Local Vector Biology

Aedes albopictus

  1. Eggs can withstand drought very well
  2. Breed in small containers such as cans, discarded tyres, tree holes, rock pools and bamboo ends holding small amount of water
  3. Adults rest in shrubby area
  4. Adult has a white stripe on the dorsal surface of thorax and bands on legs
  5. Although exophilic, adults may also enter into houses
  6. Day biter (Peak : within 2 hours after dawn and before sunset)
  7. Weak flier (about 100m)
  8. Vector of dengue fever

Vector Surveillance

Gravidtrap

Since 2000, the Food and Environmental Hygiene Department (FEHD) has been using Oviposition Trap (Ovitrap) to detect the presence of adult Aedine mosquitoes. Tools and methodology of dengue vector surveillance is reviewed from time to time and starting from April 2020, a new tool, Gravidtrap has been adopted to replace ovitrap for monitoring the dengue vector of Aedine mosquitoes. The Gravidtrap is a simple device made of a black plastic container of approximately 600ml with a glue board placed inside. It is covered by a black lid with openings and a raised grey cover.

Oviposition Trap (Ovitrap)

Gravidtrap Index

To study the distribution of Aedes albopictus, Gravidtraps are set in selected areas throughout the territory for monitoring the breeding of these mosquitoes. The percentage of the Gravidtraps found positive with breeding of these mosquitoes gives the Gravidtrap Index for Aedes albopictus. The value of Gravidtrap Index for Aedes albopictus indicates the extensiveness of the breeding of the vectors.

Scope of Survey

At present, there are a total of 64 survey areas selected for the vector surveillance throughout the territory and the following four different indices will be enumerated:

  1. Area Gravidtrap Index for Aedes albopictus (AGI),
  2. Area Density Index for Aedes albopictus (ADI),
  3. Monthly Gravidtrap Index for Aedes albopictus (MGI), and
  4. Monthly Density Index for Aedes albopictus (MDI).

The AGI and ADI indicate the extensiveness of the distribution and density of Aedine mosquitoes respectively in that particular survey area, while the MGI and MDI are enumerated by pooling together all AGIs and ADIs of the same month reflecting the territory-wide situation of Aedes albopictus.

In addition to the areas in the community, surveys of Aedes albopictus are also carried out to cover all major port areas. The following two different groups of indices will be enumerated:

  1. Port / Port Monthly Gravidtrap Index for Aedes albopictus (PGI/PMGI), and
  2. Port / Port Monthly Density Index for Aedes albopictus (PDI/PMDI).

The Port Gravidtrap Index for Aedes albopictus (PGI) indicates the extensiveness of the distribution of Aedine mosquitoes in a particular group of port areas. The Port Monthly Gravidtrap Index for Aedes albopictus (PMGI) is enumerated by pooling together all PGIs of the same month, which reflects the overall degree of occurrence of Aedes albopictus in port areas. Another index, the Port Density Index for Aedes albopictus (PDI) indicates the density of Aedes albopictus in positive traps in a particular group of port areas. The Port Monthly Density Index for Aedes albopictus (PMDI) is enumerated by pooling together all PDIs of the same month, which denotes the overall density of Aedes albopictus in locales detected with Aedine mosquito activities in port areas.

Gravidtrap only detects activities of Aedine mosquitoes in the area where it is set. It cannot be used for detecting activities of other species of mosquitoes (such as Culex and Anopheline mosquitoes). The Gravidtrap Index for Aedes albopictus of an area reflects the extensiveness of the distribution of Aedine mosquitoes and the Density Index for Aedes albopictus of an area reflects the density of Aedes albopictus in the relevant surveillance area during the two weeks of surveillance. Apart from making reference to the relevant Gravidtrap Index and Density Index for Aedes albopictus, parties concerned should take into account other factors (such as the findings and reports on mosquito problem received) in planning and implementing their mosquito prevention and control work.

Survey Mechanism

The period for setting Gravidtraps in the survey areas is two weeks. During the survey period, the Gravidtraps are collected on a weekly basis. At the end of the first week of surveillance, all the Gravidtraps are retrieved and another batch of Gravidtraps is set at the same location for surveillance for the second week. The glue boards inside the retrieved Gravidtraps are immediately examined for the presence of adult Aedine mosquitoes (“Aedes-positive”) for the purpose of compiling the Gravidtrap Index (First Phase) and Density Index (First Phase). At the end of the second week of surveillance, all the Gravidtraps are retrieved and instantly checked for the presence of adult Aedine mosquitoes (“Aedes-positive”) on the glue boards. Data of the two weeks’ surveillance will be combined to obtain the Area Gravidtrap Index (AGI) and Area Density Index (ADI).

FEHD will notify its District Environmental Hygiene Offices and other relevant government departments of the Gravidtrap Indices and Density Indices of various phases once the figures are available, so that they can promptly carry out targeted mosquito prevention and control work. To facilitate public access to the latest survey data, FEHD will announce the phased indices for Aedes albopictus for each of the surveyed areas on the FEHD webpage. Corresponding mosquito prevention and control measures can be taken by the public in a more expeditious manner so as to prevent the spread of dengue fever.

The Gravidtrap Index and Density Index for Aedes albopictus of each surveyed area are released in two phases. Figures released in the first phases are phased indices and the second phase indices represent the AGI and ADI of the surveyed area in that month.

Monthly Ovitrap Index

Monthly Ovitrap Index

Level of Index

Gravidtrap Index

The Gravidtrap Index for Aedes albopictus is divided into four levels, reflecting the distribution level of the Aedes albopictus. Level 1 (less than 5 per cent) indicates that distribution of Aedes albopictus is not extensive in the area surveyed. Level 2 (5 per cent to less than 20 per cent) indicates that distribution of Aedes albopictus is fairly extensive in the area surveyed. Level 3 (20 per cent to less than 40 per cent) indicates that distribution of Aedes albopictus is extensive in the area surveyed. Level 4 (40 per cent or above) indicates that distribution of Aedes albopictus is very extensive in the area surveyed. Specific preventive and control measures will be initiated accordingly. Management of housing estates, hospitals, schools, construction sites and other venues or properties are also advised to take specific measures to contain mosquito problems in their own properties. The four levels of Gravidtrap Index for Aedes albopictus and actions to be taken by the management are listed in the following table.

Level Gravidtrap Index for Aedes albopictus Actions to be taken
1 G.I. < 5%
(Distribution of Aedes albopictus in the survey area is not extensive)
  • Closely monitor the hygienic condition to prevent breeding of mosquitoes;
  • Conduct weekly inspection to identify breeding / potential breeding places and eliminate such places as far as possible.
  • Public are advised to check and eliminate any possible breeding places within their premises at a frequency not less than once a week (Please go to Advice to the Public for details)
2 5% ≤ G.I. < 20%
(Distribution of Aedes albopictus in the survey area is fairly extensive)
3 20% ≤ G.I. < 40%
(Distribution of Aedes albopictus in the survey area is extensive)
  • To conduct special operations in addition to the regular weekly program to eliminate all breeding / potential breeding places;
  • Private pest control contractor might be employed to control the mosquito problem. Other control measures by using larvicides or adulticides might be feasible.
4 G.I. ≥ 40%
(Distribution of Aedes albopictus in the survey area is very extensive)

Density Index

With the adoption of Gravidtraps since April 2020, a new index called the Density Index (DI) is also recorded in each survey area.  It is denoted as Area Density Index (ADI) which is enumerated by dividing the number of adult Aedes by the total number of Aedes positive Gravidtraps during the survey period.  The minimum value of the index is one.

The Density Index for Aedes albopictus is divided into three levels, reflecting the abundancy of Aedes albopictus.  Level 1 (1 to 1.5) indicates that mosquito is not abundant in the locations with positive Gravidtraps.  Level 2 (1.6 to 2.4) indicates that mosquito is slightly abundant in the locations with positive Gravidtraps.  Level 3 (2.5 or above) indicates that mosquito is abundant in the locations with positive Gravidtraps.  Specific preventive and control measures will be initiated accordingly.  Management of housing estates, hospitals, schools, construction sites and other venues or properties will also be advised to take specific measures to contain mosquito problems in their own properties.  The three levels of DI and actions to be taken by the management are listed in the following table. 

Level Density Index for Aedes albopictus Actions to be taken
1

1 ≤ D.I. ≤ 1.5
(Mosquito is not abundant in the locations with positive Gravidtraps)

  • Closely monitor the hygienic condition to prevent breeding of mosquitoes;
  • Conduct weekly inspection to identify breeding / potential breeding places and eliminate such places as far as possible.
  • Public are advised to check and eliminate any possible breeding places within their premises at a frequency not less than once a week (Please go to Advice to the Public for details)
2

1.6 ≤ D.I. ≤ 2.4
(Mosquito is slightly abundant in the locations with positive Gravidtraps)

  • Conduct special operations in addition to the regular weekly inspection to eliminate all breeding / potential breeding places at location with high mosquito density
3

D.I. ≥ 2.5
(Mosquito is abundant in the locations with positive Gravidtraps)

  • Private pest control contractor may be employed to control the mosquito problem in target locations. Other control measures by using larvicides or adulticides may also be taken.

Public should refer to the “Action to be taken” for AGI as primary reference.  If both indices are of similar levels, their actions are also similar.  However, if the AGI is low, e.g. Level 1 or Level 2, but level of ADI is high, e.g. Level 3, public should carry out actions for corresponding level of AGIs and supplement with actions for higher level of ADI, e.g. fogging, in locations with high mosquito density.

Information of Survey Area in the Community

Latest Index Information

The phased Gravidtrap Indices and Density Indices for Aedes albopictus for each surveyed area in March 2023 are provided below:

Hong Kong Island

District

Survey area

First Phase Gravidtrap Index First Phase Density Index Area Gravidtrap Index Area Density Index
Central/Western Central and Admiralty 0.0% N/A 0.0% N/A
Sheung Wan and Sai Ying Pun 0.0% N/A
Sai Wan 0.0% N/A
Eastern Chai Wan West 0.0% N/A 0.0% N/A
Shau Kei Wan and Sai Wan Ho 0.0% N/A 0.9% 1.0
North Point 0.0% N/A 0.0% N/A
Southern Aberdeen and Ap Lei Chau 0.0% N/A 0.0% N/A
Pokfulam 0.0% N/A 2.6% 1.0
Deep Water Bay and Repulse Bay 1.7% 1.0 0.8% 1.0
Wan Chai Tin Hau 2.0% 1.0 1.0% 1.0
Wan Chai North 0.0% N/A 0.0% N/A
Happy Valley 0.0% N/A 0.0% N/A
Islands
Islands Cheung Chau South
(Formerly: Cheung Chau)
0.0% N/A
Cheung Chau North 0.0% N/A
Tung Chung
Kowloon
District Survey area First Phase Gravidtrap Index First Phase Density Index Area Gravidtrap Index Area Density Index
Yau Tsim Tsim Sha Tsui 0.0% N/A
Tsim Sha Tsui East 0.0% N/A 0.0% N/A
Mong Kok Mong Kok 0.0% N/A 0.0% N/A
Sham Shui Po Cheung Sha Wan
Lai Chi Kok
Sham Shui Po East
Kowloon City Ho Man Tin 0.0% N/A 0.0% N/A
Kowloon City North 0.0% N/A
Hung Hom 0.0% N/A
Lok Fu West 0.0% N/A
Kai Tak North
Wong Tai Sin Wong Tai Sin Central 0.0% N/A 0.0% N/A
Wong Tai Sin West 0.0% N/A 0.0% N/A
Diamond Hill 0.0% N/A 0.0% N/A
Ngau Chi Wan 0.0% N/A 0.0% N/A
Kwun Tong Kwun Tong Central 0.0% N/A
Lam Tin 0.0% N/A
Yau Tong
Kowloon Bay 0.0% N/A
New Territories
District Survey area First Phase Gravidtrap Index First Phase Density Index Area Gravidtrap Index Area Density Index
Sai Kung Tseung Kwan O West
(Formerly: Tseung Kwan O South)
0.0% N/A 0.0% N/A
Tseung Kwan O East
Tseung Kwan O North
Sai Kung Town 0.0% N/A
Ngau Liu and Muk Min Shan 0.0% N/A
Sha Tin Tai Wai 1.6% 1.0 1.6% 1.0
Sha Tin East 0.0% N/A 0.0% N/A
Ma On Shan 0.0% N/A 0.0% N/A
Sha Tin Town Centre and Fo Tan 0.0% N/A 0.0% N/A
Tai Po Tai Po West 0.0% N/A 0.9% 1.0
Tai Po East 0.0% N/A 0.0% N/A
North Fanling 0.0%   N/A
Sheung Shui 0.0% N/A 0.0% N/A
Yuen Long Tin Shui Wai 0.0% N/A
Yuen Kong
Yuen Long Town 0.0% N/A 0.0% N/A
Ki Lun Shan 0.0% N/A
Sung Shan 0.0% N/A
Tuen Mun Tuen Mun North 0.0% N/A 0.0% N/A
Tuen Mun South 0.0% N/A 0.0% N/A
Tuen Mun West 2.2% 1.0 1.1% 1.0
So Kwun Wat 0.0% N/A 0.0% N/A
Tseun Wan Tsuen Wan Town 0.0% N/A
Tsuen Wan West 0.0% N/A
Ma Wan
Sheung Kwai Chung 0.0% N/A
Kwai Tsing Kwai Chung 0.0% N/A
Lai King 0.0% N/A
Tsing Yi South 0.0% N/A
Tsing Yi North 0.0% N/A

Index value remarks:

Colour Gravidtrap Index Density Index
Green:Level I Gravidtrap Index < 5.0% [indicates that the distribution of Aedes albopictus is not extensive] 1.0 ≤ Density Index ≤ 1.5 [Aedes albopictus is not abundant in the locations with positive Gravidtraps]
Yellow:Level II 5.0% ≤ Gravidtrap Index <20 .0% [indicates that the distribution of Aedes albopictus is fairly extensive] 1.6 ≤ Density Index ≤ 2.4 [Aedes albopictus is slightly abundant in the locations with positive Gravidtraps]
Red:Level III 20.0% ≤ Gravidtrap Index  <40 .0% [indicates that the distribution of Aedes albopictus  is extensive]

Density Index ≥ 2.5 [Aedes albopictus is abundant in the locations with positive Gravidtraps]

Purple:Level IV Gravidtrap Index ≥40.0%  [indicates that the distribution of Aedes albopictus  is very extensive]

Brief of Gravidtrap Indices and Density Indices in February 2023

The monthly Gravidtrap index for Aedes albopictus in February was 0.3 per cent. The index in February remained at Level 1 at its lowest, indicating that distribution of Aedes albopictus in the areas surveyed was not extensive.

All the 64 survey areas were recorded with a Gravidtrap index lower than the alert level of 20 per cent. Moreover, the monthly density index for Aedes albopictus in February remained at 1, which represented that an average of one Aedes albopictus adult was found in the Aedes-positive Gravidtraps, indicating that the number of adult Aedes albopictus was not abundant in the survey areas.

Record of Indices in 2023

Area Gravidtrap Indices and Density Indices for Aedes albopictus for the 64 survey areas in 2023 are provided below:

Hong Kong Island (Map)
District Survey Area Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Central/Western Central and Admiralty AGI 0.0% 0.0% 0.0%
ADI N/A N/A N/A
Sheung Wan and Sai Ying Pun AGI 0.0% 0.0%
ADI N/A N/A
Sai Wan AGI 0.0% 0.0%
ADI N/A N/A
Eastern Chai Wan West AGI 0.0% 0.0% 0.0%
ADI N/A N/A N/A

Shau Kei Wan and Sai Wan Ho

AGI 4.4% 0.0% 0.9%
ADI 1.0 N/A 1.0
North Point AGI 0.0% 0.0% 0.0%
ADI N/A N/A N/A
Southern Aberdeen and Ap Lei Chau AGI 0.0% 0.0% 0.0%
ADI N/A N/A N/A
Pokfulam AGI 0.0% 0.9% 2.6%
ADI N/A 1.0 1.0
Deep Water Bay and Repulse Bay AGI 0.0% 0.0% 0.8%
ADI N/A N/A 1.0
Wanchai Tin Hau AGI 0.0% 0.0% 1.0%
ADI N/A N/A 1.0
Wan Chai North AGI 0.0% 0.0% 0.0%
ADI N/A N/A N/A
Happy Valley AGI 0.0% 0.0% 0.0%
ADI N/A N/A N/A
Islands (Map)
District Survey Area Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Islands Cheung Chau South
(Formerly: Cheung Chau)
AGI 0.0% 0.0%
ADI N/A N/A
Cheung Chau North AGI 0.0% 0.0%
ADI N/A N/A
Tung Chung AGI 0.0% 0.0%
ADI N/A N/A
Kowloon (Map)
District Survey Area Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Yau Tsim Tsim Sha Tsui AGI 0.0% 0.0%
ADI N/A N/A
Tsim Sha Tsui East AGI 0.0% 0.0% 0.0%
ADI N/A N/A N/A
Mong Kok Mong Kok AGI 0.0% 0.0% 0.0%
ADI N/A N/A N/A
Sham Shui Po Cheung Sha Wan AGI 0.0% 0.0%
ADI N/A N/A
Lai Chi Kok AGI 0.0% 0.0%
ADI N/A N/A
Sham Shui Po East AGI 0.0% 0.0%
ADI N/A N/A
Kowloon City Ho Man Tin AGI 0.0% 0.0% 0.0%
ADI N/A N/A N/A
Kowloon City North AGI 0.0% 0.0%
ADI N/A N/A
Hung Hom AGI 0.9% 0.0%
ADI 1.0 N/A
Lok Fu West AGI 0.0% 0.0%
ADI N/A N/A
Kai Tak North AGI 3.8% 1.4%
ADI 1.0 1.0
Wong Tai Sin Wong Tai Sin Central AGI 0.0% 0.0% 0.0%
ADI N/A N/A N/A
Wong Tai Sin West AGI 0.0% 0.0% 0.0%
ADI N/A N/A N/A
Diamond Hill AGI 0.0% 0.0% 0.0%
ADI N/A N/A N/A
Ngau Chi Wan AGI 0.0% 0.0% 0.0%
ADI N/A N/A N/A
Kwun Tong Kwun Tong Central AGI 0.0% 0.0%
ADI N/A N/A
Lam Tin AGI 0.0% 0.0%
ADI N/A N/A
Yau Tong AGI 0.0% 0.0%
ADI N/A N/A
Kowloon Bay AGI 0.0% 0.0%
ADI N/A N/A
New Territories (Map)
District Survey Area Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Sai Kung Tseung Kwan O West
(Formerly: Tseung Kwan O South)
AGI 0.0% 0.0% 0.0%
ADI N/A N/A N/A
Tseung Kwan O East AGI 0.0% 0.9%
ADI N/A 1.0
Tseung Kwan O North AGI 0.0% 0.0%
ADI N/A N/A
Sai Kung Town AGI 0.0% 0.0%
ADI N/A N/A
Ngau Liu and Muk Min Shan AGI 0.0% 2.1%
ADI N/A 1.0
Sha Tin Tai Wai AGI 0.0% 0.8% 1.6%
ADI N/A 1.0 1.0
Sha Tin East AGI 0.0% 0.0% 0.0%
ADI N/A N/A N/A
Ma On Shan AGI 1.7% 2.5% 0.0%
ADI 1.0 1.0 N/A
Sha Tin Town Centre and Fo Tan AGI 0.0% 1.9% 0.0%
ADI N/A 1.0 N/A
Tai Po Tai Po West AGI 0.0% 0.0% 0.9%
ADI N/A N/A 1.0
Tai Po East AGI 0.0% 0.0% 0.0%
ADI N/A N/A N/A
North Fanling AGI 0.0% 0.0%
ADI N/A N/A
Sheung Shui AGI 1.8% 1.7% 0.0%
ADI 1.0 1.0 N/A
Yuen Long Tin Shui Wai AGI 0.0% 0.0%
ADI N/A N/A
Yuen Kong AGI 0.0% 0.0%
ADI N/A N/A
Yuen Long Town AGI 0.0% 1.0% 0.0%
ADI N/A 1.0 N/A
Ki Lun Shan AGI 0.0% 2.0%
ADI N/A 1.0
Sung Shan AGI 0.0% 0.0%
ADI N/A N/A
Tuen Mun Tuen Mun North AGI 0.0% 0.0% 0.0%
ADI N/A N/A N/A
Tuen Mun South AGI 0.0% 0.0% 0.0%
ADI N/A N/A N/A
Tuen Mun West AGI 2.1% 0.0% 1.1%
ADI 1.0 N/A 1.0
So Kwun Wat AGI 0.9% 0.0% 0.0%
ADI 1.0 N/A N/A
Tsuen Wan Tsuen Wan Town AGI 0.0% 0.0%
ADI N/A N/A
Tseun Wan West AGI 0.0% 0.9%
ADI N/A 1.0
Ma Wan AGI 2.0% 4.2%
ADI 1.0 1.0
Sheung Kwai Chung AGI 0.0% 0.0%
ADI N/A N/A
Kwai Tsing Kwai Chung AGI 0.0% 0.0%
ADI N/A N/A
Lai King AGI 0.0% 0.0%
ADI N/A N/A
Tsing Yi South AGI 0.0% 0.0%
ADI N/A N/A
Tsing Yi North AGI 0.0% 0.9%
ADI N/A 1.0

Index value remarks:

Colour Gravidtrap Index Density Index
Green:Level I Gravidtrap Index < 5.0% [indicates that the distribution of Aedes albopictus is not extensive] 1.0 ≤ Density Index ≤ 1.5 [Aedes albopictus is not abundant in the locations with positive Gravidtraps]
Yellow:Level II 5.0% ≤ Gravidtrap Index <20 .0% [indicates that the distribution of Aedes albopictus is fairly extensive] 1.6 ≤ Density Index ≤ 2.4 [Aedes albopictus is slightly abundant in the locations with positive Gravidtraps]
Red:Level III 20.0% ≤ Gravidtrap Index  <40 .0% [indicates that the distribution of Aedes albopictus  is extensive]

Density Index ≥ 2.5 [Aedes albopictus is abundant in the locations with positive Gravidtraps]

Purple:Level IV Gravidtrap Index ≥40.0%  [indicates that the distribution of Aedes albopictus  is very extensive]

Number of areas in respective levels of Survey Area Gravidtrap Indices in 2023 are provided below:

Number of survey areas recorded with
respective Index Level 
Total number of survey areas Top 5 survey areas at level 3 Top 5 survey areas at level 4
Level 1 Level 2 Level 3 Level 4
0%-<5% 5%-<20% 20%-<40% ≥40%
Jan 64 0 0 0 64 Nil Nil
Feb 64 0 0 0 64 Nil Nil

Comparision of Monthly Gravidtrap Index and Density Index for Aedes albopictus in 2022 and 2023 are provided below:

The comparison of Monthly Gravidtrap Index and Monthly Density Index for Aedes albopictus between 2020 and 2021

The comparison of Monthly Gravidtrap Index and Monthly Density Index for Aedes albopictus between 2020 and 2021

Information of Major Port Areas

The Port Monthly Gravidtrap and the Port Monthly Density Index for Aedes albopictus for February 2023 are 0.02% and 1.0 respectively.

Port Gravidtrap Indices and Port Density Indices for Aedes albopictus in 2023 are provided below:

Port areas (Map)
Port Area Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Hong Kong International Airport PGI 0.0% 0.0%
PDI N/A N/A
Cross Boundary Check Points on Land PGI 0.2% 0.0%
PDI 1.0 N/A
Private Cargo Working Areas PGI 0.0% 0.0%
PDI N/A N/A
Cross Boundary Ferry Terminals PGI 0.0% 0.0%
PDI N/A N/A
Container Terminals PGI 0.0% 0.0%
PDI N/A N/A
Public Cargo Working Areas PGI 0.0% 0.2%
PDI N/A 1.0

Index value remarks:

Colour Gravidtrap Index Density Index
Green:Level I Gravidtrap Index < 5.0% [indicates that the distribution of Aedes albopictus is not extensive] 1.0 ≤ Density Index ≤ 1.5 [Aedes albopictus is not abundant in the locations with positive Gravidtraps]
Yellow:Level II 5.0% ≤ Gravidtrap Index <20 .0% [indicates that the distribution of Aedes albopictus is fairly extensive] 1.6 ≤ Density Index ≤ 2.4 [Aedes albopictus is slightly abundant in the locations with positive Gravidtraps]
Red:Level III 20.0% ≤ Gravidtrap Index  <40 .0% [indicates that the distribution of Aedes albopictus  is extensive]

Density Index ≥ 2.5 [Aedes albopictus is abundant in the locations with positive Gravidtraps]

Purple:Level IV Gravidtrap Index ≥40.0%  [indicates that the distribution of Aedes albopictus  is very extensive]

Historical information in respect of  Ovitrap indices, Gravidtrap Indices and Density Indices 

Please click here for the Monthly Ovitrap Index, Gravidtrap Index and Density Index for Aedes albopictus from 2013 to 2022.

Please click here for a graph of comparison of Monthly Ovitrap Index for Aedes albopictus: 2010 to 2019 and 2020.

Please click here for a graph of comparison of Monthly Gravidtrap Index for Aedes albopictus: 2020 to 2021 and 2022.

Please click here for a graph of comparison of Monthly Density Index for Aedes albopictus: 2020 to 2021 and 2022.

Please click here for the Port Monthly Ovitrap Index, Gravidtrap Index and Density Index for Aedes albopictus from 2013 to 2022.

Preventive Measures

Advice on mosquito control and prevention

Aedes albopictus (白紋伊蚊) is highly prevalent in Hong Kong. It breeds both in urban and rural areas and their breeding sites can be artificial receptacles like cans, lunch boxes, discarded tyres, clogged surface channels, containers; and naturally occurring tree holes, bamboo stumps and leaf axils.

Killing of mosquito larvae

Prevention is better than cure. As the mosquitoes have to breed in water, it is more effective and efficient to control mosquito at source at its aquatic stage. Pesticide should only be used for killing of mosquito in its breeding place or preventing its breeding if the breeding sources or potential breeding grounds are inaccessible or could not be eliminated for the time being. The followings must be noted for killing mosquito larvae:

  1. Larvicidal oil or larvicide (such as temephos, Bacillus thuringiensis subspecies israelensis etc.) can be applied to stagnant water directly with dosage according to the label instructions.
  2. Higher than required concentration of larvicide or excessive amount of larvicidal oil would not give better result on killing the mosquito larvae.
  3. The pesticides used must have been registered with the Agriculture, Fisheries and Conservation Department.
  4. Depending on the product, larvicide may be applied weekly into the stagnant water until the water has been removed.
  5. Larvicidal oil need not be applied into the stagnant water again if the oil is still present in the water.
  6. Pesticide applicator should put on protective gears including face mask and rubber gloves during pesticide application.

Killing of adult mosquito

Elimination of adult mosquitoes is relatively difficult as compared with that of the larvae. Adult mosquitoes usually disperse from their breeding place and hide in inconspicuous sites. The followings must be noted for killing adult mosquitoes:

Protection against adult mosquitoes

Adult mosquito attacks people for getting blood for laying eggs. The followings have to be noted for getting protection against adult mosquitoes:

  1. Windows and doors could be screened.
  2. Wear long-sleeved clothes and long trousers when going outdoors.
  3. Mosquito bednet could be used when the room is not air-conditioned.
  4. Bodies could be protected from mosquito bite by applying mosquito repellent on the clothes or skin according to label instructions.
  5. Some people may be allergic to insect repellent. Apply small amount of insect repellent to small area of the body to check for any allergic response before using the repellent.

Note: Always read and follow label instructions when using pesticides. Please also refer to the leaflet on Safe Use of Household Pesticides produced by Agriculture, Fisheries and Conservation Department for further information. (Tel. No. 2150 7010, Fax: 2314 2622, e-mail: afcdenq@afcd.gov.hk, Web-site: http://www.afcd.gov.hk). The public can also call the telephone hotline of Food and Environmental Hygiene Department at Tel. No. 2868 0000 for more information on mosquito prevention and control.

Remark on mosquito control

Integrated pest management approach has to be adopted for the prevention and control of mosquito. Elimination of stagnant or/and slow running water is the fundamental and most effective mosquito prevention and control method. Application of chemical including pesticide should be the last resort and temporary measure for killing mosquito larvae. Space spraying against adult mosquitoes by using pesticide should only be carried out when there is an urgent need to reduce the number of adult mosquito such as preventing transmission of mosquito-borne diseases. Ecological impacts have to be taken into consideration for selecting the method(s) for mosquito control.

Advice to Public:

  1. To tidy up their premises and check for any accumulation of water inside their premises;
  2. To remove all unnecessary water collection and eliminate the sources;
  3. To change at least every week the water in flower vases and saucers of potted plants to prevent breeding of mosquitoes. The use of saucers should be avoided whenever possible;
  4. To properly cover all containers that hold water to prevent mosquito from accessing the water;
  5. To properly dispose articles that are able to contain water such as empty lunch boxes, cans and tyres;
  6. To stop storing water along morning walk trails or Government land for irrigation;
  7. To make large holes on tyres used as anti-bumping measure in garage to prevent water trapping or use mark(s) on the parking space to prevent bumping instead.
  8. To contact the district pest control offices or PCAS of FEHD, or pest control companies for assistance in mosquito control or prevention.

Anti-mosquito Measures

Weekly Mosquito Inspection Program

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