Access to mosquitoes with known pedigrees is vital to many research projects in the MRP and also to malaria control programmes. Establishing and maintaining such colonies of mosquitoes is the primary objective of the insectary.
Mr Ashok Saikoolal, a qualified animal laboratory technologist, manages the facility, assisted by Mr Joseph Shozi and Mr Mzwakhe Roald Cibane.
Acquiring the colonies:
Some of our colonies have been donated by other entomologists and are
already adapted to colony life. It is more difficult to catch
sufficient numbers of local wild mosquitoes, confirm that they are all
the same species ( see species
identification ) and then facilitate their adaptation, step
by step, to living and breeding in the insectary. We attempt to recreate
some of the essential conditions of the mosquito's natural environment:
high temperature and high humidity are maintained by air conditioners;
lights are provided with dimmers on a timer control to create an artificial
dusk and dawn (essential for successful mating). Adaptations to new food sources
are very important: adults must adapt to feeding on anaesthetised guinea
pigs, and the larvae to finely ground commercial cat pellets.
Maintaining the colonies:
A very high standard of cleanliness, careful regulation of larval
feeding (frequency and quantity), regulation of numbers of larvae per
tray, and careful egg collection are all important. Great care also
has to be taken to prevent cross-contamination of the species, many
of which will interbreed in these conditions.
Invading ants must also be kept at bay. They can decimate a mosquito colony virtually overnight.
Species kept:
With the spread of drug resistance and its impact
on chemoprophylaxis of malaria, the WHO have placed new emphasis on personal
protection against mosquito bites.
Field tests are notoriously difficult to conduct and are subject to the vagaries of the weather, insect populations etc. While laboratory tests cannot replace field tests, they represent an effective way for preliminary testing of candidate repellents or different formulations of repellents, as they can be conducted under carefully controlled conditions with known populations of insects all at the same state of physiological development. In addition the human volunteers are not exposed to the risk of possible infection by arboviruses.
Controlled application of repellent to forearms
Bioassays: At regular intervals after the application
of repellent, treated forearms are exposed to thirty unfed female
mosquitoes for a two minute period. The mosquitoes are contained in a cage
with a gauze top and a transparent bottom. The cage is applied
to the arm gauze side down and mosquitoes bite through the gauze and
can be observed and counted through the transparent bottom. Using
the data thus generated statisticians can calculate protection times.
Malaria control programmes direct efforts at two
different levels: vector control and patient detection. Vector control in
South Africa depends on spraying insecticide onto internal surfaces of houses
in the malarious areas. Until 1995 DDT was used, but this has
now been replaced by synthetic pyrethroids, which are effective against
mosquitoes but more environmentally friendly. 
But which one to use? There are many different synthetic pyrethroids on the market, and we know that different house construction materials interact with the insecticides in different ways.
Laboratory evaluation: This is a rapid way to test a number of different insecticides and formulations at different application rates on typical surfaces (various mud daubs, wood, cement and paint) without the expense and risk to human population of a field trial. Once suitable candidates have been identified field trials follow.
Target preparation: Mud, cement plaster formed into discs.
Insecticide application: precise doses of insecticide sprayed onto targets with Potter's Spray Tower.
Bioassay: Insectary supplies large numbers of female malaria mosquitoes ( Anopheles arabiensis ) which are exposed to the treated surfaces by placing them in conical cages attached to the targets, and recording number of deaths occurring within a 24hr period after one hour of exposure. These assays are repeated at regular intervals for up to 1 year and give a reliable indication of the insecticide's effective life.
Molecular techniques have become very important in identifying
species and genetically characterising populations. For example
some of the vectors of malaria in Africa belong to a species complex, the
members of which cannot be identified on morphological characteristics.
Predominant among the molecular techniques is the Polymerase Chain Reaction (PCR).
This technique (which earned its inventors the Nobel Prize) is highly sensitive and specific and operates by repeatedly duplicating short sections of DNA characteristic of a particular species, producing enough of the amplified product to be visible after gel electrophoresis.
