Researchers at the Liverpool School of Tropical Medicine (LSTM) have tracked mosquitoes to observe how they interact with insecticide-laden nets. From a Sept. 1, 2015 LSTM press release (also on EurekAlert),
LSTM vector biologists Dr Philip McCall and Ms Josie Parker worked with optical engineers Prof David Towers, Dr Natalia Angarita and Dr Catherine Towers from the University of Warwick’s School of Engineering to develop infrared video tracking technology that follows individual mosquitoes in flight as they try to reach a human sleeper inside a bed net. This system allowed the scientists to measure, define and characterise in fine detail, the behavioural events and sequences of the main African malaria vector, Anopheles gambiae, as it interacts with the net. Funded as part of the €12M AvecNet research consortium, the team’s initial results are published today in the journal Nature Scientific Reports.
Dr Philip McCall, senior author on the paper, said: “Essentially, the results demonstrated that an LLIN [Long-lasting insecticidal bed net] functions as a highly efficient, fast-acting, human-baited insecticidal trap. LLINs do not repel mosquitoes – they deliver insecticide very rapidly after the briefest contact: LLIN contact of less than 1 minute per mosquito during the first ten minutes can reduce mosquito activity such that after thirty minutes, virtually no mosquitoes are still flying. Surprisingly, mosquitoes were able to detect nets of any kind while still in flight, allowing them to decelerate before they ‘collided’ with the net surface.”
The use of this innovative approach to mosquito behaviour has provided unprecedented insight into the mode of action of our most important tool for preventing malaria transmission, under conditions that are as close to natural as possible. The findings potentially could influence many aspects of mosquito control, ranging from how we test mosquito populations for insecticide resistance to the design of a next generation of LLINs. An MRC Confidence in Concept grant has funded the team to use the tracking system to explore a number of novel LLIN designs, already patented as an outcome from the current research.
The tracking system also has been deployed in a rural Tanzania, results of which will be reported shortly. The team recently was awarded £0.9M support from the Medical Research Council (MRC) for the next stage of this project, where they will use a larger three-dimensional system to track mosquitoes throughout the entire domestic environment, in experimental houses in Tanzania.
Dr McCall continued: “preliminary results in field tests indicate that these laboratory findings are consistent with behaviour of wild mosquito populations which is very encouraging. We are at the early stages of this research, but we hope that our findings, and the use of this cutting edge technology, can contribute to the development of new and advanced vector control tools that will continue to save lives in endemic countries throughout the world.”
The fascinating part follows the link to and citation for the paper,
Infrared video tracking of Anopheles gambiae at insecticide-treated bed nets reveals rapid decisive impact after brief localised net contact by Josephine E.A. Parker, Natalia Angarita-Jaimes, Mayumi Abe, Catherine E. Towers, David Towers, & Philip J. McCall. Scientific Reports 5, Article number: 13392 (2015) doi:10.1038/srep13392 Published online: 01 September 2015
This open access paper provides an explanation for why this work was undertaken,
Delivering the ‘next generation’ of LLINs or similar tools will require a thorough understanding of how LLINs function, yet remarkably little is known of the mode of action or of precisely how mosquitoes behave at the LLIN interface. Recent studies using ‘sticky-nets’ reported that host-seeking female Anopheles spp. landed preferentially on the top surface of bed nets7,8 but that lethal capture method recorded only a single landing event and no other behaviours before or after. Although clustering at the net roof is likely to be a response to an attractant ‘plume’ rising from the human beneath [emphasis mine], this too remains speculative because knowledge of mosquito flight behaviour prior to blood-feeding and of the identity and location of the key attractants that mediate the host-seeking response is limited9,10,11,12. Importantly, how insecticide treatments influence that response is unclear. Some studies reported that insecticide residues repelled mosquitoes prior to contact13,14, which would reduce or eliminate the chance of mosquitoes receiving an effective dose and potentially divert them to unprotected hosts15. Others found no evidence for such repellency16,17,18,19 indicating that LLINs attract and impact on mosquitoes by direct contact.
A further complication is the existence of what is termed ‘contact-irritancy’ or ‘excito-repellency’ [emphasis miine], whereby brief exposure to an insecticide can result in mosquitoes exhibiting avoidance behaviour, potentially before a lethal dose has been delivered13,20. Remarkably, 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 decades20,21,22, when and how they occur and their relative importance in selecting for insecticide resistance have never been fully elucidated.
Consequently, behavioural resistance [emphasis mine] to insecticides remains poorly understood and rarely reported in mosquitoes, though the risk of vector populations switching blood-feeding times, locations or host preferences in order to avoid LLINs is recognized and closely monitored today23,24,25. However, additional but less apparent or detectable behavioural changes also might exist, potentially conferring partial or complete insecticide resistance (e.g. changes in sensitivity to repellents, attractants, or modified flight or resting behaviours). In the absence of definitions or quantifications of the basic behavioural events likely to be affected26,27, these changes cannot be investigated, let alone monitored.
I am fascinated by the ‘attractant plume’, ‘excito-repellency’, and the (new to me) notion that mosquitoes can exhibit behavioural resistance.