SINGAPORE: The current dominant midge species that has recently emerged at Pandan Reservoir is a rare one that has not been studied in great detail, said Minister for Environment and Water Resources Masagos Zulkifli in Parliament on Monday (Sep 2).
“The species exhibits different behaviours from other species. For example, they hide in drains and culverts in the day and swarm above the drains in the evening,” he added.
The minister was replying to parliamentary questions from MPs about the rise in the midge population at Pandan Reservoir and the measures being taken to address it.
Providing details, he said PUB has greased drain walls to trap midges when they land to rest, and have targeted these areas for fogging.
PUB has also explored the use of free-moving oily paper within drains to increase the capture rates of adult midges, he added.
The netting on the reservoir dyke has also been extended by 1km, said Mr Masagos, acting as a barrier to trap adult midges and reduces the number of adult midges that would otherwise be blown to residential estates.
“Midges cannot be eradicated as they are part of the natural aquatic ecosystem, and will emerge to breed, especially when aided by favourable environmental conditions. Climate change will further complicate our efforts,” he added.
PUB said in a Facebook post on Aug 1 that it has stepped up measures to control the rising midge population around Pandan Reservoir.
These include increasing the frequency and dosage of biological liquid larvicide within the reservoir, increasing the frequency of fogging and misting around the reservoir dyke and surrounding vegetation, as well as the installation of bright spotlights at the Pandan Reservoir pumping station to attract adult midges when they emerge at night, said Mr Masagos.
According to PUB, the bright lights deter them from flying into residential estates. Midge egg masses attached to floating structures and rocks along the edges of the reservoir have also been removed.
Speaking in Parliament, MP for West Coast GRC Foo Mee Har said residents who live near Pandan Reservoir have “suffered greatly” from the mass emergence of midges since July this year.
“Their homes have been invaded by the midges. Corridors, lifts and bus stops have been swarmed. And the midges stick to your clothes, your hair, fly around your eyes, get into your nose, get into your food, and they’re everywhere.
“This year’s outbreak is the most severe we have witnessed yet and also persisted for the longest time, impacting the daily lives of our residents. Some have likened it to being in a horror movie. If you visited it's really scary.”
Ms Foo raised concerns about the health risks of exposure to chemicals from sustained fogging, and whether residents could be supported with insect screens for their homes as such installations can be costly.
Mr Masagos said the pesticide used by PUB has been certified safe and suitable for use by the World Health Organization, and is also diluted before use.
As for the installation of insect screens, Mr Masagos noted that the residents can also protect themselves and their property.
“This situation doesn’t come all the time, not every year. And to put in something that will become a permanent feature, this may also affect the image of the reservoir or the places around the reservoir,” he added.
Mr Masagos also explained that the larvicide used in the reservoirs is a safe, biological larvicide.
“It is actually a naturally occurring soil bacteria, which produces spores that are toxic specifically to the digestive system of midge larvae.”
Underscoring the importance of maintaining water quality, he added: “There is a trade off between killing enough midges, or killing so much or everything that we kill ourselves. We can’t do that either. There is a limit to which these measures can mitigate the issues that residents are facing.
“This problem is really man versus nature, the kind of war man has never been known to win. We can only suppress it and do our best but we have to live with nature. In fact, we are the ones who are intruding into their living spaces.
"Our reservoirs supply drinking water to the population and we have to be careful to ensure that PUB’s mitigation measures, both short- and long-term, do not end up compromising water quality."