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mangrove challenge

Surviving spraying

Photo of a mosquito
A female mosquito biting a toe.
Photo: Jeff Wright, QM

Photo of mosquito wrigglers
Wrigglers breathe at the surface of still water, and need little food. Their development can be stopped by larvicides.
Photo: QIMR

People who live near mangroves may have a mosquito problem caused by Aedes (Ochlerotatus) vigilax, the Saltmarsh Mosquito. It is the main pest mosquito in coastal areas of Queensland. Mosquitoes rarely breed in mangroves. Instead, they lay their eggs on the surface of brackish pools in marshy areas near mangroves where their larvae, or wrigglers, can develop. Adults often shelter by day in mangroves, where they feed on sap and nectar from mangrove trees. Before they can form eggs, female mosquitoes need a protein-rich blood meal, so they bite people and other animals. When they do this they can also transmit blood-borne diseases such as Ross River virus, so mosquito control can be needed for public health reasons.

Local councils in Queensland spray for mosquitoes from September to March, because heavy rains and extra high tides make any dormant eggs hatch. They often use methoprene, a larvicide, because it targets mosquitoes. It mimics the effect of juvenile hormones, and stops pupae developing into adults. Research into the effects of methoprene on animals has mainly been done in the laboratory, but field tests undertaken by a University of Sydney scientist showed that methoprene applied at low concentrations delayed development in tadpoles of Green Tree Frogs.

Housing and canal development, the draining of wetlands and the spread of weeds all increase the area of stagnant water and make conditions favourable for mosquito breeding. Management methods including runnelling - opening gutters to allow water to flow through saltmarsh areas - reduce the mosquito problem. Control measures such as spraying chemicals in these sensitive areas should always be a last resort.

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