The 200 million yuan ($32 million) Guangzhou spent last year on mosquito control to prevent dengue fever went to more than just buying pesticides, officials said in response to public questions.

The money was also used to cover other costs, including purchasing and repairing equipment for mosquito control in drainages and paying temporary workers' salaries, said Xu Lifan, a health official of Guangdong province, Shanghai-based news portal thepaper.cn reported on Sunday.

The Guangzhou government invested nearly 200 million yuan last year to eliminate mosquitoes - which spread dengue - in response to the most serious surge of the fever that the city had seen in recent years, the Guangzhou Urban Management Commission said on Friday.

The commission had not previously given details on the spending, which spurred public questions on why so much money was used for killing mosquitoes.

Xu said a large portion of the money went to improving mosquito control infrastructure, which was lacking or failed to work properly because of poor maintenance and management.

"So 200 million yuan is not a big sum considering it helped improve the infrastructure that had been neglected in the past years because of lack of investment," he said.

Guangzhou mobilized 24 mosquito control campaigns since June to gain control of the dengue outbreak, during which a total area of 3,291 square kilometers was sprayed with pesticides, according to the Guangzhou Urban Management Commission.

The city had more than 35,000 dengue cases last year, and five deaths were reported, the commission said.

Guangzhou has made preparations for earlier mosquito control this year, the commission said.

Besides using pesticides to kill mosquitoes, authorities have also taken other measures, such as stocking waterways with the larvae of mosquito fish (Gambusia affinis), which eat mosquitoes.

Excessive reliance on pesticides to kill mosquitoes has been criticized.

"Mosquitoes are extremely reproductive, and it is impossible to totally eliminate them," said Wu Mingliang, chief engineer of Guangzhou Huicheng Pest Control Co.

In addition, he said, mosquitoes can gradually become resistant to pesticides, leading to the use of more and stronger pesticides, which can seriously harm the environment.

"The consensus among pest control experts has been that long-term and excessive use of pesticides can make pests stronger," he said.

And pesticides also kill natural enemies of mosquitoes such as spiders and frogs, and this damages a city's biodiversity, he said.

"Authorities should abandon their reliance on chemicals to control pests and employ more advanced pest control methods that can protect the environment," he said.

Xu Ruiheng, a researcher at the Guangdong Provincial Center for Disease Control and Prevention, said many factors can lead to the spread of the dengue fever, such as the public health system being undermined by density of population, favorable environment for the reproduction of mosquitoes and climate change.

Although vector control through chemical or biological targeting of mosquitoes and removal of their breeding sites is at the core of dengue prevention, this approach has failed to stop disease transmission in almost all countries where dengue is endemic, he said.

Improvement of the environment and living conditions is the key to preventing infectious diseases, he said.

wangxiaodong@chinadaily.com.cn