Yeah, this lecture will be on black flies, which are the major vectors of Onchocerciasis. Black flies fall under the family Siumuliidae and they're the major vectors of Onchocerciasis. In the African region Simulium damnosum complex and Simulium neavei complex are the major vectors involved in the transmission of Onchocerciasis. In Latin America, there are two major species which are Simulium metalicum and Simulium ochraceum. Simulium damnosum complex then is a major vector of Onchocerciasis as we have said and it's a complex consisting of over 40 species, or forms, and these adapted to different ecological conditions. The most important ones in West Africa include Simulium damnosum sans strictum and Simulium sirbanum. These are common in savannah areas, and they are involved in transmission of severe form of the disease, which leads to blindness. We also have in this study a Simulium yahense and a Simulium soubrense. These are forest zone species and they are responsible for the less severe form of the disease involving skin manifestations. Now, let's look at the morphology of black flies. It's a small dark fly with a humped thorax, as you can see, as you can see here. They've got short tenna, short, short antenna, which is similar both sexes. The mouth parts are of sucking type, which have been modified and, for sucking, but they're capable of slashing the skin. It's actually that the blood is the continued food, blood. The life cycle of Simulium damnosum starts with eggs which are laid massively on vegetation touching on fast flowing water or any obstruction which happens to be within the flowing river or streams. The eggs hatch into larvae with six to seven instars. These have got hooks for attachment and mouth brushes for feeding. As you can see some of those here, and also it's more clear on this, on this picture. Simulium damnosum then hatches into larvae and there are six to seven instars. These are hooks for attachment as you have seen in the picture and mouth brushes for feeding. They have the ability to move up and down the flowing water. The pupae then attaches itself to substrate, which has got filaments for feeding. The complete cycle takes two to three weeks depend, depending on the climatic conditions, and the adult has ability to survive for three weeks. Simulium neavei, this one is very much attached to crabs, and they live on people that live in fresh water. They feed on fine particles, which include small water organisms using their mouth brushes. It is common in wood habitats and most of the forest habitats in West, in East Africa. Let's look at the biology of Simulium damnosum. Adults will occur in large swarms in areas with swift flowing streams which provided the required air that's needed for development. The adults bite outdoors during daytime. It's, it's it has got in two habits unlike mosquito, which feeds during the nighttime, with peaks in the morning and afternoon. The nulliparous, that is those ones which have not laid eggs, normally feed in the morning. And the parous ones, these are the adults which have laid eggs one or two times or more than that, these are the ones which are fondest to feed in the afternoon. Simulium damnosum has a tendency to bite close to the ground, and mostly below the knee. Simulium, Simulium damnosum are capable of long flights, even up to 300 kilometers with, of course, with assistance of wind, but usually they remain close to the breeding sites. The Latin American species, that is the Simulium Ochraceum and metallicum, are normally found in forest mountain habitats with small streams in Central America. They have got short flight range, about ten kilometers. And unlike the Simulium damnosum which feed on the lower part of the body, these ones feed on the upper human body where the microfilarial densities are high. And the highly anthropophilic entities that are strongly attracted to feeding on human. Simulium metallicum is also found in the Americas, but mainly in the southern part of America in the highland and lowland areas. This one, unlike the species which I just mentioned, is, has got high zoophilic tendencies. That is, capable of feeding on human as well as on animals. Simulium guianense, which is another species in Latin America is normally found in the Amazon highlands, and it has high natural infection, but low vectorial capacity. Now let's look at Larviciding. Larviciding is the most successful method, method for control. Since sulfide works, is not located at resting sites for the adult. The type of Larvicide, which is normally used depends on the effectiveness, environmental friendliness, and also the mammalian toxicity. Insecticides which will fit this criteria are quite few. Initially DDT was successfully used in control of Simulium neavei in East Africa, specifically in Kenyan highlands. But it cannot be used now because of the environmental concerns. Temephos and Bacillus thuringiensis are the ones which are being used effectively, especially in West Africa and Guatemala where there are large control programs. The application then has to be intermittent. It has to be targeted at the breeding sites which are normally areas with the sort of structures or waterfalls. And this can be done by either hand application or by aerial larviciding.
