Artificial visual environments to enhance mating success in colonised Anopheles funestus

BACKGROUND: Establishing and maintaining laboratory colonies of the malaria vector, Anopheles funestus using newly collected material has proven challenging, in part because of their low propensity to mate in captivity. In this study we assessed how cage conditions influence the mating success of two An. funestus strains originating from different geographic areas, Angola (FANG) and Mozambique (FUMOZ). METHODS: The visual environment in adult mosquito-rearing cages was manipulated either by covering the cages in different planes with black opaque cloth (referred to as black horizons) or by placing black visual markers at various positions inside the cages. Mating success was assessed by dissecting the spermathecae capsule of the females after the standard 10-day mating period. RESULTS: Insemination rates were consistently higher in the An. funestus FANG strain than in the FUMOZ strain in both the black horizon (odds ratio [OR] 0.31, 95% confidence interval [CI] 0.21-0.44, p < 0.001) and visual marker experiments (OR 0.12, 95% CI 0.08-0.19, p < 0.001). The inclusion of black horizons and visual markers significantly increased insemination in both strains (p < 0.001). However, strain-specific responses were evident: FANG showed significantly greater insemination rates in the side-covered cages (OR 2.06, 95% CI 1.41-3.01, p < 0.001), whereas FUMOZ insemination rates declined under the same condition (OR 0.41, 95% CI 0.24-0.70, p < 0.001). The insemination rate of the FUMOZ strain was significantly higher in top-covered cages (OR 0.59, 95% CI 0.38-0.95, p = 0.03) and when a visual marker was placed at the bottom of cage (OR 2.18, 95% CI 1.25-3.81, p = 0.006), while FANG insemination rates were unaffected by marker position. CONCLUSIONS: This study demonstrates that manipulating the visual environment within adult mosquito-rearing cages can significantly enhance mating success in An. funestus, although the effectiveness of specific visual cues varies between strains. While both FANG and FUMOZ responded positively to visual enhancements, their differing responses to the same conditions underscore the importance of tailoring rearing protocols as mating stimuli at their original location may be associated with specific environmental features. These findings offer preliminary guidance for improving the colonisation and maintenance of An. funestus in laboratory settings, while highlighting the need for further research to improve mating success for this species.