Releasing mosquitoes to fight dengue: How Singapore took Project Wolbachia from lab to heartlands

Singapore is releasing mosquitoes to fight dengue, an idea that initially sounded counterintuitive but has moved from laboratory research into housing estates across the island.

Project Wolbachia began in 2016 after years of research and risk assessments. The effort gained momentum following one of Singapore’s worst dengue outbreaks in 2013, when more than 22,000 cases were reported. Dr Chong Chee-Seng, director of environmental epidemiology and toxicology at the Environmental Health Institute, said the outbreak “really spurred us in terms of research.”

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That really spurred us in terms of research.

The project releases specially bred male Aedes aegypti mosquitoes carrying the naturally occurring Wolbachia bacterium. When they mate with wild females, the resulting eggs do not hatch, gradually suppressing the mosquito population. Only males are released, and they do not bite. Dr Chong said the message that “male mosquitoes don’t bite” became central to winning residents’ acceptance, after years of public advice focused on preventing mosquitoes from breeding.

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The only question is, if we release mosquitoes, can people accept it?

The bacterium occurs naturally in more than 60% of insect species, including butterflies. At the production facility, mosquito eggs hatch in water and develop into larvae and then pupae. Workers sort the males from the females, while adult mosquitoes remain together in cages to produce eggs for the next generation. The cycle takes about a week.

A decade into the project, officials report that Aedes aegypti populations at release sites have dropped by 80% to 90%. They say this corresponds to a reduction of about 70% in dengue transmission.

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Male mosquitoes don’t bite.