Māori used crushed leaves of the ngaio tree (Myoporum laetum) to deter mosquitoes and sandflies. They also doused their bodies with oil, and with kōkōwai (red ochre) when working naked in the fields. To soothe itchy bites, they applied a juice made from crushed ngaio leaves or from fronds of rarauhe or bracken fern (Pteridium esculentum).
The simplest way to avoid bites is to cover up, especially when sitting or standing still – sandflies tend not to bite moving targets. They rarely bite indoors or after dark, and are not found above the bushline.
One of the best ways to reduce mosquito numbers around the house is to remove all standing water from clogged drains and elsewhere, as this is where they breed. When camping, cover up well, and avoid swampy areas. In mosquito-prone places, a fully enclosed tent with mesh screens is essential. Repellents should also be used.
West Coast gold miners rubbed rancid bacon on their skin in the 1860s. When the minister for public works, Richard Seddon, rode the track from Paringa to Haast in 1892 he coated himself with camphorated lard, which he deemed a success. Also effective are home-made concoctions of olive oil mixed with disinfectants such as Jeyes Fluid or Dettol. Citronella oil, used in sprays and candles, or in skin lotions, can help keep insects at bay.
Insect repellents for the skin are effective against sandflies and mosquitoes. The active ingredients in many repellents are known by the abbreviations DEET (diethyl toluamide) and DIMP (dimethyl phthalate). DEET is the most effective repellent. It has been used by millions of people worldwide since 1957, and has a very good safety record. It is recommended that repellents used on children contain less than 10% DEET.
Eat it to beat it?
Many people believe you can repel sandflies or mosquitoes by swallowing garlic or vitamin B (for instance in the sandwich spread Vegemite), or drinking beer from a flagon to which a capful of kerosene has been added. But there is no evidence that anything taken orally works against these insects.
All repellents need to be regularly reapplied. DEET-based products are typically effective for one to six hours.
Relief from bites
Sandfly and mosquito saliva contains anticoagulants (to keep blood flowing) and agglutinins (to prepare blood for digestion). These cause allergic reactions such as itching, redness and swelling. Reactions vary, and compared to newcomers, local people seem to be less bothered by sandfly bites. As they have been bitten before, their bodies may not react as strongly to the proteins in sandfly saliva.
Sandfly and mosquito bites should not be rubbed or scratched, as this can inflame the bite and break the skin. Itching and swelling can be soothed by antihistamine cream or calamine lotion.
Although overseas species of blackfly can carry and transfer diseases, there are no records of New Zealand’s biting sandflies doing so. Nor have any mosquito-borne human diseases from a local source been recorded. Mosquitoes do transfer the Whataroa virus among birds on the West Coast, but this does not appear to kill or make birds ill.
Three introduced mosquitoes – the brown house mosquito, the saltwater mosquito and the striped mosquito – are able to transmit human and animal pathogens or parasites overseas. Four endemic species – Culex pervigilans, Opifex fuscus, Culiseta tonnoiri, Aedes antipodeus – may also carry and transmit diseases, but this is untested. Since the 1930s at least 30 species of exotic mosquito have been intercepted at New Zealand ports. Most of these can carry and transmit diseases.
Global warming will produce warmer temperatures throughout the country, and wetter conditions in its western regions. As temperatures increase, some mosquito species are likely to spread southwards, and there will be greater potential for exotic species to breed.
Acknowledgements to Paul Leisnham and José Derraik.