Research Paper on Mosquito

Research Paper on Mosquito:- 1. Habit and Habitat of Mosquito 2. External Structures of Mosquito 3. Inner Structures 4. Life History 5. Control.

Research Paper # Habit and Habitat of Mosquito:

Mosquitoes live in swarms and prefer to stay in tropical damp areas. These insects are said to be nocturnal but are also found to be active in daytime. It shows preference to dark colour.

The male mosquitoes are vege­tarian and live upon plant saps. It is the females which are sanguinivorous and suck blood from most land-living vertebrates in­cluding man. Any source of stagnant water serves as their breeding place and life cycle includes larval stages which are totally dis­similar from the adult. Thus the metamor­phosis is complete.

Research Paper # External Structures of Mosquito:

These small sized insects have the body divided into head, thorax and abdomen. A short neck connects the head with the thorax.

1. Head:

The head is small and more or less round. It contains following structures:

(i) A pair of prominent bean-shaped compound eyes,

(ii) In front of compound eyes a single triangular lobe, called clypeus, is present. It carries a pair of elongated antennae, one on each side of the head. The antennae are bushy in males,

(iii) The mouth is provided with appendages, called mouth parts or trophi (Fig. 18.87).

The mouth parts in males are for sucking but in females these are adapted for piercing and sucking. The differ­ent appendages form a structure, called pro­boscis.

The proboscis is well developed in females.

It consists of:

(a) One pair of nee­dle-like mandibles having sharp tips,

(b) One pair of needle-like first maxillae with sharp serrated tips. Each first maxilla carries a segmented maxillary palp on the outer side of the proboscis. The maxillary palps are longer in males than females,

(c) One pair of second maxillae are united to form labium. A groove is present on its upper side and its terminal end bears the white leaf-like lobes, called labellae, having numerous sensory hairs at the free end.

(d) The labrum and epipharynx are fused to form a single struc­ture with free sharp end. A groove is present on its lower surface,

(e) A chitinous blade­like hypopharynx with pointed tip, bears the opening of salivary, gland at its base.

The hypopharynx and epipharynx unite to form a tube through which blood is sucked. Labellae of the labium rest over the skin, the mandibles cut the skin, and first maxillae, epipharynx and hypopharynx enter within the skin. In males, mandibles are absent and hypopharynx is fused with the labium.

2. Thorax:

It consists of one large (meso-thorax) and two small segments (prothorax and metathorax). The thorax carries one pair of wings and three pairs of walking legs, one pair in each segment. The legs are built up in typical insect pattern, but tarsus is long and coxa is short in each leg.

The wings are borne on the mesothoracic segment (second thoracic segment) and are effectively used in flying. They are spotted in Anopheles. Second pair of wings are extremely small, ill-developed and modified as the halters and these are used as balancing and sensory structures. In Culex, the wings beat at the rate of 278-307 per second. The lateral side of the thorax carries stigmata.

3. Abdomen:

Abdomen is long and narrow. It is covered by scales which are arranged in an imbricate fashion. Only the females con­tain abdominal appendages in the form of pair of knob-like ovipositor. The eighth seg­ment carries anal opening. Reproductive opening is present on the ninth segment.

Research Paper # Inner Structures of Mosquito:

The alimentary canal (Fig. 18.88) consists of:

(a) Mouth:

This contains several append­ages and it leads to the pharynx;

(b) Pha­rynx:

It works as a pumping organ to suck the fluid;

(c) Oesophagus:

It is a narrow straight tube with three reservoirs or diver­ticula. Two anterior oesophageal diverticula and one large posterior oesophageal diverticulum are present at the anterior and at the poste­rior ends respectively. The oesophagus leads to the stomach and the opening is guarded by an oesophageal valve,

(d) Midgut or stomach:

It is a straight tube running up to hindgut. In between midgut and oesopha­gus thick-walled Proventriculus is present. Near the junction of mid- and hindgut, nu­merous thread-like Malpighian tubules open;

(e) Hindgut or intestine:

Hindgut or intestine funs straight up to the anus. Two sets of salivary glands, each with three lobes, are the digestive glands of mos­quito. These are placed below the alimentary canal and remain in the thoracic region.

The alimentary canal is adapted for tak­ing a heavy meal. The saliva, produced by salivary glands, contains enzymes which prevent coagulation of blood. The blood is sucked by the pumping of pharyngeal wall, and after mixing with saliva is stored in the oesophageal reservoirs. It then passes through the stomach and intestine.

The heart of Anopheles is muscular but non-neurogenic. In the heart of Culex poste­rior ostia are present and its blood contains four types of proteins. In comparison to its size the eyes are quite large. In Culex, each facet of the eye measures up to 16 µm. Another feature also observed in Culex is the relationship of rhabdomes and retinular cells.

Here the rhabdomes are attached with the cytoplasm of retinular cells only at the proxi­mal end. The sensory structures are well developed. The adult mosquitoes can dis­criminate distilled water and NaCl solution by tarsal chemoreceptors. The feeling of warmth is an important factor in finding out the host.

Research Paper # Life History of Mosquito:

Fertilization is internal. Mating takes place during flight. The sound produced by a female mosquito attracts the flying males. After mating the female mosquito selects some stagnant water of low depth for laying eggs. The eggs float in water.

Anopheles eggs remain scattered and are provided with lat­eral air-floats (Fig. 18.89), the Culex eggs are arranged to form a raft (Fig. 18.90) by the movement of the hind legs of the female.

These eggs remain attached with the raft by means of the surface tension of water. At the posterior end of each egg a water droplet condenses which is gradually absorbed in course of development. The larva which comes out of the egg is aquatic and its body is divisible into three parts—head, thorax and abdomen.

The head possesses a pair of lateral compound eyes and an opening, called mouth. The mouth parts are represented by a pair of maxillae, a pair of mandibles and a bunch of hair-like feeding brushes. The larva eats algae and micro-organisms. The thorax is the broadest part and contains tuft of hairs.

The abdomen consists of nine seg­ments and has bundles of lateral hairs and a long and pointed siphon. The siphon con­tains air-tubes each of which has two spiracles and terminal flaps at the outer end. The secretion of a gland, called peri-piracular gland, around the spiracle, helps the larva to float on the surface of the water. The air- tubes are in connection with the inner branched network.

The anal segment bears tracheal gills which carry on aquatic respira­tion. The anal papillae in larva constantly absorb water which is again eliminated as urine. The larval integument plays an impor­tant role in aquatic respiration. The larva of Anopheles floats parallel to the surface of the water, but the Culex larva remains under water and only the terminal end of the siphon peeps through the surface of the water.

The ascent of larva depends upon the lack of oxygen and not on excess carbon dioxide. In course of development, the larva transforms into pupa. The pupa is mobile but it does not eat anything. The anterior part is broad and called the cephalothorax.

The narrow abdomen contains nine seg­ments. A pair of large fins on the eighth segment work as organs of swimming. The dorsal side of the thorax bears a pair of small respiratory trumpets, the openings of which are guarded by numerous hairs.

Within the pupa rapid transformation takes place; only a few cells produce the adult structure by using up most of the pupal material. The full-grown mosquito comes out by breaking the pupal skin along the dorsal side. Immediately after coming out of the pupal case, the mosquito rests on the floating shell for a while to dry up and then takes off into the air.

The biological organisation of different mosquitoes is basically similar. The differ­ences between Anopheles and Culex, two very common genera of mosquitoes, are shown in Table 18.6—Arthropoda.

Research Paper # Control of Mosquito:

By transmitting various diseases, the mosquitoes not only endanger human lives but also incapacitate millions of working hands. Therefore, all necessary measures should be taken against them.

Following preventive measures are usually adopted:

1. Mosquito needs stagnant water (even a little collection of water on the sur­face of leaf is enough) for breeding. Thus measures should be taken to clear all such sites where water-logging takes place.

2. Spray of kerosene, detergents and in­secticides in the breeding areas serve the purpose.

3. Effective biological control can be done by introducing larvae-eating fishes.

4. Mosquito-nets and curtains should be used to prevent the bite of mosquito.