Mosquitoes and Their Life Cycle

Introduction

Mosquitoes are, ironically, the most popular insect vectors of animal diseases across the world. Female mosquitoes are hematophagous, feeding on vertebrate blood for egg production and maturation. Different species of mosquitoes prefer different hosts. During feeding, a female mosquito injects her proboscis and discharges saliva inside the host’s skin, causing an itchy reaction. If this mosquito is carrying disease pathogens from an earlier blood meal, after sufficient pathogen development (incubation) in its body, the pathogen may be transmitted to the new host. The incubation period varies for every pathogen ranging from days to weeks.

Mosquitoes are vectors of human diseases like

• Dengue fever

• Yellow fever

• Arboviral encephalitis

• Zika

• Chikungunya

• Malaria, and

• Filariasis

Mosquitoes cannot survive in moving water bodies. They prefer to live in stagnant pools and seepage water near flowing water streams. The life-cycle, pattern-egg laying, and larval habit depend on the selection of habitat. Based on their habitat preference, mosquitoes can be categorized in standing waters (permanent or transient) and flood water (natural or artificial containers). Species living in standing water lay their eggs singly or in rafts on the surface of the water and can survive for several broods in harsh environmental conditions after mating and blood engorging. But species living in floodwaters, deposit their eggs in a separate location due to periodic flooding of the area, near damp soil, inside tree holes and artificial containers. They produce one to many broods annually and can overwinter their eggs in harsh environments. Mosquitoes are adapted to changing climates and environments, therefore can adjust to multiple habitat types for their growth and survival.

Life Cycle and Developmental Stages

A major part of the life of a mosquito is spread in water, only the adult stage causes harm to human and animal health. The knowledge of every life cycle stage is important to initiate measures of control before maturing into adults. Every mosquito goes through four distinct stages-egg, larva, pupa, and adult to complete its life cycle, but the length of each stage depends on the ambient temperature and food sources.

• Egg − Mosquito species can be divided into two categories depending on the location of eggs laid-floodwater mosquito species lay their eggs above the water surface level because of periodic flooding they can survive for three months to two years and standing water mosquito species lay eggs on the surface of standing water bodies like permanent pools, eggs are laid singly or in clutches, each consisting of hundred to two-hundred eggs forming egg rafts. These eggs hatch within twenty-four to forty-eight hours depending on environmental conditions.

• Larva − On hatching from eggs, mosquito larvae are formed which molt through four instars, increasing in size with each molt. Larvae breathe vigorously atmospheric oxygen and lay horizontally or at a forty-five-degree angle to the water surface. Some larvae puncture the underwater plant cells to receive oxygen and never come to the surface.

• Pupa − The fourth instar larva is transformed into a comma-shaped structure after molting called the pupa. This is the transition phase between aquatic stages to the terrestrial stage of a mosquito’s life cycle. Pupas do not feed and undergo tumbling motion to escape predation. Pupa molts and within twenty-four to forty-eight hours, the pupa will molt into an adult.

• Adult − After emergence adult mosquitoes seek a protective environment and hide in the surrounding vegetation to complete the development of their wings. Males emerge before females and mate with the female as soon as she is capable. Both require carbohydrate sources for nourishment which are derived from the nectar of flowers and plant juices to maintain energy for flying, mating, and finding hosts for blood meals. Only female mosquitoes require bloodmeal to get extra protein for egg development. Intake of bloodmeal is the way mosquitoes acquire viruses, protozoans, and helminths and transmit them to humans and other animals. Male mosquitoes can live only for one or two weeks, while females may survive up to producing multiple batches of eggs. Some species of mosquito can overwinter after consuming bloodmeal and live for several months

The life cycle of three important mosquitoes - Aedes, Anopheles, and Culex are studied, they show different morphological differences in their developmental stages which are a useful source of information in vector control and elimination programmes.

Comparison between Aedes, Anopheles, and Culex mosquitoes

Conclusion

The life cycle of mosquitoes is divided into four stages-egg, larva, pupa, and adult. Larva and pupa develop in an aquatic environment. On fertilisation and maturation, female mosquitoes deposit their eggs in moist surfaces of soil, mud or fallen leaves. Rain fills these areas, and stimulates the hatching of the eggs. Egg hatching and larval development are a constant ongoing process. About one week is taken by the egg to hatch and mature into an adult. After emergence, adult mosquito mates, and females feed on blood for nutrition and egg development. Only females are known to bite animals for a blood meal. Adult males feed on plant juices and usually die shortly after mating. The average lifespan of a mosquito is about two to three weeks.

FAQs

Qns 1. What is the length of a mosquito's life cycle?

Ans. It is about two to three weeks.

Qns 2. Which stage of the life cycle is most harmful?

Ans. The pupal and adult stage is the most dangerous stages.

Qns 3. Where do mosquitoes lay eggs?

Ans. Mosquitoes usually lay eggs in stagnant water.

Bitopi Kaashyap

Updated on: 15-Dec-2023

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