Maintaining Aedes aegypti Mosquitoes Infected with Wolbachia

Aedes aegypti mosquitoes infected with Wolbachia are being released into natural populations to suppress the transmission of arboviruses. We describe methods to rear Ae. aegypti with Wolbachia infections in the laboratory for experiments and field release, taking precautions to minimize laboratory adaptation and selection.

Transcript

The overall goal of this protocol is to describe the maintenance of the Aedes aegypti mosquitoes infected with Wolbachia. These mosquitoes are being released around the world to suppress the transmission of dengue and other viruses. Our protocol for rearing Aedes aegypti mosquitoes can be used by any researchers who are interested in using mosquitoes for experiments or disease control programs.

This method can also be used for rearing genetically modified mosquitoes for mosquito population control programs, including those that involve sterile insect release. The principles involved in this approach can also be applied to the rearing of other disease vector species. For this protocol, house the mosquitoes at approximately 26 degrees Celsius and at 50 to 70%relative humidity with an equatorial photo period.

If they are reared at higher temperatures, the Wolbachia infections could be lost, so do not overheat the colonies. Maintain around 500 mosquitoes per population to minimize inbreeding. Using this protocol with adequate nutrition will yield 28 day generations.

Begin with eggs on a substrate. Submerge them in trays containing three liters of water with about 300 milligrams of fish food and a few grains of active, dry yeast to induce hatching. One day after hatching, use a glass pipet to transfer approximately 500 larvae to trays containing four liters of water and fresh fish food.

Check the trays daily to ensure that the larvae have sufficient food. Add about 600 milligrams of fish food every other day to maintain an optimal food supply. Overfeeding can result in water clouding and thus mortality, so replace the water as needed.

If nutrition and temperatures are maintained correctly, the larvae will pupate five to seven days after hatching. And adults will emerge approximately two days later. Seven days after hatching, pour the entire contents of the tray through a fine mesh.

Retain some of the filtered water in a five liter container for ova position in the same colony. Next, invert the mesh, and dip it into a plastic container with 200 milliliters of water to transfer the pupae. Add the appropriate amount of food to feed any remaining larvae.

Now, set up an adult emergence cage with two cups of 10%sucrose solution and two cups of moist cotton balls to prevent desiccation. If the pupae do not need to be sorted by sex, transfer the container of pupae into a cage, and leave the lid slightly ajar for the adults to escape and enter the cage. After all of the adults have emerged, remove the container from the cage.

Do not select against slow developers by taking the container out sooner. To collect virgin mosquitoes, transfer the pupae from the larval rearing trays to plastic containers with 200 milliliters of water every 24 hours. Sort the sexes by size.

Females are larger than males. And transfer them to separate containers. Keep the lids closed on the containers so the adults do not escape.

Before releasing the emerging adults into their cages, confirm their sex. Incorrectly sexed adults must be removed using an aspirator within 24 hours of emergence while they are still sexually immature. To keep the Wolbachia infected colonies similar to a natural population, cross the infected females from the lab to uninfected wild males.

Mature the males and females separately for two days. And then aspirate the females into the male cage. Ideally, set up a one to one sex ratio with a population size of around 500.

Proceed to outcross the mosquitoes for at least three consecutive generations. At least three days after the last adults emerge, and before they are two weeks old, blood feed the colony before excessive female mortality occurs. This is particularly important for mosquitoes with Wolbachia infections that shorten lifespan.

The sugar cups should be removed the day before. Give the mosquitoes access to a forearm, and wear a latex glove to protect the hand and wrist. Most females should be fed within five minutes.

But it can take up to 15 minutes. Once all the females are visibly engorged, remove the forearm, and replace the sugar cups. Two days after blood feeding, place two plastic cups filled with water and lined with a partially submerged strip of sandpaper into the cage.

Then, remove any other water source except for the sugar water. The females will oviposit on the sandpaper just above the water line from three days after blood feeding. Collect and replace the sandpaper daily until no more eggs are laid.

If more eggs are needed, blood feeding can be performed at weekly intervals. Partially dry the sandpaper with about 30 seconds of gentle blotting using a paper towel. Do not dislodge the eggs.

Then, wrap the strips in a sheet of dry paper towel, and place it into a sealable plastic bag. Three days post collection, inspect the eggs under a dissecting microscope. If the sandpaper is too wet, the eggs may hatch before being submerged in water.

But if it dried too harshly, the eggs may collapse. The eggs are ready to hatch three days after collection. Submerge all the eggs from each colony into the same container of water to produce a large pool of individuals for the next generation.

Generally, eggs can be stored in a sealed container with a humidity greater than 80%at 20 degrees Celsius for several months. But some Wolbachia infections reduce viability, so these eggs should be hatched within a week of collection. When larvae containers were provided with 0.25 milligrams of food per larva per day or less, the development time increased for both sexes and was less synchronous than in containers provided with more food.

If adequate food is not provided throughout the duration of development, this will negatively impact colony maintenance. Slowly developing individuals might be selected against, and blood feeding may be delayed. There may even be increased adult mortality before reproduction.

Sub-optimal nutrition affected adult morphology. Wing lengths decreased substantially and correlated to nutrition levels. Uniform body sizes are important to experimental comparisons as body size is positively associated with fecundity, and large mosquitoes should be more fit under field conditions.

After watching this video, you should have a good understanding of how to maintain Aedes aegypti mosquitoes infected with Wolbachia. Following our protocol should ensure that healthy mosquitoes of a consistent quality are produced. These mosquitoes can then be released into the field for disease control programs or be used for experiments.

When working with Wolbachia infected mosquitoes, it is important to monitor their infection status to ensure that the colonies maintain their Wolbachia infections.

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Journal (Biology)

Journal (Biology)

Maintaining Aedes aegypti Mosquitoes Infected with Wolbachia

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