walk into a room and don't smell anything, Bernier said.

Bernier said it's unknown why insects can't smell the compounds.

How is the repellent applied?

Commercial availability is still far down the road—there needs to be more toxicology tests on the formula, as well as field tests, Bernier cautioned.

But he said that it could be used indoors or outdoors and would probably work best released into the air rather than applied to the skin. For example, the repellent could be emitted from a sealed canister that releases a vapor slowly into the air, creating a sort of protective bubble around your environment.

For instance, if you're sitting outside on a patio, you could install several canisters around the patio, he suggested.

Nanoparticles stop mosquitoes breeding

23 September 2013William Bergius

Most mosquitoes lay their eggs in stagnant water and this is where the eggs develop into larvae © Shutterstock

A simple synthesis for environmentally benigncarbon nanoparticles that could be used to control mosquito populations has been demonstrated by scientists in India.

Mosquitoes are found across the globe, with the exception of Antarctica and Iceland. A holiday nuisance, they are also a well-known vector for many diseases, including malaria, dengue fever, yellow fever and viral encephalitis. The transmission of diseases by mosquitoes is estimated to be responsible for 2 million deaths every year.

Control or eradication of the mosquito population could significantly restrict the spread of disease. Screens and nets can be used to exclude the pests, while traps or insecticides can be used to eliminate them. More permanent solutions include draining pools of stagnant water where mosquitoes like to breed, or the introduction of natural mosquito predators such as dragonflies.

Sabyasachi Sarkar and his team of inorganic chemists at the Bengal Engineering and Science University have now come across a new answer to the mosquito problem. When trying to take pictures of zebrafish, that had been fed on mosquitos treated with water-soluble carbon nanoparticles (wsCNPs) to help with the imaging, they noticed that the presence of the wsCNPs appeared to be retarding the development of the mosquito larvae.

After further investigation, Sarkar and his team were able to show that a concentration of these wsCNPs as low as 3mg/l prevents the larvae from ever reaching maturity, resulting in their death. At this concentration, the wsCNPs are otherwise harmless to the surrounding environment and can persist in stagnant pools of water for periods of several months.

The nanoparticles are made by burning wood wool in a reduced oxygen environment, washing them and then treating them with nitric acid. ‘It is an easily scalable process,’ says Sarkar, ‘the mosquito eradication programs run by different government agencies across the globe should try this method, particularly in cities with poor drainage.’

‘It's very positive that the wsCNPs exhibit a high persistence in water and the local environment, as opposed to other synthetic insecticides that can quickly degrade,’ says Pilar Mateo, a leading specialist in the control of endemic disease transmitting vectors and President of Inesfly Corporation. However, she warns that further research is needed into potential long term ecological effects, before this material can be implemented as an effective method of vector control.

Sarkar’s team will now focus on gaining a better understanding of the mechanism that prevents larvae maturation. Suppression of the hormone, ecdysone, is suspected to be a factor and this could have vast implications for further research on mosquito control.

REFERENCES

M Saxena, S K Sonkar and S Sarkar, RSC Adv., 2013, DOI: 10.1039/c3ra44100h

New insect repellent can make humans invisible to mosquitoes

Posted Fri 11 Oct 2013, 11:23am AEDT

PHOTO: Scientists say they have invented a repellent that makes humans virtually invisible to mosquitoes.(AAP: University of Queensland, file photo)

MAP: Perth 6000

Scientists say they have invented a repellent that makes humans virtually invisible to mosquitoes.

US-based scientist Ulrich Bernier studied chemical compounds in the skin of people who are usually left alone by the blood-sucking insects.

He concocted a new formula that masks the chemical that attracts mosquitoes to some people.

University of Sydney Medical Entomologist, Dr Cameron Webb, said the science could be incredibly useful in mosquito-prone areas of outback Western Australia.

"It's about having a delivery method which is better," he said.

"So if we can stop having to put on lotion, and maybe just flip a switch on a device or spray something around the room it's going to be much easier and much more effective in providing protection against biting mosquitoes."

Dr Webb said it could eliminate the need for spray-on lotion or smoking coils.

"We'd love something like a smokeless mosquito coil that we could just set in motion in the room and that would protect us from mosquito bites."

"Identifying some of those chemicals in a study like this provides an opportunity to highlight some potential chemicals that we can investigate into the future."