Biting Midges as Pests

Anyone with any significant outdoor experience knows that biting midges can be terribly annoying. They may occur in huge numbers in places where there is appropriate and abundant habitat and their bite (sometimes unnoticed at the time) can produce burning and itching welts completely out of proportion to their small size. As in virtually all other families of biting flies, only the females bite (they need the blood to develop their eggs). The culprits are restricted to two of the 33 genera known (or suspected to be) from Costa Rica: species of the genus of Leptoconops, with 4 species in Costa Rica and those of Culicoides, with 111 species.

Members of Leptoconops all breed in beach sand or alkaline soils. In Costa Rica the species are restricted to marine beaches and the adults tend to be daytime biters, generally on the lower legs (or the whole body if one is sitting or lying down). The females have a remarkable behaviour in which they bury themselves just under the sand surface when they are resting. One species in Costa Rica, L. becquaerti, transmits a filarial worm in humans called Dipetalonema ozzardi.

Adult Culicoides occur, in varying numbers, in virtually every region of Costa Rica, from the coast to the highest elevations. Despite the large number of species found in Costa Rica, only 12 have been recorded as feeding on humans. Of these only, Culicoides furens, C. phlebotomus, C. pseudodiabolicus, and C. paraensis occur in large enough numbers to be considered serious pests of humans. In particular, the well named C. furens, common near mangrove swamps, may occur in large numbers in Costa Rica and make life in some coastal areas a living hell!

Some other species feed on domestic animals. For example, Culicoides debilipalpis females feed on both humans and horses; C. arubae, C. foxi and C. barbosai have been collected from mules or horses and C. insignis have been collected from cattle. In large measure, we do not know what the other species of Culicoides feed on, although it is virtually certain that their hosts are other vertebrates.

There are two diseases which are transmitted by some species of Culicoides in Costa Rica. The first afflicts humans and involves two species of filarial worms: Dipetalonema ozzardi and D. perstans. The vector of these nematodes is likely C. furens but other species of Culicoides may also be involved.

Bluetongue is a viral disease infecting cattle and sheep which may result in their death. The disease is virtually worldwide and has different vectors in different regions of the globe. In Costa Rica the primary vectors are likely C. insignis, C. pusillus and possibly C. filarifer.

There are a number of other diseases of humans and domestic animals which occur elsewhere in Central America and in northern South America (e.g. Oropouche virus). Of these a number of the known vectors also occur in Costa Rica and there is, therefore, the possibility that these either occur undetected in Costa Rica or have the potential to spread there.

Considering the number of diseases of other vertebrates vectored by species of Culicoides in other, better studied regions, it is almost certain that some diseases of non-economic vertebrates in Costa Rica are transmitted by other species of Culicoides. Virtually no research, however, has been done on this.