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$700,000 study on bug situation

PUB, NEA and NUS join forces to control midge problem. -TNP
Teh Jen Lee

Wed, May 16, 2012
The New Paper

The authorities apply non-chemical larvicide BTI twice a day at Pandan Resevoir when there is a spike in midge larval counts.

SINGAPORE - They may be small, but the task to keep their numbers in check is a big one.

Chironomids are a type of midge or fly that does not bite, and they do not transmit diseases. But when they swarm, they are a nuisance to residents near Pandan Reservoir in West Coast.

The national water agency, PUB, and the National Environment Agency (NEA), have spared no effort in controlling the midges there. They are doing the same at Bedok Reservoir, which has also seen midge outbreaks in the past.

Last Tuesday, PUB, NEA and scientists from the National University of Singapore (NUS) met more than 20 members of the West Coast Garden Neighbourhood Committee to update them on the midge situation. PUB and NEA have partnered NUS in a $700,000 study that began in January and will go on for three years.

The vice-chairman of the neighbourhood committee, Ms Olivia Khong, said the meeting was a "fantastic effort".

"It was like a one-hour science lesson, but no boring stats. The relevant people were there, including a professor and deputy director from PUB, to answer our questions," she said.

There will be a similar meeting on May 21 with Ayer Rajah grassroots leaders.

The peak period for swarming at Pandan appears to be during June to July, so efforts are being stepped up now.

A booklet in four languages has been produced to educate residents about midges and inform them on what is being done to prevent swarming.

Jointly produced by PUB and NEA, it will be distributed this week at more than 60 blocks near the reservoir. The booklets, which has details on monitoring and measures taken to suppress midge numbers, will also be given to residents in the Bedok Reservoir area.

The monitoring efforts involve twice weekly larval counts, nightly drives along the reservoir dike to look for swarms using headlamps and daily inspections of housing blocks facing the reservoir for adult midges.

These measures are carried out by the 13 PUB staff and two contract workers at Pandan, as part of their reservoir management duties.

The larval count is energy-intensive. It takes a whole day to take sediment samples from 11 points in the reservoir, wash out the larvae, and manually count them using a plastic dropper.

This reporter tried doing that and found it was not easy to pick up even three larvae as they kept wriggling away.

Some of the larvae are so small that a microscope has to be used to verify that they are indeed midge larvae.

Imagine how much work it took when the larval count registered more than 2,000 during a sharp peak earlier this year.

Technical officer Norhisam Mohd Bolhim, 42, said: "(My) Eyes get very tired - put (eyedrops) also no use."

He was one of the 45 participants from PUB, NEA and NUS who were trained by Professor Peter Cranston, a well-known midge expert from the US, in a nine-day workshop that was part of the NUS study.

Larval count monitoring is crucial because it acts as an early warning system. Mitigation measures are stepped up when four out of the 11 sample points exceed 100 larvae, or the total for all the points exceeds 1,000.

Already there is daily removal of the eggs from the underside of the jetty or other floating structures by two contract workers using scrub brushes.

It takes about a week to cover the reservoir, which, at 176ha (about 200 soccer fields), is one of the largest reservoirs in Singapore.

There is also fogging once a week and application of the non-chemical larvicide Bacillus thuringiensis israelensis (BTI) once every two weeks during "peace time" as PUB executive engineer Roderick Ho puts it.

But when larval counts go up, then fogging and BTI application are both done twice a day.

"We don't take any chances," said Mr Ho.

Preventive measures

Other measures include:

  • installing netting along the water edge
  • turning on strong white light at the reservoir pumping station at night to attract midges away from residential areas
  • introducing wetland vegetation to help promote habitat creation for midge predators such as dragonflies

So far, the efforts have paid off - there was no major swarming event at Pandan Reservoir last year. Besides the work of the authorities, the booklet lists measures that residents themselves can take to reduce the problem of midge swarms, such as installing insect screens and using yellow lights instead of white lights.

Mr Raymond Khoo, 26, a research student who has lived in a block facing the Pandan Reservoir, has noticed a vast improvement in midge numbers.

He remembers seeing lots of midges when he was growing up, with the worst outbreak happening in 2010.

"It got so bad that the floor would covered with dead midges in the morning. It was hard to clean," he said.

"Now, the problem is minimal. There are even fewer midges than 10 years ago. I think what they are doing is sufficient."

This article was first published in The New Paper.

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