Name: maintaining aedes aegypti mosquitoes infected with wolbachia
Uploaded: 2017-08-14T15:00:00
Description: Watch this Scientific Journal Video about Maintaining Aedes aegypti Mosquitoes Infected with Wolbachia at JoVE.com

We acknowledge Heng Lin Yeap, Chris Paton, Petrina Johnson and Clare Doig for their contributions to the development of our colony maintenance methods, and three anonymous reviewers for their suggestions which helped to improve the manuscript. Our research is supported by a program grant and fellowship to AAH from the National Health and Medical Research Council and a translation grant from the Wellcome Trust. PAR is a recipient of an Australian Government Research Training Program Scholarship.

Blood feeding of mosquitoes on human subjects was approved by the University of Melbourne Human Ethics Committee (approval #: 0723847). All volunteers provided informed written consent.
1. Larval Rearing
NOTE: Mosquitoes are held at 26 &#177; 0.5 &#176;C and 50-70% relative humidity, with a 12:12 h (light:dark) photoperiod for this colony maintenance protocol. These conditions are similar to the average climatic conditions in Cairns, Australia and within the optimal t...

Following the protocol presented here for the maintenance of Wolbachia-infected Ae. aegypti should ensure that healthy mosquitoes of a consistent quality are produced for experiments and open field releases. In contrast to other protocols that prioritize the production of mass quantities of mosquitoes (see reference57), the methods are focused on maximizing their fitness, both within generations by implementing relaxed rearing conditions, and across generations by minimizing inbr...

Aedes aegypti mosquitoes are responsible for transmitting some of the most important arboviruses in the world, including dengue, Zika and chikungunya1. These viruses are becoming an increasing threat to global health as the widespread distribution of Ae. aegypti in the tropics continues to expand2,3,4. Female Ae. aegypti preferentially feed on human blood5 and thus tend to live in close proximity to humans, particularly in urban areas where populations are most dense. Through this close association with humans they have also adapted to breed in artificial habitats, including tires, pots, gutters and water tanks6,7. Ae. aegypti also readily adapt to laboratory environments where they can be maintained without any special requirements after being collected directly from the field, unlike some other species in the Aedes genus8,9,10. Their ease of maintenance has seen them studied widely in the laboratory in a broad range of fields, ultimately aiming to control the diseases mosquitoes may transmit.
Traditionally, arboviral control relies heavily on the use of insecticides to reduce mosquito populations. However, there is increasing interest in approaches where modified mosquitoes are reared in the laboratory and then released into natural populations. Released mosquitoes may be modified genetically11,12,13, biologically14,15, through irradiation16, chemical treatment17,18, or with combined techniques19 to either suppress populations of mosquitoes or replace them with mosquitoes that are refractory to arboviral transmission20.
Wolbachia are bacteria that are currently being used as a biological control agent for arboviruses. Several strains of Wolbachia were recently introduced into Ae. aegypti experimentally using embryonic microinjection21,22,23,24. These strains reduce the capacity of arboviruses to disseminate and replicate in the mosquito, diminishing their transmission potential23,25,26,27,28. Wolbachia infections are transmitted from mother to offspring, however certain strains induce sterility when infected males mate with uninfected females22. Wolbachia-infected males can therefore be released in large quantities to suppress natural mosquito populations, as recently demonstrated in other Aedes species15,29. However, since Wolbachia also inhibit arboviral transmission in Ae. aegypti, mosquitoes can also be released to replace native populations with poorer vectors. Ae. aegypti infected experimentally with Wolbachia are now being released into the field in several countries using this latter approach14,30,31.
Wolbachia-based approaches for arboviral control rely on a sound understanding of the interactions between Wolbachia, the mosquito and the environment. Wolbachia occur naturally in a broad range of insects, and the strains introduced into mosquitoes are diverse in their effects32. As new Wolbachia infection types are introduced into Ae. aegypti24, it is necessary to characterize each strain for their effects on mosquito fitness, reproduction and arboviral interference under a range of conditions. Rigorous experimentation in the laboratory is therefore required to evaluate the potential for Wolbachia strains to succeed in the field.
Open field releases of Ae. aegypti with Wolbachia infections can often require thousands to tens of thousands of mosquitoes per release zone to be reared each week14,30,31. The success of initial releases can be improved by releasing mosquitoes of a large size to maximize their fecundity33 and mating success34,35. Mosquitoes should also be adapted to the conditions they will experience in the field, however long-term laboratory rearing may cause changes in behavior and physiology which could impact field performance36,37,38.
We describe a simple protocol for rearing Ae. aegypti in the laboratory using basic equipment. This protocol is suitable for both wild-type and Wolbachia-infected mosquitoes, the latter of which can require special attention as some Wolbachia strains have substantial effects on mosquito life-history traits39,40. The rearing conditions avoid overcrowding and competition for food to produce mosquitoes of a consistent size, which is critical for vector competence and fitness experiments, and ensures that the mosquitoes are healthy for field release41. We also take precautions to minimize laboratory adaptation and inbreeding by reducing selective pressures and ensuring that the next generation is sampled from a large, random pool. However, laboratory environments are distinctly different from field conditions, and long-term maintenance under relaxed conditions could reduce the fitness of mosquitoes upon release into the field37,42,43. We therefore cross females from laboratory lines to field-collected males periodically, resulting in colonies that are genetically similar for experimental comparisons and that are adapted to the target field population39. The methods do not require any specialized equipment and can be scaled up to rear tens of thousands of individuals per week for field releases. The protocol also prioritizes the fitness of mosquitoes within and across generations, an important consideration for insects destined for establishment in natural populations. The protocol is suitable for most laboratories that require maintenance of Ae. aegypti, particularly for experimental comparisons where a consistent quality of mosquitoes and relatability to the field are important.

<table width="1661">
	<tbody>
		<tr height="24">
			<td height="24" style="width:287px;height:24px;">Wild type Aedes aegypti</td>
			<td style="width:168px;"></td>
			<td style="width:119px;"></td>
			<td style="width:1087px;">Collected from field locations in Queensland, Australia, see Yeap and others39 for details</td>
		</tr>
		<tr height="24">
			<td height="24" style="width:287px;height:24px;">w Mel-infected Aedes aegypti</td>
			<td style="width:168px;"></td>
			<td style="width:119px;"></td>
			<td>Provided by Monash University. Refer to Walker and others23 for information on the strain</td>
		</tr>
		<tr height="24">
			<td height="24" style="width:287px;height:24px;">w AlbB-infected Aedes aegypti</td>
			<td style="width:168px;"></td>
			<td style="width:119px;"></td>
			<td>Provided by Monash University. Refer to Xi and others21 for information on the strain</td>
		</tr>
		<tr height="24">
			<td height="24" style="width:287px;height:24px;">w MelPop-infected Aedes aegypti</td>
			<td style="width:168px;"></td>
			<td style="width:119px;"></td>
			<td>Provided by Monash University. Refer to McMeniman and others22 for information on the strain</td>
		</tr>
		<tr height="21">
			<td height="21" style="width:287px;height:21px;">Instant dried yeast</td>
			<td style="width:168px;">Lowan</td>
			<td style="width:119px;"></td>
			<td>Stimulates egg hatching. Found in general grocery stores. Other brands may be used</td>
		</tr>
		<tr height="21">
			<td height="21" style="width:287px;height:21px;">5 L plastic tub</td>
			<td style="width:168px;">Quadrant</td>
			<td style="width:119px;">Q110950</td>
			<td>Used for hatching and rearing larvae. Other products may be used</td>
		</tr>
		<tr height="21">
			<td height="21" style="width:287px;height:21px;">Fish Food (Tetramin Tropical Tablets)</td>
			<td style="width:168px;">Tetra</td>
			<td style="width:119px;">16152</td>
			<td>Provided to larvae as a source of food. Web address: https://www.amazon.com/Tetra-16152-TetraMin-Tropical-10-93-Ounce/dp/B00025Z6SE</td>
		</tr>
		<tr height="21">
			<td height="21" style="width:287px;height:21px;">Plastic containers</td>
			<td style="width:168px;"></td>
			<td style="width:119px;"></td>
			<td>Used for rearing larvae. Any plastic container above 500 mL should be suitable</td>
		</tr>
		<tr height="21">
			<td height="21" style="width:287px;height:21px;">Glass pipette</td>
			<td style="width:168px;"></td>
			<td style="width:119px;"></td>
			<td>Used for transferring larvae and pupae between containers. Web address: https://www.aliexpress.com/item/10Pcs-Durable-Long-Glass-Experiment-Medical-Pipette-Dropper-Transfer-Pipette-Lab-Supplies-With-Red-Rubber-Cap/32704471109.html?spm=2114.40010308.4.2.py4Kez</td>
		</tr>
		<tr height="21">
			<td height="21" style="width:287px;height:21px;">Clicker counter</td>
			<td style="width:168px;">RS Pro</td>
			<td style="width:119px;">710-5212</td>
			<td>Used to assist in the counting of larvae, pupae and eggs. Web address: http://au.rs-online.com/web/p/products/7105212/?grossPrice=Y</td>
		</tr>
		<tr height="21">
			<td height="21" style="width:287px;height:21px;">Rearing trays</td>
			<td style="width:168px;">Gratnells</td>
			<td style="width:119px;"></td>
			<td>Used for rearing larvae. Web address: http://www.gratnells.com</td>
		</tr>
		<tr height="21">
			<td height="21" style="width:287px;height:21px;">Nylon mesh</td>
			<td style="width:168px;"></td>
			<td style="width:119px;"></td>
			<td>Used to transfer larvae and pupae to containers of fresh water. Other brands may be used. Web address: https://www.spotlightstores.com/fabrics-yarn/specialty-apparel-fabrics/nettings-tulles/nylon-netting/p/BP80046941001-white</td>
		</tr>
		<tr height="21">
			<td height="21" style="width:287px;height:21px;">Cages</td>
			<td style="width:168px;">BugDorm</td>
			<td>DP1000</td>
			<td>Houses adult mosquitoes. Alternative products may be used. Web address: http://bugdorm.megaview.com.tw/bugdorm-1-insect-rearing-cage-30x30x30-cm-pack-of-one-p-29.html</td>
		</tr>
		<tr height="21">
			<td height="21" style="width:287px;height:21px;">35 mL plastic cup</td>
			<td style="width:168px;">Huhtamaki</td>
			<td style="width:119px;">AA272225</td>
			<td>Used to provide water or sucrose to adult mosquitoes. Other brands may be used</td>
		</tr>
		<tr height="21">
			<td height="21" style="width:287px;height:21px;">35 mL plastic cup lid</td>
			<td style="width:168px;">Huhtamaki</td>
			<td>GB030005</td>
			<td>Used to provide sucrose to adult mosquitoes. Other brands may be used</td>
		</tr>
		<tr height="21">
			<td height="21" style="width:287px;height:21px;">Cotton wool</td>
			<td style="width:168px;">Cutisoft</td>
			<td style="width:119px;">71841-13</td>
			<td>Moist cotton wool is provided as a source of water to adults. Other brands may be used</td>
		</tr>
		<tr height="21">
			<td height="21" style="width:287px;height:21px;">White Sugar</td>
			<td style="width:168px;"></td>
			<td style="width:119px;"></td>
			<td>Provided as a source of sugar to adult mosquitoes. Found in general grocery stores</td>
		</tr>
		<tr height="21">
			<td height="21" style="width:287px;height:21px;">Rope</td>
			<td style="width:168px;">M Recht Accessories</td>
			<td>C323C/W</td>
			<td>Used to provide sucrose solution to adults. Other brands may be used. Web address: https://mrecht.com.au/haberdashery/braids-cords-and-tapes/cords/plaited-cord/cotton/</td>
		</tr>
		<tr height="21">
			<td height="21" style="width:287px;height:21px;">Plastic cup (large)</td>
			<td style="width:168px;"></td>
			<td style="width:119px;"></td>
			<td>Used as an oviposition container. Any plastic cup that holds 100 mL of water should be suitable</td>
		</tr>
		<tr height="21">
			<td height="21" style="width:287px;height:21px;">Sandpaper</td>
			<td style="width:168px;">Norton Master Painters</td>
			<td>CE015962</td>
			<td>Provided as an oviposition substrate. Alternative products may be used, but we use this brand because it is relatively odorless. Lighter colors are used for contrast with eggs. Web address: https://www.bolt.com.au/115mm-36m-master-painters-bulk-roll-p80-medium-p-9396.html</td>
		</tr>
		<tr height="21">
			<td height="21" style="width:287px;height:21px;">Filter paper</td>
			<td style="width:168px;">Whatman</td>
			<td style="width:119px;">1001-150</td>
			<td>Used as an alternative oviposition substrate. Other brands may be used</td>
		</tr>
		<tr height="21">
			<td height="21" style="width:287px;height:21px;">Latex gloves</td>
			<td style="width:168px;">SemperGuard</td>
			<td>Z560979</td>
			<td>Prevents mosquito bites on hands when blood feeding. Other brands may be used. Web address: http://www.sempermed.com/en/products/detail/semperguardR_latex_puderfrei_innercoated/</td>
		</tr>
	</tbody>
</table>

maintaining aedes aegypti mosquitoes infected with wolbachia

Aedes aegypti mosquitoes experimentally infected with Wolbachia are being utilized in programs to control the spread of arboviruses such as dengue, chikungunya and Zika. Wolbachia-infected mosquitoes can be released into the field to either reduce population sizes through incompatible matings or to transform populations with mosquitoes that are refractory to virus transmission. For these strategies to succeed, the mosquitoes released into the field from the laboratory must be competitive with native mosquitoes. However, maintaining mosquitoes in the laboratory can result in inbreeding, genetic drift and laboratory adaptation which can reduce their fitness in the field and may confound the results of experiments. To test the suitability of different Wolbachia infections for deployment in the field, it is necessary to maintain mosquitoes in a controlled laboratory environment across multiple generations. We describe a simple protocol for maintaining Ae. aegypti mosquitoes in the laboratory, which is suitable for both Wolbachia-infected and wild-type mosquitoes. The methods minimize laboratory adaptation and implement outcrossing to increase the relevance of experiments to field mosquitoes. Additionally, colonies are maintained under optimal conditions to maximize their fitness for open field releases.

Figure 4 demonstrates the effects of suboptimal nutrition on the development of Ae. aegypti larvae. When containers are provided with 0.25 mg of food per larva per day or less, the development time increases for both males and females, and is less synchronous than in containers provided with 0.5 mg of food. If adequate food is not provided throughout the duration of larval development, this could have an adverse impact on the maintenance schedule. Sl...

Watch this Scientific Journal Video about Maintaining Aedes aegypti Mosquitoes Infected with Wolbachia at JoVE.com

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.

Maintaining Aedes aegypti Mosquitoes Infected with Wolbachia

Aedes aegypti mosquitoes experimentally infected with Wolbachia are being utilized in programs to control the spread of arboviruses such as dengue, ...

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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