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Sherry Lee

Global warming blamed for proliferation of insects

Climate change isn't only making  Hongkongers sweat.  It's also making them itch.

Along with  sweltering temperatures have come hordes of biting midges and blackflies  that have swarmed  over the New Territories and some  urban areas, infuriating residents and damaging  businesses.

Experts say the tiny insects favour hot and wet weather, and their proliferation is a result of global warming.

The Food and Environmental  Hygiene Department  refuses to  admit that the biting pests - recognised as a serious nuisance to humans and other mammals in many countries - are a severe problem.

But the number of complaints it receives  has grown  from 15 in 2004 to 151 last year. From January to July  there were 206 complaints, most from Sai Kung.

Yuen Long district councillor Chow Wing-kan  said the insects had become a  nuisance and urged the government to  act.

At least two families of biting insects are known to be causing the nuisance. The department,  which hired a Beijing expert to study the problem in 2004, identified 20 species belonging to the family of midges known as Ceratopogonidae,  which generally breed under wet soil.

And Kadoorie Farm entomologist Roger Kendrick  said he had witnessed an increasing number of biting blackflies,  all belonging to the family Simuliidae,  which cause an itchy swelling lasting three to five days.   The senior conservation officer of the fauna conservation department at Kadoorie Farm said the  blackflies' arrival showed that 'nature is taking revenge on human beings' for  environmental damage.

The FEHD  noticed that the problem began in the northern districts and border villages in the early 1990s, when massive felling of trees  on the mainland brought flocks of birds.  The insects' eggs were spread in their droppings.

But  Dr Kendrick said that the boom  had more to do with global warming, which brought heat and heavy rain. 'Heavy rains speed up water flow in streams and rivers and increase oxygen in water,'  where blackflies can thrive.

Another entomologist, Clive Lau Siu-ki,   of the Agriculture, Fisheries and Conservation Department,  said hot weather can also  help  biting midges breed much more quickly.

Cheung Ka-yun,  head of the FEHD's contract management and insect control unit, said the department used the same control methods as for mosquitoes: cutting grass, clearing rubbish and spraying river channels and drains.

But both entomologists said the department was on the wrong track.

Mr Lau said  biting midges lived in the soil so just cutting the grass was no use. He suggested spraying pesticides on the soil.

Dr Kendrick said blackflies did not breed abundantly in polluted water channels and it is no use spraying there. He suggested  breeding natural predators such as dragonflies and damselflies  and releasing the larvae in streams, marshlands, container yards and construction sites.

Mr Cheung rejected this,  saying that dragonfly larvae did not breed in polluted water channels. But Mr  Kendrick said that the department should simply put the larvae in  clean streams.

Friends of the Earth said the FEHD shouldn't reject the  advice without  trying it.

The green group's director, Edwin Lau Che-feng,  said that the department could start a pilot scheme to test the proposal.

Biting back

Facts about biting midges (Ceratopogonidae)

They mainly bite  at dawn and dusk  on still, cloudy days.  Itching often starts  hours later.

Residents seem to  develop bite immunity.

Salt marshes  and highly organic wet soil are  breeding grounds.

Control methods include draining and   luring  them with carbon dioxide to an insecticide-treated target.

Facts about blackflies  (Simuliidae)

Blackflies can  be so persistent  that outdoor activity  without  protection becomes almost impossible.

They are attracted to mammals by  exhaled carbon dioxide and moisture,  and dark colours.

They transmit  filarial worms  which can cause blindness.

Removal of vegetation  in streams will  reduce the number of larvae. Temporary damming of water can reduce populations.



Rising temperatures are bringing hordes of pests