Seasonal abundance, host seeking and resting behaviours of Anopheles gambiae and An. funestus complexes in Mazowe and Shamva districts, Zimbabwe.

BACKGROUND

OBJECTIVES

Determining the host seeking and resting behaviours of malaria vectors in a locality is vital for the design and implementation of locally adapted vector control strategies. This study investigated the seasonal abundance, host seeking, and resting behaviours of malaria vectors in localities where insecticide-treated nets (ITNs) and indoor residual spraying (IRS) are persistently used in Mazowe and Shamva districts, Zimbabwe.

METHODS

Anopheles mosquitoes were sampled from both living and non-living structures using CDC light traps, Prokopack aspirator, and artificial pit traps in April, July, October, and December 2023. Female Anopheles were identified using morphological keys. R software was used for data analysis. The Kruskal-Wallis test was used to assess differences in the abundance of female Anopheles across collection methods, while a negative binomial Generalized Linear Mixed Model (GLMM) was used to determine the effect of study site, season, and type of structure on the abundance of female Anopheles mosquitoes.

RESULTS

Overall, 787 female Anopheles were caught, comprising An. gambiae sensu lato (s.l.) (33%), An. funestus s.l. (17.4%) and others (49.6%). Relative abundance of female Anopheles mosquitoes based on collection method showed significant difference (Kruskal-Wallis: X 2 = 42.33, df=3, p<0.001). There were significantly more female Anopheles mosquitoes caught in Shamva district (p=0.023), during the post-rainfall season (p<0.001), in traditional-style bedrooms (p<0.001) and grass thatch toilets (p=0.045). Notable proportions of An. gambiae s.l. were caught seeking hosts pre-bedtime outdoors (19%) and early morning outdoors (14.3%), and An. funestus s.l. pre-bedtime indoors (14.5%) and early morning outdoors (10.9%). High percentages of An. gambiae s.l. (51.1%) and An. funestus s.l. (35.6%) were caught from non-living structures that lack insecticide treatment.

INTERPRETATION

CONCLUSION

Malaria vectors are circumventing current control measures by biting people when they are not protected by ITNs and resting in outdoor areas or indoor structures where insecticides are not applied. Supplementary interventions, including larval source management (LSM) and repellents, are required to reduce the risks of residual malaria transmission.