FEHD Intensifies Mosquito Control Amid Prolonged Rainfall in Hong Kong

2025-08-06 21:16 Last Updated At：21:28

FEHD collaborates with relevant departments and stakeholders to strengthen post-rain mosquito control and elimination efforts

In response to the prolonged rain on recent days, the Food and Environmental Hygiene Department (FEHD) will continue to collaborate with relevant departments and stakeholders to strengthen mosquito control and elimination efforts. These include removing stagnant water at construction sites and locations with higher mosquito infestation risks, and eliminating adult mosquitoes. The FEHD also urges members of the public and stakeholders, including property management companies and construction sites, to step up inspections and remove stagnant water in their areas to prevent and control mosquito infestation.

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A spokesman for the FEHD said today (August 6) that, repeated heavy rain may wash away pesticides previously applied in the environment and lead to increased water accumulation. Sites where stagnant water and mosquito breeding were once detected may now have shifted. The FEHD is therefore continuing to work with relevant departments and stakeholders to intensify inspections of high-risk locations prone to water accumulation after heavy rains, including construction sites, works sites and spots that have previously recorded high gravidtrap indices. If stagnant water is found to be a potential mosquito breeding ground, it will be removed immediately. Larvicides such as temephos sand granules will be applied to stagnant water that cannot be cleared, and ultra-low volume fogging operations will be carried out in adult mosquito habitats such as densely wooded areas, dark and secluded places, and abandoned structures to eliminate adult mosquitoes.

The FEHD has also collaborated with District Councils, District Offices, and relevant stakeholders to strengthen publicity and education efforts, and to conduct joint clean-up operations targeting mosquito breeding blackspots (such as public areas in "three-nil" buildings) in the districts to further curb mosquito breeding.

August is Hong Kong's rainy season, and hot, rainy weather fosters rapid mosquito breeding. The FEHD reminds members of the public and stakeholders to continue mosquito prevention efforts and remove stagnant water to reduce mosquito breeding opportunities. Effective mosquito control requires the collaborative efforts of the public and all sectors.

Members of the public should remain vigilant and promptly take special mosquito prevention and control measures at home and in other environments during heavy rain. These measures include:

Check home environment (outdoor and open areas in particular) for stagnant water, which can easily lead to mosquito problems;

Check household items (those placed in outdoor and open areas in particular), such as refuse containers, vases, air conditioner drip trays, and laundry racks, to prevent stagnant water;

Cover water containers such as buckets and basins; and

Check and clean areas prone to stagnant water at least weekly to prevent mosquito breeding.

Person-in-charge of property management companies and schools should take the following measures to prevent mosquito breeding caused by rain:

Inspect common areas of the property/school for large areas of stagnant water, and arrange for the removal of stagnant water and filling of sunken areas;

Check drain gates and outlets for blockage by dead leaves or rubbish, and keep drains clear;

Check umbrella stands, umbrella tubes, and air-conditioner drip trays to prevent stagnant water;

Properly dispose of water containers and place rubbish in covered bins;

After heavy rain, manhole keyhole fillers, adhesive tape, or plastic keyhole covers may be washed away by rainwater. These should be refilled with sand or covered with plastic keyhole covers or adhesive tape; and

Inspect green areas including flower pots, flower beds or gardening areas, and remove stagnant water to prevent mosquito breeding.

Construction site managers should also conduct early assessments and implement effective measures to prevent mosquito infestations. These measures include:

Inspect the construction site during and after heavy rain to ensure there is no stagnant water that could breed mosquitoes. If large areas of stagnant water are present, they should be emptied as soon as possible using tools like a pump;

Check water barriers or other items (such as canvas for covering) for stagnant water. Bamboo scaffolding should have its end caps sealed with fine sand or drilled through to prevent water accumulation; and

If stagnant water is difficult to remove, apply larvicides such as temephos sand granules as appropriate.

Members of the public may refer to the FEHD's webpage on mosquito prevention and control (www.fehd.gov.hk/english/pestcontrol/risk-pest-mosquito.html), and should constantly pay attention to the information regarding chikungunya fever released by the Centre for Health Protection of the Department of Health. The public should call 1823 in case of mosquito problems.

FEHD Releases May Gravidtrap Indexes for Aedes Albopictus, Highlights Areas of Concern and Control Measures.

FEHD releases fourth batch of gravidtrap indexes for Aedes albopictus in May

The Food and Environmental Hygiene Department (FEHD) today (May 21) released the fourth batch of gravidtrap indexes and density indexes for Aedes albopictus in May, covering 12 survey areas, as follows:

District

Survey Area

May 2026

First Phase Gravidtrap Index

First Phase Density Index

Eastern

Shau Kei Wan and Sai Wan Ho

9.1%

1.4

Islands

Tung Chung

2.0%

1.0

Kowloon City

Hung Hom and To Kwa Wan

6.7%

1.5

Tai Po

Tai Po East

2.2%

2.0

Tai Po West

15.5%

1.0

Tuen Mun

Tuen Mun South

9.1%

1.4

District

Survey Area

May 2026

Area Gravidtrap Index

Area Density Index

Central and Western

Kennedy Town and Shek Tong Tsui

16.8%

1.3

Eastern

Chai Wan

15.4%

1.0

North Point and Quarry Bay

18.9%

1.4

Southern

Aberdeen and Ap Lei Chau

20.8%

1.7

Sha Tin

Sha Tin Town Centre and Fo Tan

18.3%

1.4

Tsuen Wan

Tsuen Wan Town

6.9%

2.3

The fourth batch of gravidtrap indexes for Aedes albopictus in May includes First Phase Gravidtrap Indexes covering six survey areas and Area Gravidtrap Indexes covering six survey areas. Among which, six survey areas recorded gravidtrap indexes above 10 per cent, while Aberdeen and Ap Lei Chau in Southern District recorded a gravidtrap index above 20 per cent. Meanwhile, the gravidtrap indexes of six survey areas, namely Kennedy Town and Shek Tong Tsui in Central and Western District; North Point and Quarry Bay in Eastern District; Shau Kei Wan and Sai Wan Ho in Eastern District; Aberdeen and Ap Lei Chau in Southern District; Tai Po East in Tai Po District; and Tuen Mun South in Tuen Mun District, have recorded a decrease as compared to the indexes recorded in the last survey period, reflecting the progress of relevant mosquito control work.

With reference to the data from the past few years, the gravidtrap indexes start to rise from April or May every year. The actual timing and extent of the rise are affected by factors like weather conditions and rainfall. The average temperature and rainfall recorded in April this year were higher than those in the same period last year, creating favourable conditions for mosquito growth and breeding. As a result, the rise in gravidtrap indexes occurred earlier this year. With the increase in rainfall in May, the gravidtrap indexes are expected to rise further.

For survey areas which recorded indexes exceeding 10 per cent, in accordance with the mechanism implemented by the FEHD in response to the chikungunya fever (CF) situation (i.e. strengthening mosquito control work in areas with a gravidtrap index between 10 per cent and 20 per cent, instead of 20 per cent or above under the original mechanism), the FEHD is collaborating with relevant departments and stakeholders to identify locations with high mosquito infestations and carry out intensive and targeted mosquito control measures. The FEHD has initiated two prosecutions against the relevant construction site contractors following the discovery of mosquito breeding at construction sites in Tai Po District and Southern District. Moreover, following the discovery of stagnant water or stagnant water containers in a park, a construction site, a private housing estate, a clinic and a private premises in Tai Po District, Central and Western District, as well as Southern District, the FEHD has issued five statutory notices to the responsible persons-in-charge, requiring the clearance of such items within a specified timeframe. The FEHD, the relevant departments and stakeholders are following up on the mosquito control work, and will also organise exhibitions, distribute leaflets and posters, and notify residential estates that have subscribed to the gravidtrap Rapid Alert System, advising property management agents and residents to stay vigilant and work together in taking mosquito prevention and elimination measures. In addition, the FEHD will strengthen the monitoring of the gravidtrap index in the areas to review the effectiveness of the mosquito control work.

Public participation is crucial to the effective control of mosquito problems. The FEHD appeals to members of the public to continue to work together in strengthening personal mosquito control measures, including:

tidy up their premises and check for any accumulation of water inside the premises;

remove all unnecessary water collections and eliminate the sources;

check household items (those placed in outdoor and open areas in particular), such as refuse containers, vases, air conditioner drip trays, and laundry racks to prevent stagnant water;

change water in flower vases and scrub their inner surfaces thoroughly, and remove water in saucers under potted plants at least once a week;

properly cover all containers that hold water to prevent mosquitoes from accessing the water;

properly dispose of articles that can contain water, such as disposable meal boxes and empty cans; and

scrub drains and surface sewers with alkaline detergent at least once a week to remove any mosquito eggs.

Starting in August 2025, following the completion of the surveillance of individual survey areas, and once the latest gravidtrap index and the density index are available, the FEHD has been disseminating relevant information through press releases, its website and social media. It aims to allow members of the public to quickly grasp the mosquito infestation situation and strengthen mosquito control efforts, thereby reducing the risk of CF transmission.

Following recommendations from the World Health Organization and taking into account the local situation in Hong Kong, the FEHD sets up gravidtraps in districts where mosquito-borne diseases have been recorded in the past, as well as in densely populated places such as housing estates, hospitals and schools to monitor the breeding and distribution of Aedes albopictus mosquitoes, which can transmit CF and dengue fever. At present, the FEHD has set up gravidtraps in 62 survey areas of the community, with a surveillance period of two weeks. During the surveillance period, the FEHD will collect the gravidtraps once a week. After the first week of surveillance, the FEHD will immediately examine the glue boards inside the retrieved gravidtraps for the presence of adult Aedine mosquitoes to compile the Gravidtrap Index (First Phase) and Density Index (First Phase). At the end of the second week of surveillance, the FEHD will instantly check the glue boards for the presence of adult Aedine mosquitoes. Data from the two weeks of surveillance will be combined to obtain the Area Gravidtrap Index and the Area Density Index. The gravidtrap and density indexes for Aedes albopictus in different survey areas, as well as information on mosquito prevention and control measures, are available on the department's webpage (www.fehd.gov.hk/english/pestcontrol/dengue_fever/Dengue_Fever_Gravidtrap_Index_Update.html#).

FEHD Intensifies Mosquito Control Amid Prolonged Rainfall in Hong Kong

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