Which biting fly is known to be a biological vector of African horse sickness?

Culicoides, also known as biting midges or "no-see-ums," are recognized as the biological vector of African horse sickness. This disease is caused by a virus that primarily affects equines, and Culicoides play a critical role in its transmission.

These small insects are particularly adept at biting and feeding on the blood of animals, including horses, and during this feeding process, they can introduce the virus into the host's bloodstream. The lifecycle of Culicoides allows them to carry and transmit the African horse sickness virus effectively, making them a significant concern in regions where the disease is prevalent.

In contrast, Stomoxys calcitrans, also known as the stable fly, is primarily a nuisance fly and is not associated with the transmission of this particular virus. Simulium, commonly referred to as black flies, are known for their biting behavior but are not vectors for African horse sickness either. Hippobosca includes species such as the horse fly, which also does not serve as a biological vector for this disease. Thus, Culicoides is uniquely positioned as the key insect in the transmission of African horse sickness, clarifying why it is the correct answer.