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The arthropod vector for bluetongue virus is the ''Culicoides'' biting midge. These are biological vectors of BTV, so the virus replicates in insect tissue after feeding on an infected host⁶.  It takes 10-14 days for the virus to dissminated from the insect's gut to its salivary glands, after which bluetongue virus may be transmitted to a new, susceptible ruminant host. This incubation period may be reduced when ambient temperatures are higher² and once infected, midges maintain BTV infection for life.

The arthropod vector for bluetongue virus is the ''Culicoides'' biting midge. These are biological vectors of BTV, so the virus replicates in insect tissue after feeding on an infected host⁶.  It takes 10-14 days for the virus to dissminated from the insect's gut to its salivary glands, after which bluetongue virus may be transmitted to a new, susceptible ruminant host. This incubation period may be reduced when ambient temperatures are higher² and once infected, midges maintain BTV infection for life.

These insects take blood meals from vertebrate hosts and breed in damp, dung-enriched soil enriched, and so are abdunant in the vicinity of domestic livestock. Once eggs are laid in soil, ''Culicoides'' progresses through four larval stages and pupates before becoming an adult midge. The lifecycle is greatly influenced by temperature: in temperate regions such as Britain, the adult midge population declines in October and is absent by December. The fourth larval stage overwinters, and adults re-appear the following April. The environment affects the activity of adult midges in a variety of ways. ''Culicoides'' survive around 10 days in warm weather but up to one month when conditions are cooler and are most active at night, from an hour before sunset to an hour after sunrise. Activity is decreased by windy conditions, and increased during the day when the weather is dull. Bluetongue virus replicates more rapidly in vector species when temperatures are warmer.  

''Culicoides'' take blood meals from vertebrate hosts and breed in damp, dung-enriched soil, and so are abdunant in the vicinity of domestic livestock. Once eggs are laid in the soil, ''Culicoides'' larvae progress through four stages and pupate before becoming an adult midge. The lifecycle is greatly influenced by temperature: in temperate regions such as Britain, the adult midge population declines in October and is absent by December. The fourth larval stage overwinters, and adults re-appear the following April. The environmental conditions also affect the activity of midges in several ways. ''Culicoides'' survive around 10 days in warm weather but up to one month when conditions are cooler and are most active at night, from an hour before sunset to an hour after sunrise. Activity is decreased by windy conditions, and increased during the day when the weather is dull. Bluetongue virus replicates more rapidly in vector species when temperatures are warmer.  

Classically, the major vector for BTV is ''Culicoides imicola''. This midge is found throughout Africa, the

Classically, the major vector for BTV is ''Culicoides imicola''. This midge is found throughout Africa, the

Middle East, southern Asia, Portugal, Greece, Corsica, Sardinia, Sicily and areas of Italy¹, and its distribution appears to be extending northwards. However, ''C. imicola'' has not yet been demonstrated in the United Kingdom. The ''Culicoides'' species found in the British Isles are ''C. pulicais'' and ''C. obsoletus'', which are also common across central and northern Europe. Knowledge of the distribution of these species in the UK is incomplete but the insects tend to gather where breeding sites and hosts occur in tandem, with the highest midge concentrations in areas containing cattle, horses and pigs. Removal of livestock decreases populations of ''Culicoides'' by a factor of 10 to 20¹, but some persist by feeding on wild animals and man. Hill sites have fewer midges as climatic conditions are less favourable, and sheep have a less positive influence on distribution.

Middle East, southern Asia, Portugal, Greece, Corsica, Sardinia, Sicily and areas of Italy¹, and its distribution appears to be extending northwards. However, ''C. imicola'' has not yet been demonstrated in the United Kingdom. The ''Culicoides'' species found in the British Isles are ''C. pulicaris'' and ''C. obsoletus'', which are also common across central and northern Europe. Knowledge of the distribution of these species in the UK is incomplete but the insects tend to gather where breeding sites and hosts occur in tandem, with the highest midge concentrations in areas containing cattle, horses and pigs. Removal of livestock decreases populations of ''Culicoides'' by a factor of 10 to 20¹, but some persist by feeding on wild animals and man. Hill sites have fewer midges as climatic conditions are less favourable, and the presence of sheep encourages the midge population less than that of cattle.

In Britain, studies are ongoing to determine midge distribution, seasonal incidence and the competency of the various ''Culicoides'' species to act as BTV vectors.

In Britain, studies are ongoing to determine midge distribution, seasonal incidence and the competency of the various ''Culicoides'' species to act as BTV vectors.