The biteOscope: studying mosquito feeding
There are thousands of species of mosquito, all with their own patterns of feeding behaviour, things that they are repelled by or attracted to, and diseases that they can carry. Studying them consistently, and realistically, is therefore a challenge. But now Felix Hol, from the Institut Pasteur in Paris, has come up with a gadget that he calls “the biteoscope”. As he told Chris Smith, this is an apparatus that’s home to a hoard of hungry mosquitoes and a patch of synthetic skin containing a blood-like fluid; there’s a camera below the skin patch hooked up to a computer to document how the insects behave…
Felix - We now just use basically the thing that's most easily thought of as synthetic skin. So basically just a fake human mimic. To us it just looks like a piece of plastic, but we treat the piece of plastic in such a way that mosquitoes find it attractive enough to find it, land it and bite it. We, for instance, heat the substrate close to body temperature, which is a very strong guiding cue for mosquitoes. We also can spray in CO2, which is normally in our exhaled breath and that activates the mosquitoes to start searching for a host. So we can guide the mosquitoes towards this little device and there they land on a membrane, and the mosquitoes actually need to pierce through a surface in order to be able to feed. They insert their mouth parts and here they find an artificial meal that is transparent. It has basically essential qualities of blood that make the mosquito think it is like blood, and they actually engorge as if they would be drinking blood.
Chris - Where's the camera then? Is that underneath that transparent membrane so that you're basically seeing the mosquito from underneath as it lands and then tries to feed?
Felix - Yes, this is exactly right. So the mosquitoes are just contained in the cage and in the floor of that cage, we have the bite substrate up. We can just image through the bite substrate while they're feeding on the substrate
Chris - And that data, that's all going into a computer, does this mean that you can basically use image analysis on it so that rather than you painstakingly picking apart what the mosquitoes are doing, timing how long it does each step, you can get a computer to do that? So you can do this potentially at enormous scale, cause you could study loads of mosquitoes without actually having to do anything yourself?
Felix - Exactly yes. So we developed a lot of algorithms, a lot of custom software that picks out the mosquitoes in those images - where it was, how long it was walking on the substrate, when it starts biting the substrate. And from those images, we can also obtain things like how much does their abdomen swell. So of course their belly swells while they're drinking and from how much the belly swells, we can actually calculate whether or not it's drinking and whether it gets fully engorged or not. You can track exactly where all the legs are going, where the mouth parts are going, where the head is. And from that, we can basically calculate the relative positions of the body parts.
Chris - Do you think the mosquitoes are actually fooled by this system though? Do they actually really regard this as skin and are they behaving in a way that you think is exactly the same as they would were it your arm in there for real?
Felix - So I do think that indeed they're fooled. They binge on this artificial meal, they drink a lot of it. They swell three times their volume. So in that sense, they're clearly fooled at the moment. We don't really know what the relative attraction of our substrate is compared to a human arm. I mean, that would be an interesting follow up experiment to do at some point where basically we present a real arm to the mosquitoes, and we present our substrate and we look at whether they prefer the arm over our substrate, or maybe the other way around
Chris - Now you've got this working, have you actually begun to gather data from it yet that are highlighting things that we previously, because of the constraints, the way we've historically tried to study mosquito feeding behavior, had overlooked?
Felix - Yeah. So there's one example in the study that Anopheles coluzzi that is a mosquito species that is an important malaria vector in Africa. People had known for a long time that it is rebelled by the mosquito repellent DEET. However, the mode of repellency was not entirely understood. And in this study we actually show that the mosquitoes senses it with their legs. We could coat a small portion of the bite substrate with this insect repellent. And when they land just outside of their coated area, we see that they just walk around and have their normal behavior. Whereas when they land in the coated area, they immediately take off right after their first touch. So from this we learned that actually the mosquitoes are likely tasting this repellent with their legs and are using that information to leave. And I think in the future there's many different things that we can do in this setup. For instance, one thing that I'm very excited about is to compare the behavior of mosquitoes that are infected with a pathogen, for instance, dengue virus or malaria parasites, versus the behaviour of mosquitoes that are not infected with anything in the literature. There are certain reasons to think that infected mosquitoes actually may behave differently. Maybe they're more avid or less avid to feed. Possibly the infected mosquitoes will take a smaller blood meal and therefore maybe actually will need to bite more often and therefore actually infect more people. These things are fairly difficult to measure because it's pretty difficult to do experiments on infected mosquitoes. I really think that with the BiteOscope, we will actually have a really cool angle on that and see if they actually behave differently.