Natural way to get rid of mozzies

Zoo's project uses bednets and insect-eating creatures to reduce mosquito population
Leow Si Wan, Straits Times 12 Dec 09;

Kevin Lee (left) and Troy Tan were among four Hwa Chong Institution students roped in by pest-control company Origin Exterminators to help in the zoo project. They sometimes offered themselves as human bait to lure and kill mosquitoes to count how many there were. -- ST PHOTO: DESMOND FOO

THE Singapore Zoo has enlisted some environmentally friendly allies in its battle to reduce the number of mosquitoes on site.

Instead of traditional pest-control methods such as fogging and misting, the new troops are insectivores - such as frogs, spiders and fish - which eat the larvae and adult mosquitoes.

This, said assistant director of zoology Biswajit Guha, allows the zoo to manage the mosquito population while maintaining an ecological balance.

Starting in March and working with pest-control company Origin Exterminators - which was one of the sponsors - and four Hwa Chong Institution (HCI) students, the zoo began a pilot project using a combination of insectivores and bednets to reduce its mozzie count.

Bednets are sewn from pieces of mosquito net embedded with a non-soluble and non-volatile insecticide.

The results: An average 60 per cent drop in the number of mosquitoes across the five test sites from the time the insectivores and bednets were first used to last month, when the project wrapped up.

Said Mr Carl Baptista, head of research and development at Origin: 'When the zoo first approached me with the idea of using its natural environment to deal with mosquitoes, I was very sceptical about the effectiveness of insectivores.

'I roped in the Hwa Chong students to help execute the project and we couldn't even find research papers on this subject.'

The zoo, he added, switched to Bti misting - a way of killing mosquitoes using bacteria, which does not affect the environment - from fogging about eight years ago as conventional insecticides are harmful to flora and fauna.

The National Environment Agency also does not encourage the use of fogging as a primary means of controlling the mosquito population.

For the project, the native insectivores, which also included dragonfly nymphs, were released at sites within the zoo and the Night Safari. Ponds were also constructed so these insectivores could be sustained in a suitable habitat that is also favourable to mosquitoes.

These bug-loving creatures are 'a natural control agent for mosquito populations', said Mr Guha.

To monitor the number of mosquitoes on a weekly basis, the HCI students used ovitraps - contraptions that trap mosquito larvae - and 'human baiting'.

Said 16-year-old HCI student Troy Tan: 'We stood there and let the mosquitoes land on us before smacking them with our hands so that we could count the number.

'The highest record was about 40 mosquitoes in half an hour.'

Their itch-inducing sacrifice and weekly visits to the zoo were not without reward: The team of Secondary 4 students - Troy, Kevin Lee, Darren Choo and Tan Wei Xiang - will represent Singapore in a community problem-solving competition to be held in the United States next June.

Meanwhile, the zoo will look into enhancing the aquatic ecosystem of existing ponds and moats, and creating new ones to encourage more native insectivores to come on board.

Said Mr Guha: 'While it must be complemented with environmentally sustainable conventional mosquito management techniques, it should improve what we have been doing, and in a way which encourages biodiversity.'