Mosquito Background
Mosquitoes are two-winged flying insects that are found in many parts of the world. Mosquitoes belong to the order Diptera and the family Culicidae, which is split into three subfamilies: Anophelinae, Culicinae and Toxorhynchitinae. There are 41 genera and approximately 3500 species of mosquitoes. Diptera is the order of True Flies, meaning they have two wings, but unlike most flies mosquitoes have scales on their wings.
Mosquitoes have a complex lifecycle that has four distinct stages. These are egg, larva, pupa and adult. Egg: Mosquitoes lay their eggs individually directly onto the water surface. Eggs are generally laid on still water such has ponds, lakes, or stagnant water. Females can lay 50-200 eggs per oviposit (CDC 2012). The eggs themselves have unique floats on either side to help remain on the surface of the water. Generally, the eggs are will hatch within 24 hours. Larvae: The second stage of the mosquito lifecycle is the larvae stage. Mosquito larvae are aquatic and have a segmented abdomen, a large thorax and a head with mouth brushes as seen in Figure 3. The larvae lie parallel to the surface of the water and use their mouth brush to filter feed on organic matter. Unlike other genera of mosquito, Anopheles don’t have a breathing siphon and instead acquire oxygen through the palmate hairs that line their abdomen. They are usually found on the surface of the water but dive below when disturbed by a jerky movement of the whole body. Larvae develop through four stages called instars, which involves shedding its exoskeleton to accommodate its growth. Pupae: The pupae stage of mosquitoes is shaped like a comma and spends much of its time at the surface of the water where it can breathe through a pair of respiratory trumpets. The pupae has two main parts, the cephalothorax (head and thorax) and the tail (abdomen). The wings, legs and mouthparts develop inside the cephalothorax during this stage which means that it can’t feed as a pupae. This stage lasts a few day. Adult: The cephalothorax of the pupae splits and the adult mosquito emerges. The adult mosquito has a thin body with a head, thorax and abdomen section as seen in Figure 5. The head has the eyes and two segmented antennae which are used for detecting odors. The head also contains two sensory palps and a long proboscis used to feed. 3 pairs of segmented legs and one pair of wings are attached to the thorax of the adult mosquito. The abdomen is utilized to digest food and develop eggs. Both males and females feed on nectar and other plant sugars but females also require a blood meal, during which the abdomen can expand. Adults are most active during the night and spend days resting in dark areas. The female mosquito only feeds on blood in order to develop eggs. Blood contains hemoglobin which is rich in protein essential for nourishing the eggs. It is this behavior which causes the transfer of malaria. If the female bites an infected individual, it can then spread the disease to others she bites. The feeding is possible because of the specialized feeding apparatus that is the proboscis. The proboscis consists of a bundle of feeding stylets referred to collectively as the fascicle and a large outer lip called a labium. Only the fascicle actually penetrates the sin during feeding, the labium buckles back to rest on the skin’s surface (Wong & Wu 2010). The fascicle contains saliva glands that secrete anti-coagulants into the feeding site to stop the blood from clotting (Stark & James 1996). |