Phone-wielding and bare-armed, I follow Scott Edmunds and Mendel Wong to a small park in the Mid-Levels area of Hong Kong Island, where a dengue outbreak occurred last year. We hit the jackpot within five minutes – a swarm of mosquitoes around a tree. Hong Kong’s first local case of dengue fever for 2016 confirmed: 79-year-old victim was frequent zoo visitor With his phone, Wong snaps a picture of one that lands on his arm, as well as the breeding site – a pile of discarded rubbish in the alley nearby. From the picture, we can clearly see the white lines on its legs, the distinctive characteristic of both the tiger mosquito (Aedes albopictus) and yellow fever mosquito (Aedes aegypti). “You don’t necessarily have to let it feed on you. You just need a clear picture of the front of its head,” says Wong. He uploads the picture to Mosquito Alert, an app which taps into the power of citizen science by allowing people to report sightings of mosquitoes and their breeding sites. It contains useful guidelines on how to distinguish between various species of mosquitoes. Once a users has uploaded a picture of a mosquito, they are asked to answer three simple questions about its appearance. A team of volunteers and experts will then validate the pictures, in a process that is still being refined. Mosquito infestation in Hong Kong reaches ‘alert’ level, index shows, prompting fears of dengue and Zika virus transmission The breeding sites of mosquitoes matter because both the tiger mosquito and yellow fever mosquito can spread diseases such as dengue fever, yellow fever, Zika fever and chikungunya (similar to dengue). Of the two species, only the tiger mosquito occurs in Hong Kong. The project was born out of a community-led response to the Zika virus outbreak last year, which was declared a global public health emergency by the World Health Organisation. “There was a big information vacuum and we did not know what was happening,” says Edmunds, a genome sequencing scientist. He joined an international online hackathon at which scientists, researchers and designers proposed different strategies, such as DIY traps and noise weapons to fend off mosquitoes, to tackle the problem. There, Edmunds came across Mosquito Alert, an app and citizen science platform built by a research institute in Spain. “Brilliantly, they made the app open-source as they were encouraging people to adapt it,” says Edmunds. Mosquito menace: why Hong Kong needs to step up the fight against dengue fever Edmunds, joined by Wong, a technology professional, worked with the Spanish researchers to build a Hong Kong version of Mosquito Alert. “Hong Kong is the perfect guinea pig because everybody has a smartphone. We are the most app-driven society in the world,” says Edmunds. The pair localised the app by adding indigenous mosquito species and translating the app into Chinese, so it’s available to the widest number of users possible. It was then tested by students at the Chinese Foundation Secondary School in Siu Sai Wan, at the eastern end of Hong Kong Island. One factor that drives their project is the lack of information about the spread of mosquitoes in Hong Kong. Though the government puts out ovitraps to track tiger mosquitoes, the results collected are not publicly available and their use is restricted by many terms and conditions. “The government does not release the data. And since [ovitraps] are put in random places, you cannot validate the data in any scientific way,” says Edmunds. He notes the contrast with Singapore, which has daily updated maps to show clusters of dengue fever infections and breeding sites. “For Hong Kong, it’s like we’ve gone back 100 years.” Although the Hong Kong app is still in the early stages – the team is trying to scale up and gather more users – the data collected can potentially fill the information gap and compensate for the government’s lacklustre effort at informing the public about mosquito breeding sites. In Spain, where the app is running for its third year and has received more than 8,000 reports of mosquito sightings, the team has a valuable database that has been cited in research articles and at scientific conferences. They have also found that people identify the mosquitoes more accurately over time. Hong Kong is the perfect guinea pig because everybody has a smartphone. We are the most app-driven society in the world Scott Edmunds In February, Edmunds and Wong were invited by the United Nations to Geneva to share the results of their project and take part in a new global initiative called Global Mosquito Alert. It is a platform where scientists and volunteers share strategies for tracking mosquito populations. Edmunds and Wong were the only representatives from Asia, as well as being the only citizen science volunteers among the academics, researchers and organisations at the two-day meeting. They hope their project helps people realise the potential of citizen science and encourage other initiatives. “Everybody on the MTR is playing Candy Crush or whatever the latest game is,” says Edmunds. “If we can just harness a tiny per cent of that energy for looking at mosquitoes [we could not only fill the information gap but help stop the spread of mosquito-borne diseases].” Mosquito Alert is available on Android and iOS.