The New Zealand landscape, particularly the lowland areas, has been converted, in the very short time span of about 200 years, from forest and swamp to open farmland and towns, with small remnant patches of native environment.

While this may underpin the national economy, Dr Mary McIntyre and her colleagues at the Ecology and Health Laboratory, University of Otago, Wellington, also see a downside.

"We're trying to understand the relationship between ecological change and risks to human health, in particular the establishment of disease organisms and the ways people might come in contact with them," she says. "Put simply, we have made things a whole lot better for many of those creatures which cause us problems!"

This includes mosquitoes, which are a considerable nuisance and cause of allergy in some areas, but do not yet carry human diseases in New Zealand.

McIntyre and her team have been piecing together a picture of influences on mosquito activity around semi-rural Waikanae, north of Wellington, and rural Manawatu, where they are a considerable nuisance in some years. It seems that new dynamics are developing with these tiny opportunist insects.

"Some mosquitoes are doing well on land that has converted to dairying, where irrigation plus excess nitrate in groundwater and cattle troughs are ideal. At the same time, other native species are in decline with the loss of native forest environments, and two of these are possibly endangered."

This research is looking at how aspects of recent change - in particular, some effects of rural subdivision, continuing reduction in and degradation of remaining native areas, and the expansion of dairy farming and irrigation - are creating favourable conditions for mosquito populations.

"The first essential for this work is a pair of gumboots. The next is the goodwill of landowners and district councils allowing us access to trap adult mosquitoes and to check out likely breeding sites. Both have been very supportive and, of course, most have their favourite 'mozzie' stories! The great part is that we get to work outdoors, especially in the summer which is when mosquito numbers build up."

There are 12 identified native New Zealand mosquitoes and four established exotics, at present. The researchers have found a build-up of two exotic species north of Wellington that seems to be quite recent. Both carry human viruses in other parts of the world. The Ecology and Health Laboratory now has data from several projects on mosquito populations as a basis to test new hypotheses about mosquito occurrence and human exposures in these areas.

"Put simply, we have made things a whole lot better for many of those creatures which cause us problems!"

"Mosquitoes are extremely sensitive to micro-climates and, if you change the land cover and the standing water available, then you change the mosquitoes, perhaps allowing new ones to move in. People and farm animals are new hosts that were not previously available."

And, while mosquito bites are an irritation, there is a more serious concern. There are increasing numbers of visitors and returning New Zealanders who are infected by mosquito bites overseas and then bring infections into this country. There is now the risk that they may be bitten again by local mosquitoes, which then transmit the virus to another mammal or human.

"If this happens often enough you get a build-up of viruses in a host population. This may result in the development of a critical mass of infected animals or people in a particular area which can lead to an outbreak of illness such as Ross River virus and dengue fever," she says.

"This, plus the effects of environmental change and the warmer and wetter climates predicted for the future, make the establishment of mosquito-borne illness here only a matter of time."

There is yet another side to mosquito research - the beauty of the insect itself when seen through a microscope. McIntyre says many are stunning, with beautiful silver scales and ornate antennae (males), adding an aesthetic dimension to her original research.