Mosquito rearing is the process of breeding mosquitoes in a controlled laboratory environment. This practice produces large numbers of insects with known characteristics, such as age and species, which is fundamental for research. Maintaining colonies under specific conditions allows scientists to consistently study their biology and behavior. This controlled cultivation supports scientific investigations and public health strategies aimed at mitigating the impacts of these insects.
The Mosquito Life Cycle
All mosquitoes progress through four distinct stages: egg, larva, pupa, and adult. The first three stages are aquatic, while the adult stage is terrestrial and capable of flight. Female mosquitoes lay their eggs on or near stagnant water, with a single female capable of laying 50 to 300 eggs at a time. Depending on the species and environmental conditions, these eggs hatch within a couple of days when exposed to water.
Once hatched, the mosquito enters the larval stage, often called a “wriggler” because of its swimming motion. Larvae live at the water’s surface, breathing through a siphon and feeding on organic matter. This stage involves four growth phases, known as instars, and lasts between four and 14 days, influenced by water temperature and food availability. Following the final molt, the larva transforms into a pupa.
The pupal stage, or “tumbler,” is a non-feeding, mobile phase that lasts from one and a half to four days. Pupae are comma-shaped and remain at the water’s surface, breathing through two tubes called trumpets. Though they do not eat, they are sensitive to disturbances and will tumble into deeper water to escape threats. The adult mosquito emerges from the pupal case on the water’s surface, where it rests briefly before flying away. The entire cycle from egg to adult can be as short as five days in warm conditions but may take up to a month.
Essential Rearing Equipment and Environment
For the aquatic stages, laboratories use shallow, water-filled trays, often white, to make observing the larvae easier. These trays are made of plastic or stainless steel and are designed to be stacked on racks to maximize space within a climate-controlled room. Standardized trays, sometimes developed by organizations like the FAO/IAEA, allow for consistent larval densities. This consistency is a factor in producing healthy, uniform adults.
When larvae develop into pupae, they must be separated from the larval population. This is done manually by using a pipette to transfer the pupae into smaller cups or bowls. These containers are then placed inside adult containment cages. Adult cages are mesh-covered cubes with a cloth sleeve that allows technicians to access the inside to provide food or remove mosquitoes without allowing any to escape.
Rearing rooms are kept at a constant temperature around 27°C (80°F) and high relative humidity between 70% and 80%. These conditions are monitored daily with instruments to ensure consistency. A controlled photoperiod, a light-dark cycle set to 12 hours of light and 12 hours of dark, is also maintained. This cycle simulates natural day and night, which regulates mosquito activity like mating and feeding.
Nutritional Needs for Each Life Stage
For larvae, a consistent and nutrient-rich diet is supplied directly to the water in their rearing trays. Common larval foods include a finely ground mixture of brewer’s yeast, lactalbumin, and fish food or a slurry made from tuna meal and bovine liver powder. The amount of food is carefully measured. Overfeeding can foul the water, leading to bacterial growth and increased larval mortality.
Once mosquitoes emerge as adults, their dietary needs change. Both males and females require a constant source of sugar for energy, provided as a 5-10% sucrose solution. This sugar meal is supplied via a cotton ball or paper wick soaked in the solution and placed in a small cup inside the cage. This ensures the adults have a continuous food source for flight and survival.
While sugar provides energy for all adults, female mosquitoes of most species require a blood meal to develop their eggs. In a laboratory setting, this is provided using artificial membrane feeding systems. These systems, such as the Hemotek feeder, consist of a reservoir of blood covered by a membrane heated to 37°C (98.6°F) to mimic a live host. Defibrinated bovine or porcine blood is commonly used to ensure the colony’s continuation through egg production.
Applications in Research and Public Health
One major application of reared mosquitoes is the Sterile Insect Technique (SIT). This method involves rearing large numbers of male mosquitoes, sterilizing them with radiation, and releasing them into the wild. These sterile males then mate with wild females, whose eggs will not hatch. This process leads to a reduction in the target mosquito population over time.
Another use of reared mosquitoes is the deployment of Wolbachia, a naturally occurring bacterium. When female mosquitoes carry Wolbachia, it can block the transmission of viruses like dengue, chikungunya, and Zika. In one approach, both male and female mosquitoes infected with a specific Wolbachia strain are released, establishing the bacterium in the wild population. A different strategy, the Incompatible Insect Technique (IIT), releases only Wolbachia-infected males, which sterilize the eggs of wild females and cause a population crash.
Reared mosquito colonies are also used for testing new public health tools. Standardized cohorts of mosquitoes allow researchers to reliably assess the efficacy of new insecticides and repellents. Having a consistent supply of mosquitoes with a known species, age, and susceptibility profile ensures that test results are comparable and accurate. This is a necessary step in developing and validating new vector control products.