Background

  1. Complaints on insect bites caused by biting midges are received from time to time, particularly during summer months. This paper aims to provide some introductory remarks on this insect including its biology and control methods.

Insect Biology

  1. Biting midges are flies belonging to the family Ceratopogonidae. There are around 6000 species in 125 genera world wide and more than 1000 known species in China. Four genera, Austroconops, Lasiohelea, Leptoconops and most importantly Culicoides, feed on blood of vertebrates including human.
  2. Eggs are usually laid on surface of mud or wet soil, especially those with plenty of decaying plant materials, the major food source for the larvae. Biting midge larvae are aquatic or semi-aquatic, and can live in both fresh and salt water. Other breeding sites include tree holes, semi-rotting vegetation and the cut stumps of plants.
  3. Adults are about 1-4 mm long with dark body colour. They rest in dense vegetation and sometimes shady places. Their flight range varies but usually less than 100 meters from their breeding grounds. Despite having a short flight range, dispersal by wind is possible. While humidity plays a minimal role in the activity of biting midges, strong wind (over 5.6 km/hour) and low temperature (below 10°C) inhibit their flying. In fact, biting midges are such fragile insect that cool and dry weather will shorten their life span.
  4. Adults usually emerge in the summer and so it is the period when their nuisances are most serious. Only female adults bite for which extra nutrients are needed to stimulate the maturation of eggs. Biting activity varies among species but they are most active in day time or near sunrise and sunset. With short mouthparts, biting midges are unable to bite through clothing and so exposed body parts such as hands, arms, legs (when wearing shorts) and the head are most frequently attacked. Biting midges rarely bite indoors.

Local Situation

  1. In Hong Kong, at least 57 species from 10 genera of biting midges have been recorded. These species include Culicoides circumscriptus, C. circumbasalis, Dasyhelea ludingensis, D.horridus, D. abronica, D. bambusaoris, D.fornicatus, D. heyuxiani, D. apiculata, D. subechinatus, Forcipomyia appendicular, F. pennielongata, F. claudus, F bessa, F. bikanni, F. cavatus, F. surculus, F. fengjiensis, F. fuscimana, F. pulcherrima, F. brevilabellata, F. phototropisma, F. stelechos, F. wuxiensis, F. calleida, F. nanshengwei, F. yuani, F. frutetorum, F. lesliei, Lasiohelea mixta, L. taiwana, Bezzia datana, B. lujingi, Brachopogon halimos, Leptoconops hongkongensis and Stilobezzia chlorogastrula.

Public Health Importance

  1. To most people, the bites of biting midges cause acute discomfort and irritation. The irritation can last for days, or even weeks. Scratching aggravates the pruritus and may lead to bacterial infection and slow-healing wounds.
  2. Although a few Culicoides species are vectors of parasitic disease to human, the species found in Hong Kong is not documented carriers of filarial worms. In general, biting midges are not considered as very important human disease vectors.

Control Methods

  1. Adult midges can be controlled by space spraying of knockdown insecticide (e.g. fogging). Regular trimming of densely grown vegetation can reduce resting places for the adults. Personal protection measures should be employed, including installation of screens (mesh size <0.75 mm), wearing long-sleeved clothing and applying insect repellents such as diethyltoluamide, dimethylphthalate or trimethyl pentanediol.

  2. Breeding places for biting midges can be extensive and so complete disinfestations of larvae is difficult. Reduction of breeding could be achieved by:

    1. keeping the moisture content of soil surface low by techniques like plough or draining.
    2. removing refuse, fallen leaves and other decaying vegetation on slopes or on the flower beds as well as choking matters (e.g. muddy soil) in sand-traps/surface drainage channels.
    3. trimming, on a regular basis, densely grown vegetation to increase the exposure of soil surface to sunlight and air.
    4. applying residual insecticide at breeding places.

Pest Control Advisory Section