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BiteOscope: an open platform to study mosquito blood-feeding behavior

Felix JH Hol, Louis Lambrechts, Manu Prakash

Preprint posted on February 20, 2020 https://www.biorxiv.org/content/10.1101/2020.02.19.955641v1

BiteOscope: a novel tool and a spy-glass into mosquitoes' lives and behaviour.

Selected by Mariana De Niz

Background

            Female mosquitoes of various species are hematophagous, and need a blood meal to reproduce. This need constitutes the basis for the interphase between mosquitoes and mammalian hosts, which unfortunately provides an opportunity for mosquito-borne pathogen transmission. Pathogens transmitted by mosquitoes include viruses- causative of a wide range of diseases including dengue, Chikungunya, Zika and West Nile fever among others, and parasites, also causative of a range of diseases, including lymphatic filariasis, and malaria. The latter alone, is considered one of the heaviest public health burdens in terms of morbidity and mortality.

Although various landmark studies have investigated odours attractive to mosquitoes, and the steps following pathogen injection into the skin, overall, many aspects of blood feeding remain poorly understood. It is known that upon landing, mosquitoes exhibit exploratory bouts by making contact with the legs and proboscis on the skin, and it has been suggested that these appendages play an important role in evaluating the skin surface for bite-site selection. Furthermore, we know that various parts of the proboscis also serve as chemosensory organs, potentially guiding blood-feeding – however, the mechanism for this remains unknown. In this study, Hol et al present the BiteOscope, an open platform that attracts mosquitoes to a host mimic, which allows high resolution and high throughput characterization of mosquito behaviour during feeding including surface exploration, probing and engorgement (Figure 1).

 

Figure 1. BiteOscope design (top), and identification of key mosquito behaviours through investigation of specific body parts.

Key findings and developments

            Altogether, the authors used the BiteOscope to investigate the behaviour of various mosquito species, including those of clinical importance, namely Aedes aegypti, Aedes albopictus, Anopheles coluzzii and Anopheles stephensi. The BiteOscope consists of a rudimentary skin mimic composed of a substrate that attracts mosquitoes to its surface (via a heat source), induces landing, piercing, and engaging in blood feeding – the latter, by using (or not) adenosine triphosphate as a strong phagostimulant. This substrate can be mounted in ways such that free behaviour of mosquitoes is maintained. The substrate is transparent, which facilitates imaging of mosquito interactions, and skin piercing. The authors adapted illumination according to the mosquito species and their preferred feeding time, namely white light illumination for Aedes spp. (which are known to bite preferentially during daylight), and infrared light for experiments involving Anopheles spp. (known to preferentially feed at night time).

The authors also developed computational tools to extract behavioural statistics (i.e. locomotion and engorgement) from the images obtained, as well as and machine learning (based on DeepLabCut) to track individual body parts of behaving mosquitoes – focusing on the head, proboscis, abdomen, abdominal tip, and 6 legs. They described body positioning during three main behaviours in Aedes albopictus mosquitoes: anterior grooming, walking and probing.

The authors then went on to characterize mosquito behaviour upon the use of DEET. Although DEET is a well-known insect repellent, its mode of action is poorly understood. In their work, the authors showed that repulsion of A. coluzzii mosquitoes occurs upon contact with the legs. The authors discuss the potential of the BiteOscope to enable studies that allow us to further understand external (environmental) and internal (physiological) aspects of blood-feeding behaviour.

What I like about this preprint

                  As for most of the preprints I choose, I like a) that this is open science that provides all the details necessary for adaptation and replication of studies, and b) that it identified and bridged a gap, through tool-development, of important biological questions relevant to vector-borne pathogen transmission. I think it’s an out-of-the-box approach, and complements other pieces of the same puzzle across various fields of research (eg. virology and parasitology). Only recently, interest in understanding the skin as an interface for pathogen transmission has gained momentum, and having a toolbox to move forward in our questions is key. This work provides what I believe is one important tool.

References

  1. Hol FJH, Lambrechts L, Prakash M, BiteOscope: an open platform to study mosquito blood-feeding behavior, bioRxiv, 2020

 

Posted on: 21st May 2020

doi: https://doi.org/10.1242/prelights.20943

Read preprint (1 votes)




  • Author's response

    Felix JH Hol shared

    Open questions 

    1. This is a very exciting tool, opening many possibilities. You included already, various elements affecting mosquito behaviour (eg heat and light). Can you add odours to the substrate, to complement the known attractants? Can you simultaneously use various substrates with different properties to determine mosquito behaviour upon provision of choices (decision-making)?

    Those are all interesting suggestions! The short answer is yes/we’re working on it. There is lots of literature regarding which odourants attract mosquitoes to humans. Luckily, many of those odorants are commercially available and can be used to coat surfaces and/or be diffused into a cage. We are currently working on this.

    Making a `choice assay’ is another interesting option. We have some preliminary results with this, and it is indeed possible to present and evaluate multiple bite substrates in the same cage. One caveat is that this requires a larger field of view and as a consequence it becomes harder to resolve tiny details in the images. Despite this, it’s an interesting opportunity for future research.

    2. You work can easily be adapted to other vectors which are important sources of pathogen transmission like tsetse flies, sandflies, and triatomine bugs. The behavior of those vectors during the interaction with the skin is also incomplete. Are you planning to adapt the BiteOscope to study other vectors?

    That would be an amazing thing to do. We have some colleagues that work with tsetse flies and sandflies and it would be wonderful to translate our tool to other vectors. It would be great if interested researchers would get in touch about adapting the biteOscope to their experimental systems.

    3. Also related to decision-making, there have been studies showing differences in attraction to different animals. Can you adapt the skin mimic accordingly, to simulate skin of different animals and observe feeding preferences? This might shed light into transmission and non-human reservoirs of pathogens.

    That would be a very interesting thing to do. I can imagine that odorants differ quite a bit between different host species, and also the texture of the skin — fur, feathers, etc. It would be interesting to combine our approach with fabrication methods that mimic different textures and see how that affects blood feeding.

    4. Have you planned on using the skin mimic to study pathogen transmission “the other way around”? Namely, adding parasites to the substrate, and observing mosquito behavior upon uptake of pathogens?

    Yes, that is something we’re very interested in. Likely, we would not add the pathogen to the substrate directly as we expect the effects of pathogen infection to become apparent a while later (when an infection has been established in the mosquito), yet we are very interested in using the biteOscope to compare the behavior of infected and non-infected mosquitoes. I hope our method will be useful to decipher the effects of pathogen infection on mosquito behavior.

    5. You mention in your work that the richness of data you obtained from imaging multiple mosquitoes (i.e. exploiting the value of high-throughput) allows quantitative characterization of individual behaviours hidden in population averages. Can you expand further on this point, and why this might be relevant to our understanding of mosquito-mammal interactions and pathogen transmission?

    There are many possible answers to this question, depending on what you’re interested in and what you decide to measure/analyze. In general, I believe that while population averages are very useful, they hide the underlying distribution. For instance, the population fraction that fully engorges is often the outcome of a blood feeding experiment, however, this does not provide information about how many bites individual mosquitoes needed to come to full engorgement. From modeling studies we know that the number of (potentially infectious) bites is a very relevant parameter to estimate the transmission of disease. We anticipate that our method will enable detailed measurements like this. 

    6. Have you thought of integrating to your setup, another tool which allows imaging and study of the mosquito brain during behavioural experiments, and how signals might be integrated during visual and olfactory stimulation – which you provide with your skin mimic?

    There are several labs that have the capability of imaging the mosquito brain while presenting different stimuli and I think this is a very important tool to better understand the sensory neurobiology of mosquitoes. Incorporating something like that in our current set up would be very challenging as brain imaging typically is performed on immobilized mosquitoes, whereas mosquitoes are allowed to move in our set up. However, who knows what the future will bring….

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