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Tangle of Life: The buzz on repelling mosquitoes

In Byron Shire, the most commonly found species is thought to be Aedes notoscriptus. Photo contributed

Mary Gardner

Emergency resilience. My phrase for our knowledge and practices from year to year in response to great ecological cycles. One of these is water, turning from scarcity to deluge and back. The other is vegetation, from growth to fire and back. The past year finishing with Cyclone Debbie tested many of us across large areas of Australia and New Zealand. What we are ready to do is the strength or weakness of our community’s emergency resilience.

One part of emergency resilience concerns mosquitoes. After the flood, we’re hearing some calls for aerial spraying to kill them. The reasons why this would be ineffective is revealed in the 2012 Byron Shire Council report. In 2011, mosquito traps caught 31 diverse species: 14 Aedes, 9 Culex, 3 Coquillettidia, 2 Verellina and one each of Culiseta, Masonia and Uranotenia. These distinctions are of practical importance.

At the crux are the individual life-cycles and the habitat that each species prefer. The general life-cycle is basic. After mating, the female needs a blood meal to ripen the eggs. This protein can come from biting birds, frogs, reptiles, mammals and of course, people. She lays eggs in water, where the larvae hatch, feed and grow before emerging as a flying adult insect. This cycle can occur from as little as five days to as long as several months including hibernation during a cold season. The 400 species globally each have their own special take on this cycle.

Aerial sprays would only kill some species and individuals of only a certain age. Sprays would require many repeats. Meanwhile the poisons badly affect aquatic species and other beneficial insects.

Far better government spending would be to help people with knowledge and gear to help themselves. How about an emergency programme offering information sheets about species in the area? Present instructions about draining buckets and other water pockets around yards and buildings. Offer free screening materials, so people could set up barriers across open tanks and troughs. This would prevent access by certain mosquitoes.

See, in Byron Shire, the most commonly found species is thought to be Aedes notoscriptus. Its life-cycle takes advantage of human habitation. Larvae grow up in less than a week, making do in small pockets of water in the yard and gutters. Adults do not travel far from where they emerge and tend to lay eggs nearby. They are short-lived but tend to carry the virus for Ross River and Barmah Forest diseases. Emptying standing water and putting up barriers disrupts this life-cycle.

A wise emergency response, given the recent rise in cases of Ross River virus, would be to protect people in flood affected areas with free supplies of personal repellents.

Other Aedes species lay eggs in soil at edges of water bodies whose levels rise with rains or tides. They quickly hatch and emerge as clouds of adults, quickly repeating the cycle while the water is around. As the water levels fall, the cycle pauses and the eggs wait for a change in the weather or tide. The Coquillettidia also carry the same viruses but these hatch in freshwater wetlands. The adults don’t travel far from where they emerge, so people are more likely to encounter them when they go into these areas especially at dawn and dusk.

A wise emergency response, given the recent rise in cases of Ross River virus, would be to protect people in flood affected areas with free supplies of personal repellents. The chemical DEET insecticide mixtures are effective. The National Geographic kits out its explorers with effective botanical mixtures, which are at least 15 per cent essential oils. Creams with less than that don’t work well. Mosquitoes favour the scents of people with Type O blood and beer drinkers in a sweat.

The Culex have a similar life-cycle but their preferred habitats are drains, pits and septic tanks rich with organic pollutants. Sometimes ponds, clear or with vegetation, are also habitats for these and other species. Here, an emergency response would be to offer free ‘mozzie dunks’: small doughnuts made of a crystal protein from Bacillus thuringiensis israelensis (Bti). This only kills the larvae of mosquitoes. The dunks slowly dissolve and continue to kill only the target animals, without building immunity.

Finally, Byron Shire Council’s mosquito management plan is five years old and due for review. The action plan called for continued mosquito trapping but this was suspended in 2013.

The plan also called for amending the DCP. New housing should be set, as Ballina does, at over 100 m away from wetlands and waterways. Tweed is even more site specific: from 50 m to 1 km away. These water bodies should be rehabilitated, re-introducing native fish that eat mosquito larvae: Pacific Blue eye Pseudomugil signifer Empire Gudgeon Hypseleotris compressa, Firetail Gudgeon Hypseleotris galii or a range of Rainbowfish (Melanotaenia species.)

So, are both council and community up for this?


One response to “Tangle of Life: The buzz on repelling mosquitoes”

  1. m gardner says:

    FYI Mozzies buzz because they have parts at the base of their wings that rub together as they fly. Each spcies has their own sound and as a male and female get together they adjust their buzz until they match each other and then they mate. The researchers at Stanford have used this bit of biology to come up with a simple way for communities to monitor mozzies. Residents can catch mozzies in jars and use their cell phones to record the buzzing. The species making these recordings can be identified. http://abuzz.stanford.edu/

    Here is a review of some of the various monitoring projects in the EU http://www.mosquitoalert.com/en/a-new-paper-collects-citizen-science-initiatives-for-mosquito-surveillance-in-europe/

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