Optimising adult housing and insectary lighting to increase mating success in colonised Anopheles funestu

Abstract

In nature, malaria vectors mate in swarms that form at dusk in relation to different ground markers that either affect the amount of light or contrast light at the point of swarm formation. Specific light regimes known to stimulate mating in mosquitoes have been simulated indoors for laboratory rearing of Anopheles. These conditions have proven effective for establishing and sustaining colonies of species in the Anopheles gambiae complex, but the same has not been achieved with members of the An. funestus group. Anopheles funestus sensus stricto, a main African malaria vector species in this group, has been difficult to colonise due to insufficient mating success in laboratory cages. This study aimed to optimise adult mosquito housing conditions to increase the mating success of two An. funestus strains housed under laboratory conditions. Mating success ratios were compared in different insectaries, cage sizes, and vector densities. The light environment in adult mosquito-holding cages was manipulated with artificial horizons and visual markers to simulate natural swarm cues. Mating success ratios did not differ between insectaries, but I found that cage size and manipulating adult mosquito-rearing cage by covering them with a cloth or placing a light-contrasting marker inside the cages increased mating success of An. funestus. Furthermore, the two geographically distinct An. funestus strains were affected differently by the same cage manipulation. Covering the top half of rearing cages with black opaque cloth and placing a black light-contrasting marker on the base of the cage significantly increased the mating success of An. funestus from Mozambique (FUMOZ strain). Contrastingly, the An. funestus from Angola (FANG strain) showed increased mating success in large cage sizes and when the side of the cage was covered in black cloth. The FANG strain had consistently higher mating success ratios compared to the FUMOZ strain. These findings indicate that the mating success ratios of An. funestus in the laboratory is likely to be influenced by geographical locations or underlying genetic diversities resulting in differences in the response of colony strain to the same mating-enhancement cues. Hence, adult mosquito housing should be customised when attempting to colonise and mass- produce An. funestus.