Clustering of host-seeking activity of Anopheles gambiae mosquitoes at the top surface of a human-baited bed net

Abstract

BackgroundKnowledge of the interactions between mosquitoes and humans, and how vector control interventions affect them, is sparse. A study exploring host-seeking behaviour at a human-occupied bed net, a key event in such interactions, is reported here.MethodsHost-seeking female Anopheles gambiae activity was studied using a human-baited ‘sticky-net’ (a bed net without insecticide, coated with non-setting adhesive) to trap mosquitoes. The numbers and distribution of mosquitoes captured on each surface of the bed net were recorded and analysed using non-parametric statistical methods and random effects regression analysis. To confirm sticky-net reliability, the experiment was repeated using a pitched sticky-net (tilted sides converging at apex, i.e., neither horizontal nor vertical). The capture efficiency of horizontal and vertical sticky surfaces were compared, and the potential repellency of the adhesive was investigated.ResultsIn a semi-field experiment, more mosquitoes were caught on the top (74-87%) than on the sides of the net (p < 0.001). In laboratory experiments, more mosquitoes were caught on the top than on the sides in human-baited tests (p < 0.001), significantly different to unbaited controls (p < 0.001) where most mosquitoes were on the sides (p = 0.047). In both experiments, approximately 70% of mosquitoes captured on the top surface were clustered within a 90 × 90 cm (or lesser) area directly above the head and chest (p < 0.001). In pitched net tests, similar clustering occurred over the sleeper’s head and chest in baited tests only (p < 0.001). Capture rates at horizontal and vertical surfaces were not significantly different and the sticky-net was not repellent.ConclusionThis study demonstrated that An. gambiae activity occurs predominantly within a limited area of the top surface of bed nets. The results provide support for the two-in-one bed net design for managing pyrethroid-resistant vector populations. Further exploration of vector behaviour at the bed net interface could contribute to additional improvements in insecticide-treated bed net design or the development of novel vector control tools.

Behavioural responses of females of two anopheline mosquito species to human-occupied, insecticide-treated and untreated bed nets

“…Despite this, these results and those of others [23] show that an understanding of mosquito behaviour around the occupied bed net could inform bed net design in important ways. For example, higher levels of An.…”

“…This method tacitly assumes that mosquito pressure is the same on all parts of the bed net which this work and others’ [23] show not to be the case. Assuming that mosquito pressure at a given location on the bed net is proportional to mosquito entry rate when there are holes at that location, for the species studied here, a hole of a given size in the middle of the roof of the bed net would let in many more mosquitoes than the same size hole at the mid-level on the side of the bed net.…”

A minimal 3D model of mosquito flight behavior around the human baited bed net

“…The growing body of data arising from those 23 studies not only builds the evidence base required to accelerate the development process, 24 but it also provides an excellent foundation for developing models of host-seeking 25 behavior and experimentally validate the new tools at earlier stages. This paper 26 describes one such model: a fine-grained agent-based approach for modelling how indoor 27 insecticide treatments deployed as residues on bed nets affect the behavior and survival 28 of mosquitoes. 29 To capture the complex interactions between mosquitoes and a human host lying 30 beneath an insecticide-treated bed net, individual mosquito flight paths and local 31 interactions within the indoor environment are required.…”

“…Initial studies on mosquito behavior at bed nets used adhesive coated netting to map 67 the final position of mosquitoes at the bed net surface; by showing a preference for the 68 net roof, the attractant plume rising from the human host beneath was described 69 indirectly [28,29]. This approach is limited as the initial contact site might not be the 70 ultimate preferred destination while mosquitoes adhering to the net surface are 71 essentially removed from the 'pool' of mosquitoes available to study further activity.…”

“…To our knowledge, this is the first fine-grained model to simulate mosquito flight and 305 distribution patterns in 3D space from quantification of actual behaviors recorded in 306 earlier studies ( [10], [28], [29]). Notably here, the patterns of net contact and flight in 307 the peri-bed net region were accurately reproduced by the model.…”