There are over 4,000 species of biting midges in the Ceratopogonidae family, and over 1,000 in just one genus, Culicoides. The distribution of midges in the genus Culicoides is world-wide; 47 species are known to occur in Florida. Species belonging to the genus Leptoconops occur in the tropics, sub-tropics, the Caribbean, and some coastal areas of southeast Florida.
Breeding areas can be very varied depending on the particular species. Areas with substantial salt marsh habitat are major producers of many biting midge species.
Additional sources for some species, like the bluetongue virus vector Culicoides sonorensis Wirth and Jones, include highly organic soil that is wet but not underwater such as those found with high manure loads in swine, sheep and cattle farming operations
Now, scientists at the Antwerp Institute of Tropical Medicine (ITG) have developed a molecular technique to easily and dependably identify the biting midges that spread bluetongue disease.
The same types of biting midges are also able to spread deadly African horse sickness, a disease seen as posing a growing potential threat to the European horse industry.
Until now, identification of biting midges was a problem.The technology developed by the scientists also helps to understand how bluetongue spreads, and how to control it. They report in the journal Medical and Veterinary Entomology.
Bluetongue primarily affects sheep, but cattle and other ruminants are also affected. It is not dangerous to people, but it causes great economical damage. Until a few years ago, the disease did not hit northern Europe.People assumed only tropical midges could transfer the responsible virus.
Also, the virus only replicated in the midges over 15 degrees Celsius. But in 2006 The Netherlands and Belgium were hit. Once the virus was present, local midges were shown to be capable of transmitting it.
Midges must be placed under a microscope and measured in minuscule detail, even down to the size of their genitals, to identify them. It was work for specialists.
The Antwerp researchers noted that if scientists did not know which midges transmit the disease, they would not know where it will spread, or where to fight the insects.
The researchers developed a simple and cheap molecular identification technology that identifies cullicoides species in the lab with 100 per cent certainty.
They concentrated on the most important species in northern Europe, Culicoides obsoletus, C. scoticus, C. chiopterus and C. dewulfi, but they can reliably identify more than 20 species.
Tests on larvae are also promising. Until now, there has been no way to differentiate larvae.
The scientists produced a "gene chip", or micro-array - a glass slide to which short pieces of DNA are attached - that are characteristic for each species. Such a slide can contain several dozens of different pieces of DNA, on well documented positions.
When the gene chip is washed with DNA from an unknown midge, identical pieces of DNA will recognize and stick to each other. This causes a blue colour reaction at that spot. The characteristic pattern of spots for each species can be recognized by the naked eye.
Contrary to other molecular identification tests, this one is very specific, and able to recognise several species at the same time. It helps to determinate midges that are difficult to recognise under the microscope.
When the French CIRAD (Centre for International cooperation and Research for Agronomy and Development) sent out a ring test to see which labs could identify four species of biting midges with molecular methods, ITG was the only institute to identify all samples correctly, three times in a row.