Mosquitoes and deeer flies transmit diseases that cause a great deal of harm to human beings

Both malaria and yellow fever are spread by specific mosquitoes in Central and South America and Africa.

Loa loa filariasis is carried by deer flies in Africa.

Where there are no human beings, these diseases can cycle in the animals of the rainforest.

Mosquitoes

Mosquitoes need water in which to lay their eggs, and the rain forest provides an abundance of suitable sites. Each type of breeding location has its particular mosquito species.

In Africa, some inhabit water-filled tree holes; others prefer leaf axils and a range of species breed in pools on the forest floor.

The larvae of most mosquitoes are filter feeders, but those of Toxorhynchites brevipalpis are carnivorous and feed on other mosquito larvae that use understory tree holes.

Adult mosquitoes are highly mobile within the rainforest and often take part in daily vertical migrations.

Several species, including Aedes ingrami, move down toward the relative coolness of the rainforest floor during the day and return to the canopy layer at dusk.

Although Aedes africanus breeds in low-level tree holes, it generally feeds on monkeys that live in the canopy.

Only female mosquitoes are on blood. Their mates subsist mainly on flower nectar.

Female mosquitoes of the tropical rainforest have a range of feeding patterns. Some feed throughout the day, with specific peaks of activity; others are inactive except for short feeding periods, often at sunset.

Mosquitoes also feed at specific levels in the rainforest.

To take a blood meal, the mosquito pierces the victim's skin, and then pumps saliva into the wound to prevent the blood coagulating as it sucks.

This injection of saliva causes the irritation of a mosquito bite. It is also a major factor in the spread of disease. The infective agents are transmitted in the mosquito's saliva.

Yellow Fever

Yellow fever is a viral disease endemic in equatorial Africa and Central and South America. It is mostly transmitted by the mosquito Aedes aegypti.

It originates in Africa, producing only minor symptoms in indigenous monkeys and humans.

In South America, however, the disease frequently kills its monkey and human hosts.

Yellow fever has an incubation period of five days and for two of these, virus particles are present in the bloodstream.

During this short time, mosquitoes taking a blood meal pick up the virus.

In humans, yellow fever causes vomiting, fever, jaundice and often death.

Deer Flies

Deer flies show many behavioral similarities to mosquitoes. The adults lay their eggs in damp regions, and the larvae feed on moist plant debris. Adult deer flies favor open habitats and will feed on humans at river margins or in rainforest clearings produced by tree felling.

Loa loa filariasis

Loa loa filariasis, caused by the parasitic worm Loa loa, is transmitted by deer flies. The adult worm, about two inches long, lives in the connective tissue between the skin and muscles of monkeys and human beings.

The worms move about the body searching for mates, irritation and swelling, particularly at the joints. Although disabling, the disease is not usually fatal.

When male and female worms meet, they mate and produce larval worms, or microfilariae, which live in the bloodstream. During the day in humans and at night in monkeys, the microfilariae congregate in the blood vessels of the skin and so are in the best position to be taken up by a feeding deer fly.

The microfilariae grow in the fly and change into a new larval form that is infective humans. The next takes time the fly takes a blood meal these infective larvae enter the new human host and develop into adults that may live for more than a decade.