Infrared video tracking of Anopheles gambiae at insecticide-treated bed nets reveals rapid decisive impact after brief localised net contact.

Josephine E.A Parker,Catherine E Towers,Natalia Angarita-Jaimes,Mayumi Abe,David Towers,Philip J Mccall

doi:10.1038/srep13392

Josephine E.A Parker, Catherine E Towers + Show 4 more

Open Access

https://doi.org/10.1038/srep13392

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Abstract

Long-lasting insecticidal bed nets (LLINs) protect humans from malaria transmission and are fundamental to malaria control worldwide, but little is known of how mosquitoes interact with nets. Elucidating LLIN mode of action is essential to maintain or improve efficacy, an urgent need as emerging insecticide resistance threatens their future. Tracking multiple free-flying Anopheles gambiae responding to human-occupied bed nets in a novel large-scale system, we characterised key behaviours and events. Four behavioural modes with different levels of net contact were defined: swooping, visiting, bouncing and resting. Approximately 75% of all activity occurred at the bed net roof where multiple brief contacts were focussed above the occupant’s torso. Total flight and net contact times were lower at LLINs than untreated nets but the essential character of the response was unaltered. LLINs did not repel mosquitoes but impacted rapidly: LLIN contact of less than 1 minute per mosquito during the first ten minutes reduced subsequent activity; after thirty minutes, activity at LLINs was negligible. Velocity measurements showed that mosquitoes detected nets, including unbaited untreated nets, prior to contact. This is the most complete characterisation of mosquito-LLIN interactions to date, and reveals many aspects of LLIN mode of action, important for developing the next generation of LLINs.

Highlights

Many of the important mosquito vectors of malaria feed indoors at night, where and when most human malaria is transmitted in Africa[1,2]
Addressing many of the technical challenges that hindered progress to date, we have developed and constructed a novel system that enables tracking, recording and analysis of the flight paths of multiple individual mosquitoes over long periods in the dark at large volumes around the entire human host. In this first application of the system, we describe the flight and landing behaviour of Anopheles gambiae responding to human hosts within bed nets in a large experimental laboratory, and we show that human-baited Long-lasting insecticidal bed nets (LLINs) operate by luring mosquitoes into multiple brief contacts with the net, almost entirely on the net roof, within minutes of commencement of host seeking, virtually eliminating all flight activity by 30 minutes
On detection of a human host within a bed net, mosquitoes responded immediately in four distinct behaviour modes, with persistent attempts to reach the host resulting in multiple brief net contacts focussed on the net roof above the human torso

Summary

Introduction

Many of the important mosquito vectors of malaria feed indoors at night, where and when most human malaria is transmitted in Africa[1,2]. Long-lasting insecticidal bed nets (LLINs) exploit this behaviour and are one of the most effective methods for reducing malaria transmission, fundamental to malaria control (amounting to $2.5 bn in 2013) and to ambitious plans for its elimination[3,4]. Some basic details are missing: e.g. the minimum duration of LLIN contact necessary to deliver an effective dosage is not known Despite these phenomena being recognised for decades[20,21,22], when and how they occur and their relative importance in selecting for insecticide resistance have never been fully elucidated. In the absence of definitions or quantifications of the basic behavioural events likely to be affected[26,27], these changes cannot be investigated, let alone monitored

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