Biology Public health importance Surveillance Control Prevention Health education

mosquito pests and their control

Biology of mosquito

Characteristics of mosquito:

Life cycle: complete metamorphosis with 4 stages (egg, larva, pupa and adult)

Egg:

Larva:

Pupa:

Adult:

Behaviour :

  1. Mating: Female mosquito of many species mate 1 to 2 days after hatching. Female adults normally mate only once in its life.
  2. Feeding: Normally only female adults feed on animal blood. Male adults feed on plant juice. Some species are anthropophilic and some are zoophilic.
  3. Egg laying: Female mosquito of most species has to get blood meal for the development of eggs. Breeding place can be permanent stagnant water, flowing water, temporary stagnant water or containers.
  4. Resting: Adult mosquito rests near breeding site for a few hours after hatching. Exophilic mosquito also rests indoors for a short period of time before and after feeding.
  5. Dispersion: Adult mosquito disperses for feeding, finding suitable resting sites, mating and laying eggs. It can disperse through flight, air current or vehicles.
  6. Hibernation: Some mosquitoes (for example most species of Anopheles and Culex) hibernate in winter at adult stage. Aedes over winter at egg stage.
  7. Longevity: Generally male mosquitoes only survive one week but the females can live for two to three weeks.

Mosquitoes commonly found in Hong Kong

Among the more than 3000 species found around the World, more than 70 species have been found locally. Some 10 species such as Anopheles sinensis, Anopheles maculatus, Aedes albopictus Culex quinquefasciatus and Culex tritaeniorhynchus are commonly found. The mosquito-borne disease vectors found locally are:

  1. Anopheles jeyporiensis (Photo)
    • Breed in paddy field, waterlogged field and stream
    • Female adults are most active during 23.00p.m. to 2.00a.m.
    • Anthropophilic although it also feeds on animals
    • Local malaria vector
  2. Anopheles minimus (Photo)
    • Breed along slow running, unpolluted stream with diffused sunlight and marginal vegetation
    • Greater larval density in periods from March to April and September to October
    • Feed on human and animals at night but viciously at midnight
    • Adults stay indoors before dawn after feeding
    • Local malaria vector
  3. Aedes togoi (Photo)
    • Breed in large number in pools with semi-saline water along seacoasts
    • Vicious night biter
    • Strong flier
    • Vector of filariasis
  4. Aedes albopictus (Photo)
    • Eggs can withstand drought very well
    • Breed in small containers such as cans, discarded tyres, tree holes, rock pools and bamboo ends holding small amount of water
    • Adults rest in shrubby area
    • Adult has a white stripe on the dorsal surface of thorax and bands on legs. Although exophilic, adults may also enter into houses
    • Day biter
    • Weak flier (about 100m)
    • Vector of dengue fever
  5. Culex quinquefasciatus (Photo)
    • Breed in large number in practically all types of water collections from rainwater holding artificial containers to polluted river
    • Always found in construction sites
    • Each egg raft has about 300 eggs
    • Female adults feed viciously on animals or human at night
    • Strong flier
    • Vector of filariasis
  6. Culex tritaeniorhynchus (Photo)
    • Breed in pool, fishpond, water lodged grass field, slow running stream and ditch
    • Adults are active at night with peak of activities one hour after dark
    • Exophilic but stay indoors before and after feeding on blood
    • Mainly zoophagous but also feed on human
    • Vector of Japanese encephalitis and filariasis

Common local mosquito-borne diseases

New information on Ovitrap Index for Aedes albopictus

Mosquito survey

Malaria vector

To study the distribution of Anopheles. A larval and an adult survey have been conducted locally in order to have detailed information about the growth patterns and distribution of the local malaria vectors.

Dengue fever vector

To study the distribution of Aedes albopictus and Aedes aegypti. Oviposition traps are set in 57 areas for monitoring the breeding of these mosquitoes. The percentage of the oviposition trap found positive with breeding of these mosquitoes gives the Ovitrap Index for Aedes albopictus (Number of the Aedes-positive ovitraps/Total number of ovitraps retrieved from a particular area x 100% = Ovitrap Index for Aedes albopictus). The value of Ovitrap Indexes for Aedes albopictus indicates the extensiveness of the breeding of the vectors.

During the survey period, the ovitraps are collected on a weekly basis.  At the end of the first week of surveillance, all the ovitraps are retrieved and another batch of ovitraps is set at the same location for surveillance for the second week.  The ovitraps retrieved are immediately checked for the presence of larvae or eggs of Aedes albopictus (“Aedes-positive”) for the purpose of compiling the Ovitrap Index (First Phase Ovitrap Index).  They are kept in the laboratory for incubation for a week to allow the undetected eggs to hatch into larvae.  The hatched larvae are examined to confirm if they are Aedes albopictus

At the end of the second week of surveillance, all the ovitraps are retrieved and instantly checked for the presence of larvae or eggs of Aedes albopictus (“Aedes-positive”).  The ovitraps retrieved after the first week of surveillance are re-examined to confirm the total number of the Aedes-positive ovitraps (including those in which larvae have hatched at the laboratory).  The Ovitrap Index (Second Phase Ovitrap Index) is obtained by combining these two sets of data.  The ovitraps retrieved after the second week of surveillance are sent to the laboratory for incubation for one week to allow the undetected eggs to hatch into larvae.  The hatched larvae are examined to confirm if they are Aedes albopictus

When the ovitraps retrieved after the second week of surveillance have been kept in the laboratory for incubation for one week, they are re-examined to confirm the total number of the Aedes-positive ovitraps.  Finally, the verified data of the two weeks of surveillance will be combined to obtain the final Ovitrap Index (Area Ovitrap Index). 

The Department has all along adopted the current survey method to detect the presence of Aedes albopictus and will notify the District Environmental Hygiene Offices and the relevant departments of the Ovitrap Indices of various phases once the figures are available, so that they can promptly carry out targeted mosquito prevention and control work.  To facilitate the public's access to the latest survey data on the ovitraps for Aedes albopictus, the Department has announced the phased Ovitrap Index for Aedes albopictus for each of the surveyed areas on our webpage since September 2018.  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 Ovitrap Index for Aedes albopictus of each surveyed area is released in three phases.  Figures released in the first and second phases are phased indices and the third phase index represents the Area Ovitrap Index of the surveyed area in that month.

Please click here for the phased Ovitrap Index in August 2019.

Remarks: The presence of the dengue fever vector, Aedes albopictus or Aedes aegypti does not indicate transmission of the disease will take place. Transmission of the disease may occur only with the presence of the vector mosquito and infectious person.

Comparison of Monthly Average Ovitrap Index (2000-11 and 2012)

Area Ovitrap Index for Aedes albopictus for all the 57 locations in 2019:

Hong Kong (Map)
District Location Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Central/Western Central and Admiralty 0.0% 0.0% 1.0% 11.5% 12.3% 12.5% 11.7% 3.0%
Sheung Wan & Sai Ying Pun(Formerly: Central, Sheung Wan & Sai Ying Pun) 0.0% 0.0% 0.0% 3.4% 5.0% 7.6% 6.8% 5.9%
Sai Wan 0.0% 0.0% 1.9% 4.7% 10.4% 15.5% 7.7% 8.5%
Eastern Chai Wan West 0.0% 0.0% 0.0% 4.5% 5.4% 13.4% 16.1% 4.6%
Shau Kei Wan & Sai Wan Ho 0.0% 0.0% 0.9% 6.1% 6.9% 18.8% 7.1% 11.7%
North Point 0.0% 0.0% 0.0% 0.0% 2.7% 25.0% 17.8% 6.4%
Southern Aberdeen and Ap Lei Chau 0.0% 0.0% 0.0% 2.9% 6.5% 4.9% 5.8% 4.6%
Pokfulam 0.0% 0.0% 0.0% 1.8% 11.2% 9.8% 7.5% 5.4%
Deep Water Bay & Repulse Bay 0.0% 0.0% 0.9% 7.4% 22.3% 30.4% 13.4% 7.2%
Wanchai Tin Hau 0.0% 0.0% 0.0% 2.9% 7.5% 14.9% 13.9% 5.8%
Wan Chai North 0.0% 0.0% 0.0% 1.8% 1.8% 16.7% 3.7% 4.8%
Happy Valley 0.0% 1.8% 0.0% 2.8% 9.0% 21.6% 9.1% 4.5%
Islands (Map)
District Location Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Islands Cheung Chau 0.0% 0.0% 6.6% 10.4% 14.1% 9.2% 9.7% 6.5%
Tung Chung 0.0% 0.0% 0.0% 5.1% 11.0% 9.0% 3.1% 0.0$
Kowloon (Map)
District Location Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Yau Tsim Tsim Sha Tsui 0.0% 0.0% 2.5% 3.4% 13.0% 17.7% 13.3% 5.6%
Tsim Sha Tsui East 0.0% 0.0% 1.9% 4.6% 6.5% 22.5% 19.2% 14.7%
Mong Kok Mong Kok 0.0% 0.0% 0.0% 0.0% 3.2% 6.7% 6.7% 5.1%
Sham Shui Po Cheung Sha Wan 0.0% 0.0% 1.7% 4.3% 3.5% 8.7% 5.2% 5.3%
Lai Chi Kok 0.0% 0.0% 0.0% 0.9% 0.9% 4.8% 2.8% 0.0%
Sham Shui Po East 0.0% 0.0% 1.0% 5.5% 6.7% 12.4% 6.5% 3.7%
Kowloon City Ho Man Tin 0.0% 0.0% 0.0% 4.7% 10.0% 25.9% 16.7% 12.3%
Kowloon City North 0.0% 0.0% 0.9% 5.5% 9.1% 22.9% 15.5% 5.6%
Hung Hom 0.0% 0.0% 0.0% 1.8% 3.6% 9.8% 17.3% 8.8%
Lok Fu West 0.0% 0.0% 0.8% 4.4% 12.1% 13.6% 8.4% 6.0%
Kai Tak North 0.0% 0.0% 2.7% 7.8% 6.6% 12.8% 9.2% 5.1%
Wong Tai Sin Wong Tai Sin Central 0.0% 0.0% 1.5% 12.0% 39.6% 30.4% 14.7% 10.4%
Diamond Hill 0.0% 0.0% 0.0% 3.5% 5.2% 13.3% 6.0% 3.6%
Ngau Chi Wan 0.0% 0.0% 2.9% 8.2% 9.5% 25.0% 17.1% 9.4%
Kwun Tong Kwun Tong Central 0.0% 0.0% 4.8% 8.7% 9.6% 10.4% 11.9% 12.0%
Lam Tin 0.0% 0.0% 0.0% 4.2% 10.2% 10.2% 8.5% 8.7%
Yau Tong 1.3% 0.0% 1.4% 17.8% 24.3% 15.9% 15.7% 18.8%
Kowloon Bay 0.0% 0.0% 4.9% 10.2% 17.6% 27.2% 10.0% 5.7%
The New Territories (Map)
District Location Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Sai Kung Tseung Kwan O South(Formerly Tseung Kwan O) 0.0% 0.0% 0.0% 12.9% 10.5% 18.5% 13.4% 5.6%
Tseung Kwan O North 0.0% 0.0% 5.6% 20.6% 7.3% 21.2% 15.3% 12.0%
Sai Kung Town 0.0% 0.0% 3.7% 15.7% 11.1% 14.8% 10.2% 3.7%
Sha Tin Tai Wai 0.0% 0.0% 0.0% 6.3% 12.0% 20.2% 12.7% 11.3%
Sha Tin East (Formerly: Yuen Chau Kok) 0.0% 0.0% 0.0% 1.7% 4.2% 9.4% 7.6% 12.6%
Ma On Shan 0.0% 0.8% 0.0% 2.3% 9.4% 42.2% 23.4% 19.5%
Sha Tin Town Centre and Fo Tan (Formerly: Wo Che) 0.0% 1.0% 1.9% 7.4% 19.3% 30.3% 15.0% 10.1%
Tai Po Tai Po 0.0% 0.0% 0.9% 4.5% 18.0% 23.1% 10.7% 4.5%
North Fanling 0.0% 0.0% 0.0% 0.9% 15.2% 9.8% 2.6% 7.0%
Sheung Shui 0.0% 0.0% 0.0% 2.6% 29.3% 24.3% 24.6% 17.4%
Yuen Long Tin Shui Wai 0.0% 0.0% 0.0% 5.0% 22.0% 12.9% 7.9% 9.0%
Yuen Kong 0.0% 0.0% 6.0% 0.0% 6.1% 4.1% 8.0% 4.0%
Yuen Long Town 0.0% 0.0% 0.0% 1.8% 10.1% 11.5% 3.8% 4.5%
Tuen Mun Tuen Mun North 0.0% 0.0% 0.0% 2.3% 16.9% 12.4% 4.7% 2.3%
Tuen Mun South 0.0% 0.0% 0.0% 4.6% 3.7% 8.2% 4.6% 4.6%
Tuen Mun West 0.0% 0.0% 2.0% 8.2% 32.0% 11.6% 5.2% 5.3%
So Kwun Wat 0.0% 0.0% 0.0% 2.7% 11.9% 24.5% 7.3% 5.5%
Tsuen Wan Tsuen Wan Town 0.0% 0.0% 0.0% 1.7% 6.9% 4.2% 6.0% 1.7%
Tsuen Wan West 0.0% 0.0% 1.0% 4.9% 7.6% 16.3% 9.5% 4.7%
Ma Wan 0.0% 0.0% 2.0% 2.0% 12.0% 16.3% 16.3% 8.0%
Sheung Kwai Chung 0.0% 0.0% 2.8% 5.5% 6.5% 4.7% 4.6% 3.8%
Kwai Tsing Kwai Chung 0.0% 0.0% 2.8% 2.0% 8.7% 11.0% 3.8% 6.7%
Lai King 0.0% 0.0% 2.8% 14.7% 8.4% 24.5% 9.5% 5.9%
Tsing Yi South (Formerly Tsing Yi) 0.0% 0.0% 0.0% 3.4% 9.5% 9.5% 6.1% 0.0%
Tsing Yi North 0.0% 0.0% 0.0% 3.0% 7.5% 11.7% 9.7% 1.0%
Port areas (Map)
Port Area Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Hong Kong International Airport 0.0% 0.0% 0.0% 0.7% 0.8% 0.6% 0.5%
Cross Boundary
Check Points on Land
0.0% 0.0% 0.0% 1.0% 2.6% 6.1% 4.3%
Private Cargo Working Areas 0.0% 0.0% 0.3% 2.5% 5.7% 7.8% 6.6%
Cross Boundary Ferry Piers 0.0% 0.0% 0.0% 0.3% 2.2% 5.7% 4.2%
Container Terminals 0.0% 0.0% 0.0% 0.1% 0.6% 1.3% 1.0%
Public Cargo Working Areas 0.0% 0.0% 0.0% 1.1% 3.0% 4.4% 5.4%

Mosquito prevention

Advice

To the public

The public is advised:

To the management of construction sites

The management of construction sites is advised:

Mosquito control

Adult Control

Larval Control