344 bytes removed ,  13:47, 20 August 2010
Line 22: Line 22:  
===Vectors===
 
===Vectors===
   −
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. 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.
 
+
.
3.2 Culicoides species have a normal insect complete metamorphosis life cycle –
  −
egg, four larval instars, pupa and adult. In temperate and cool regions they
  −
“overwinter” at the fourth larval instar stage. Some species enter diapause when the
  −
number of daylight hours declines below a threshold level but others are more
  −
influenced by temperature which affects their activity levels. The adult populations in
  −
Britain tend to fall dramatically from mid to late October. From December adults are
  −
usually either not at all detectable or only in very small numbers, depending upon the
  −
prevailing temperature, until April-May. These periods may be even longer in northern
  −
Britain. The life span of adults is usually about 10 days, but in cooler conditions their
  −
metabolism slows and they may survive for periods of more than a month.
      
Most species require a blood meal before laying eggs, although C. impunctatus (the
 
Most species require a blood meal before laying eggs, although C. impunctatus (the
6,502

edits