Biting and Resting Behaviours of Malaria Vectors in Rural Burkina Faso Following Scaling up of LLINs

Background: Long Lasting Insecticide-Treated Nets (LLINs) and Indoor Residual Spraying are the most common and successful methods for malaria vector control in Africa. However, studies in areas of sub-Saharan Africa with high LLIN coverage suggest vectors are adapting their biting and resting behaviours minimising their contact with these tools. In combination with growing insecticide resistance, such vectors behavioural shifts could significantly reduce the efficacy of LLINs. Changes in major malaria vector behaviours have not been yet documented in Burkina Faso. Here we investigated spatial and temporal variation in malaria vector abundance, biting and resting behaviour in Burkina Faso in the 2 years following a mass LLIN distribution. Methods: A longitudinal mosquito vector surveillance was initiated (September 2016 November 2018) within 12 villages in south-western Burkina Faso. Host-seeking and resting malaria vectors were collected in and outside of houses on two days per month from 19h to 06h using respectively Human Landing Catch and Resting bucket. Results: A total of 47,654 mosquitoes males and females were collected, with most being from the Anopheles gambiae s.l. species complex. (96.74%). Within this complex, An. coluzzii (53.82%) and An. gambiae (45.9%) were the dominant species. Controlling for seasonality and spatial variation, there was an overall decline in malaria vector abundance across the study period (z=-2.49, p=0.02). Contrary to expectation, the An. gambiae s.l. community was relatively exophagic (~54% biting outdoors) with no evidence of longterm trend. Malaria vector biting time peaked between 00h-02h but showed some variation between villages (df =11, F =2.46, p=0.009) and earlier biting in dry season, (F=3.81, p<0.0001). Exophily was also common in An. gambiae (~60% resting outdoors) while An. coluzzii was more endophilic (~35% resting outdoors). Conclusion: This study revealed a long-term decline in abundance but no evidence of longterm shift in biting location and time over the study period. While this degree of outdoor biting in this area was higher than anticipated, the late-night timing of outdoor bites indicates that majority could still be prevented through use of LLINs. However, further investigation and analysis of the behaviour and population dynamics of these vector populations is still needed to improve control strategies