SECTION 6 - MIDGES
Biting midges are found world-wide and are in the genus Culicoides along with mosquitoes. Many prey on other insects whilst others feed on mammals or birds - only a few feed on humans. There is one dominant species that causes nuisance by biting humans Culicoides impunctutaus. Other species found include Culicodes obsoletus (the garden midge), Culicoides halophilus (associated with salt marshes) and Culicoides nubeculosus (commonly found in stables and cattle sheds).
The egg and pupal stages are very short (a few days) but the larval stage lasts for around 10 months.
Some larva live in muddy margins of lochs, some on salt marshes and others in farmyards or drainage ditches. The Highland Midge prefers blanket bog, raised mires or poorly drained acidic grasslands. The larvae need significant moisture and hence are concentrated in high rainfall areas. Midges can drift passively for more than 1km from larval breeding grounds and this is one reason why localized larval treatment is of limited use as the midges can travel a large distance. In sheltered woodland sites there is much less dispersion and hence a greater concentration of biting.
Midges are biting and blood-sucking insects and one of the main impacts arises from the irritation caused by the bite. There are many diseases for which midges are vectors but few transmissible to humans and even fewer indigenous to the UK.
Midges have a habit of attacking in numbers generally in the evenings. Whilst they are active between April and October, most biting occurs from June to August.
Habitat manipulation - given the concentration of midges (estimated at up to 24 million larva per hectare) and the distance of travel, wholesale landscape modification is not feasible. However on a localized basis it has been found that dam construction to flood land and keep standing water between the midge and the breeding ground can help control midges.
Insecticide and Larvicide applications - the larval breeding grounds of the Highland Midge are associated with damp areas of rough moorland bearing Sphagnum or Polytrichum mosses and the rush Juncus articulatus. The larvae occur within the top 10mm of soil and treatment relies on washing the larvicide into the soil (thus rain is key to successful treatment).
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