Tsetse flies

body, in this case, of the tsetse fly.
  CUTICLE
Like all other insects, the tsetse fly has a tough outer covering or cuticle. The whole of the body is covered with cuticle, even the eyes. Mast parts are hard, but some areas remain flexible, especially the base of the wing, the joints on things and where the mouth parts join on to the head; these parts can therefore be moved easily. The cuticle on the underside (ventral side) of the abdomen in the tsetse fly is elastic, so that it can stretch when the abdomen takes up the large blood meal
Movements of the legs are controlled by muscles attached to the inside of the cuticle of the legs; rapid movement of the wings for flying is controlled by very large muscles in the thorax.

or grey-brown; sometimes there is a slight pink or sandy-red tinge. Several species are very dark. The body usually has darker and lighter patches, making the insect difficult to see when it is settled on bark, rock or soil. At rest, the tsetse normally appears quite slim because the wings are placed one over the other on the back (Figure 1.3), not projecting outwards at an angle to the body as in house flies or most blowflies. Immediately after a blood meal the tsetse abdomen is large, rounded and red.
The body is made up of three main parts: the head, the thorax (to which are attached the wings and legs) and the abdomen. These parts will now be described in greater detail

Each of these eyes is composed of thousands of small units, called ommatidia (singular: ommatidium). The part of the ommatidium that forms the surface of the eye is the lens. The lenses near the midline of the head are slightly larger than those at the sides of the head. The compound eyes of some species are said to be able to detect moving objects at 137 metres (150 yd). They are very good for nearer vision and a small movement near the insect can make it fly off. The compound eyes are dark brown in the living fly.
Simple eyes At the top of the head are three simple eyes or ocelli (singular: ocellus); these are also sensitive to light, but their exact function is un certain.
 Antennae  There are two antennae placed at the front of the head in a depression between the two compound eyes. Each antenna has three segments of which the third is the largest, and bears the arista.

has a row of branched hairs on its upper side.
The third antennal segment also has on it two small holes leading to the olfactory pits, which contain many sensilla (sensory hairs) that can small the air. The antenna is therefore an organ serving the sense of smell.
 Ptilinal suture  This is a thin line that partly surrounds the part of the face carrying the antennae. It marks the place where the ptilinum (a balloon-like structure) comes out when the fly begins to emerge from the pupa . After emergence the ptilinum is folded back inside the 'head, and only the ptilinal suture can be seen from the outside.

They are long and narrow and can pierce the skin of an animal, so that blood can be sucked up into the fly; at the same time saliva can be passed down the mouthparts into the animal being fed on.
When the fly is not feeding, all the mouthparts are held so that they point forwards from beneath the head.
A pair of maxillary palps help to protect the more delicate proboscis or haustellum which lies between them when it is not in use.
The proboscis is very narrow (Figure 1.6) • It is made up of three parts, the labium, the labrum and the hypopharynx 

the free end it has a large number of very small teeth (labellar teeth). The teeth can cut their way through the skin of an animal, so that the fly may suck blood. The other end of the labium, where it is attached to the head of the fly, is swollen. This part (the thecal bulb) contains the muscles that cause the teeth to move.
 Labrum The labrum forms a tube through which blood is sucked up from the animal being bitten. The tube is called the food canal.
 Hypopharynx The hypopharynx is an extremely narrow tube through which saliva is pumped into the host animal as the fly feeds

The three pairs of legs are attached to the underside of the thorax, and the two wings are attached to the top of the side walls of the thorax.

wings. It has seven visible segments, or parts, and in the male there is, in addition, an extra structure (hypopygium) folded beneath the last two segments . On the dorsal (upper) side of the abdomen there are strong plates (each plate is called a tergite), one for each segment; but the ventral side is made of highly elastic cuticle, which can stretch to allow the abdomen to carry the enormous blood meal, and in the case of the female, the large larva. Remains of the blood meal can often be seen within the abdomen if examined from the ventral surface.
There are seven pairs of spiracles (breathing holes) along the sides of the abdomen. The anus is at the posterior end of the abdomen.
 The male genitalia  The word genitalia means parts used for mating. When the male tsetse fly is looked at from the ventral side, a rounded structure can be seen at the posterior end of the abdomen. This is the hypopygium. Just in front of the hypopygium is a plate bearing dark hairs called hectors

main part of each gland lies in the anterior part of the abdomen and it sends forward to the head a very narrow tube that joins with the one from the other side, before entering the hypopharynx .
When the fly feeds, saliva is sent forward from the glands and so down the length of the hypopharynx. It mixes with the blood meal as this is sucked up from the host's body. Saliva contains an anticoagulant, a substance that helps to prevent the blood meal from clotting in the mouthparts and anterior part of the alimentary canal.

labium. The teeth help to cut into the skin of the host. As the proboscis moves through the skin, the teeth cut the walls of small blood vessels (capillaries) and release the blood from them, forming a pool of blood under the skin (pool feeding).
 Pharynx 
The released blood is drawn up the food canal by the action of the muscles of the pharynx. When the fly is feeding, strong muscles in the head contract to make the space inside the pharynx larger, and this pulls blood up into the pharynx. When the muscles relax, the pharynx returns to its usual size, and the blood meal is sent on to the next part of the alimentary canal, the oesophagus.

coordinated by the nervous system. The fly is able to see, small and feel with the aid of its sense organs.
These send messages along nerves to the larger masses of nervous tissue in the head ('brain') and thorax (ganglion), which coordinate the sensory messages coming in, and send out other messages along other nerves to the muscles of the body, so that the fly moves (behaves) in an appropriate manner.
ENDOCRINE SYSTEM
Another messag sending system is the endocrine system. There are small glands in different parts of the body which release chemical substances (hormones)into the haemolymph, causing an appropriate reaction elsewhere in the body.
Processes such as pupation are under the control of the endocrine system.

larvae inside the body; these later emerge from the body fully grown. In order that the female fly may develop these eggs into larvae, the male fly has to make sperm and transfer it to the female (see 3.1).
 Male reproduction system The main parts of the male reproduction system are:
a pair of testes
a pair of accessory glands
a sperm pump
various ducts joining these other parts together.
The main function of the male reproduction system is to produce sperm and transfer these to the female, in order to fertilise the eggs.
Testes A testis is a coiled tube in which sperm is made and stored. The main part of the testis has a covering of orange or brown material, which makes it easy to see in dissections.

or instars, as it grows. There are three larval instars in Glossina up to the time when the fully grown larva is dropped by the female fly: the first, second and third instars. The larva has a mouth at the anterior end, and two posterior spiracles. The unusual feature of the Glossina life history is that the larva spends practically all its time, and does all its feeding, within the body of the female fly

It breaks out of the chorion  using a sharp egg tooth.
The first instar grows to 1.8 mm (G.morsitans)before changing to the next stage by getting rid of its old skin. The first instar lasts for about 1 day.
Second instar larva This is a stage of rapid growth and development. To either side of the posterior spiracles are swellings, and between the spiracles is an area of small spines.
The second instar lasts two days, and the larva grows to a length of 4.5 mm (G. morsitans).
 Third instar larva- This is also a stage of rapid growth and development. The fully grown larva has a pair of large black swellings at the posterior end. These are the polypneustic lobes, which carry many small holes through which the larva breathes. The polypneustic lobes are at first white, becoming black later. The rest of the larva is white in colour. Most of the weight and volume of the third instar larva is due to the gut which contains large amounts of unassimilated food. The third instar lasts just over two days and the larva grows to a length of 6–7 mm (G. morsitans).

produces a single egg which develops into a larva within her uterus. About nine days later, the mother produces a larva which burrows into the ground where it pupates. The mother continues to produce a single larva at roughly nine day intervals for her entire life.
The adult fly emerges from the pupa in the ground after about 30 days. Over a period of 12-14 days it matures, mates and, if it is a female, deposits its first larva. Thus 50 days elapse between the emergence of one female fly and the subsequent emergence of the first of its progeny.
This life cycle, with a slow reproductive rate and substantial parental investment in the care of young, is a relatively unusual example of an insect with a so-called 'K-type' life history.
This slow rate of reproduction means that tsetse populations can be eradicated by killing just 2-3% of the female population per day.
For a more detailed description of the life cycle and general biology of tsetse flies, see Stephen Leak's excellent book