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The arthropd vector for bluetongue virus is the ''Culicoides'' biting midge. 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. In warm conditions, adults survive around 10 days, but this can be extended to up to a month when the weather is cooler. The activity of ''Culicoides'' varies with the time of day: the midges 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. ''Culicoides'' generally avoid entering buildings and other closed spaces.
 
The arthropd vector for bluetongue virus is the ''Culicoides'' biting midge. 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. In warm conditions, adults survive around 10 days, but this can be extended to up to a month when the weather is cooler. The activity of ''Culicoides'' varies with the time of day: the midges 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. ''Culicoides'' generally avoid entering buildings and other closed spaces.
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Most species require a blood meal before laying eggs, although C. impunctatus (the
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Scottish highland biting midge), a member of the C. pulicaris group, does not require a
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blood meal for maturation of the first egg batch. This enables this midge to persist in
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areas with few mammalian hosts.
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3.3 Different Culicoides species have different preferences for breeding sites
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ranging from damp dung, damp soil to tree holes, streamsides and the edges of ponds.
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The C. obsoletus group breeds in damp soil and composted organic material such as
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old manure heaps common around stables and animal housing. The C. pulicaris group
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prefers to breed in wet soil, sphagnum marsh and bogs.
   
3.4 Culicoides imicola is the major vector of BTV in the Old World. It is one of the
 
3.4 Culicoides imicola is the major vector of BTV in the Old World. It is one of the
 
most widely distributed of Culicoides species. It occurs throughout most of Africa, the
 
most widely distributed of Culicoides species. It occurs throughout most of Africa, the
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common throughout central and northern Europe. Both of these species are widespread
 
common throughout central and northern Europe. Both of these species are widespread
 
throughout most of the British Isles.
 
throughout most of the British Isles.
3.6 In practice, the usual reference to C. obsoletus really relates to a complex of
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closely related species (C. obsoletus, C. dewulfi, C. scoticus, C. chiopterus, C.
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montanus) the females of which are difficult or impossible to separate. In Bulgaria, C.
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obsoletus and C. scoticus, at least, co-exist. Since it is the females that are the vectors
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of BTV, it is not always possible to determine the identity of the vector when
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undertaking virus isolation from midges. In the UK, C. obsoletus, C. dewulfi, C.
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scoticus and C. chiopterus occur. These C. obsoletus group species belong to a larger
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grouping (subgenus Avaritia) that includes C. imicola (the major European and
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African BTV vector) and C. brevitarsis (the major Australian BTV vector). A similar
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taxonomic situation exists with C. pulicaris which is a complex of morphologically
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similar species, eight of which occur in the UK and with C. nubeculosus, a European
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species which is closely related to the North American BTV vector C. sonorensis (= C.
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variipennis).
   
3.7 The distributions of C. obsoletus and C. pulicaris group midges in UK are not
 
3.7 The distributions of C. obsoletus and C. pulicaris group midges in UK are not
 
well understood. Observations of both have been made in many parts of the British
 
well understood. Observations of both have been made in many parts of the British
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