Welcome to our insectary in Mali!

Posted 20th December 2018

There is a buzz within the Malaria Research and Training Center, which is set within the lush green grounds of the University of Sciences, Techniques and Technologies of Bamako, Mali.

Along one of the university’s many tree-lined paths is the recently renovated insectary, which today houses two mosquito colonies used by the team. One is a local wild Anopheles coluzzii strain established from mosquitoes captured in local villages, which was brought into the lab for individual oviposition (egg laying) and molecular identification, and is maintained in the insectary for future studies. The other is a strain of Anopheles gambiae sl mosquito that has a naturally occurring (i.e. non-genetically modified) heritable trait that causes a white pigment “collar” on the back of the mosquito larvae, which can be visualised under a microscope by a trained eye. The colour variant strain can be maintained by selecting specific colour variant female mosquitoes (that have the white “collar” pigmentation), and crossing them to male mosquitoes that do not.

Housed in the insectary are all four life cycle stages of both colonies, from the wet paper disks onto which females have laid freshly laid eggs, the rows of trays containing the aquatic larval stages, to the pots containing the pupae, and the cages containing adults that are ready to produce the next generation of mosquitoes.

Despite how easy the team make it look, a great deal of meticulous work goes into maintaining these two colonies. For starters, the freshly hatched larvae are kept in trays in low numbers to ensure they have enough space and access to nutrients to grow as healthily and as stress-free an environment as possible. The larvae are fed fish-food that has been carefully ground and supplied to the bottom of the trays with pipettes so that they can grow and develop through their four moulting stages in a clean environment in which they thrive. Once the mosquitoes enter their final immature stage as pupae, they are picked out of the trays and separated by their sex using the microscope to visualise the different sexual characteristics. This step requires a great deal of specialist effort and a keen eye. The pupae are then placed in cages and all emerged adult mosquitoes, both males and females, are provided with a source of sugar that mimics the nectar and plant juices that they feed on in the wild. In the wild, adult Anopheles females also take a blood meal from humans to source some important proteins for the development of their eggs. In the insectary, the team uses a membrane feeding technique that mimics the temperature and texture of human skin to attract the females, and to allow their piercing mouthparts to access the blood. Attention to detail is essential for the accuracy of all these steps.

To maintain the colonies, two types of mating occur: (1) between wild females and wild males to maintain the colony of wild mosquitoes, and (2) between colour variant female mosquitoes that have pigmentation with colour variant male mosquitoes with no pigmentation to maintain the colony of colour variant mosquitoes. This means that for the colour variant colony, there is an additional step to maintain the colony: larvae are investigated one-by-one under a microscope to identify and separate the mosquitoes that carry the white “collar” colour pigment. This larvae identification step is one of the many important ways in which our team in Mali are preparing for our future technology for malaria control (currently under development).

What’s also clear from the procedures in place for visitors is that the team do not take anything for granted, and are systematic and thorough when it comes to ensuring the safety and containment of mosquitoes. These considerations have influenced the design and operation of the lab so that it meets the national and international containment guidelines and regulations and best practices for handling mosquitoes in preparation for future works.

We are mindful of the challenges that malaria-endemic countries such as ours have to face to win the fight against a disease like malaria.