Bed Bug Biology

本,臭虫是一个很小的几个之一species who demonstrate an unusual type of mating behaviour known as "traumatic insemination". This is where the male, rather than delivering sperm into a specially evolved organ actually pierces the abdomen of the female and delivers the sperm directly into her abdominal cavity. To explain more about the biological adaptions that allow a female to survive this, we are joined by Dr. Richard Naylor who works with the Bed Bug Foundation. Richard, thank you for joining us. This doesn't sound like a very efficient or effective way of inseminating...

丰富的ard - It's not at all efficient or effective for the female. Well, it's effective. They do have offspring as a result of it, but it's not the female that drive it.

Ben - What actually happens? Once the male has punched his way through and delivered his sperm, presumably there are specialised organs then within the cavity that take the sperm to the right place. He can't just make a hole wherever he wants it and the sperm just finds its way to an egg or can it?

Ben - So, from the male's perspective, he can just deliver his sperm as and where. If there are sperm storage organs then that like in many other insects would imply that you can get multiple matings. Does this mean the female actually gets stabbed many times and then selects out the sperm that she wants to use?

丰富的ard - There's no evidence to show that the female can select which sperm she wants to use, but you're absolutely right. There are multiple matings upon multiple matings. The males, we know, mate tens and tens of times more frequently than females need to be mated in order to stay fully fertile. So, we know that this is bad for females because the males are just mating far more than they need. A female bed bug needs to mate about once every 5 weeks and it's likely to be 5 or 10 times a day that the males will mate with the females if they get the chance.

Ben - How do the females actually survive this? Well, the clue is in the name, isn't it? It sounds traumatic.

丰富的ard - It is traumatic. We know that they don't survive as well as they would if they were only receiving mating every 5 weeks. We've done these experiments and we've shown that females pay a cost in terms of their longevity, their lifespan of about 25% as a result of natural mating rates. So we know that this mating system is bad for females, but they don't have any control over it. It's a male-driven mating system, so the males impose the mating rate on the females.

Ben - I mentioned at the beginning that there are not very many species that actually undergo this and I can see why. What is the sort of selective pressure that caused this to evolve? You would think as it is so costly for the females that it would very quickly adapt out.

丰富的ard - Yeah, that's right. If you imagine a biological system where males and females are working together to produce the most offspring between them, you would expect it to adapt out as you say. But that's not what we think is happening. We think there's a conflict between males and females and what's in it for the males is that it's always the last male that sires the most offspring. And so, males are competing to be the last one and that's what's driving this elevated mating rate.

Ben - Now we also mentioned earlier that there is, of course, as with any injury there is a risk of infection. What adaptations do the females have in order to be able to heal, to repair the wound, and to stop themselves just being taken over immediately by a bacterial or fungal infection?

丰富的ard - Well, in the bed bug, there's a very similar system in the whole family, the Cimicidae and they all showed different levels of adaptation. But in the bed bug, the females have a little pocket which receives the sperm, this little pocket is called the spermalege, and it's packed full of immune cells, something like our white blood cells has a very high concentration of them in this little area. It looks like a little patch of cotton wool and it's probably about the size of a large grain of brown sugar. This little area of immune cells does a very good job at mopping all those bacteria and also, stopping hemolymph from leaking back out through the wound that the males make.

Ben - Now, species like bed bugs have just what we call an innate immune system. So, unlike our immune system which can learn to recognise a threat and then adapt, and then the next time you get infected with the same bug, you are even better at fighting it off. With just the innate system that they have, presumably, it must be really quite aggressive to just fight and kill off everything.

丰富的ard - We've always thought about insects as having very basic, simple, and not very advanced immune systems and to some extent, that's right. But it is a very effective immune system. It has several different components to it and one of the most important components is lysozyme. It releases lysozyme and this chops up bacteria. It can detect bacteria being introduced and then elevate these various components of its immune system and just fire all these toxic chemicals at the bacteria and hopefully wipe them out. In the bed bug, it does a pretty good job in that immune organ.

Ben - So, does that mean that there's something that we can learn from the bed bugs about potentially how to fight off infections or to make new antibiotics?

理查德-抗菌肽是th之一ings that insects have that we've been exploring as a medication. What's interesting about insect immune systems is that bacteria don't seem to evolve resistance to them. So we've all heard of antibiotic resistance, which is rendering all of our antibiotics that we use in the medical profession useless because the bacteria are evolving to cope with them. And we don't see nearly as much resistance to antimicrobial peptides which is one of these tools that the insects use. So yes, there are lots of people working on that very question - can we learn from insects to help ourselves?

Mimicking human organs and diseases in the lab could help to investigate diseases and rapidly screen compounds to find new drugs, and now, researchers at the Wyss Institute for Biologically Inspired Engineering at Harvard University have made a lung-on-a-chip capable of modelling a human condition called pulmonary oedema.

The lung-on-a-chip device itself was first demonstrated two years ago by the same team, led by Donald Ingber, founding director of the Wyss Institute. It consists of a polymer structure about the size of a USB memory stick, containing a number of hollow channels. Two of these channels are separated by a porous membrane, which is coated on one side with human lung cells, and the other with cells from very small blood vessels known as capillaries. By passing air over the upper surface and blood-like medium over the underside, this chip can model interactions that occur at the surface of the lung. Two other channels on the sides of the chip can expand and contract to deform the interface to mimic human breathing.

This new research, published inScience Translational Medicine, demonstrates abnormal function of a human lung. A drug used in cancer chemotherapy, interleukin-2 (IL-2) is known to have a serious side effect of causing pulmonary oedema, where fluid can leak into the air spaces in the lungs. If the lung-on-a-chip is truly modelling a human lung, we should see leakiness across the lung tissue as a result of administering IL-2.

This was exactly what they saw. At similar doses and over similar time frames, the lung-on-a-chip experienced the leakiness, reduction in oxygen transport and clotting of an oedema patient. The experiment went one step further and identified something completely novel about oedema - the very act of breathing increases fluid leakage over three-fold.

Organs-on-a-chip can be used for very high-throughput, replicable and controllable drug screening - potentially doing away with the need for some animal studies and increasing the rate at which we can identify new drugs. To find out is their model could work in this way, the team then tested potential therapeutic agents, including a new class of drug called a Transient Receptor Potential Vanilloid 4 (TRPV4) channel blocker being developed by GlaxoSmithKline. The team found that the symptoms in the lung-on-a-chip were prevented by this drug, a result that fits well with GSK results from mouse models.

这给了我们信心lung-on-a-chip,苏ggesting it really is acting as a genuine organ might, at least when it comes to pulmonary oedema. Other organs, organ systems and other conditions, should follow and will likely change the future of drug discovery and testing.

In Fairy-wrens (Malurus cyaneus), hungry chicks need to give a password to get food from their mother, and research published in Current Biology shows that they learn this password while still in the egg.

t's important for a Fairy-wren to recognise its own young because they are subject to parasitism by cuckoos - in particular the Horsfield's bronze-cuckoo. Adult cuckoos lay their eggs in fairy-wren nests, and leave the young to be brought up by the wren. A developing cuckoo chick will eventually throw all of the other chicks from the nest, meaning that all of the wren's resources go into bringing up someone else's offspring. This is hugely costly, so the wrens have evolved a range of behavioural and acoustic ways to cope.

Sonia Kleindorfer at Flinders University and colleagues in America and Austria monitored 15 nests for the entire nesting period, recording all of the wren songs. They discovered a previously unknown vocalisation, now called the incubation call, which females only used when they were alone and incubating their eggs - stopping as soon as the eggs hatched.

They also recorded the young after they hatched, and were particularly interested in the calls made whilst begging for food. Noticing significant differences between different nests, they then compared the begging calls with the incubation calls from the same nest, and found a shared audio "signature" in both types of call.

This could indicate that the call is learned while still in the egg, or may be genetically hard-coded into the chicks. To find out, they did a series of foster-parent experiments by swapping complete clutches of eggs into unrelated nests and looking for similarities in vocalisations. They found that the similarities were significantly greater for parents and their foster chicks than for genetically related animals incubated by a different mother, reinforcing the idea that these signatures are learned, rather than inherited. Further evidence comes in the fact that similarity between mother and parent was related to how frequently the mother called during incubation - a dose-dependent response, to use medical terminology.

The research didn't entirely rule out a genetic component, as certain elements in the song showed similarities with biologically similar but fostered animals, hinting that genes still play an important role.

Playback experiments then confirmed that hearing this password did cause adults to behave differently towards the offspring, and were far more likely to abandon a brood that didn't use this signature in their calls. Females were also recorded calling to males to solicit food, and including the same signature as in their incubation calls. The males also seemed to learn the password, and would adapt their behaviour accordingly by, for example, reducing feeding rate when exposed to calls that didn't match.

研究人员认为,当布谷鸟鸡蛋添加ed to the nest at a later stage than the wren's own eggs, they are therefore exposed to fewer incubation calls, and have less opportunity to learn to mimic the mother. Kleindorfer and colleagues argue that this gives the wrens an advantage against the cuckoos in an acoustical arms race, and help to avoid wasting resources bringing up an unrelated chick.

克里斯,我们听到臭虫感染病例d are on the rise, but how do you know you've actually got them and what can you do if you have got them? Clive Boase is from the Pest Management Consultancy. Hello, Clive.

Clive - Yeah, good evening.

Chris - So, tell us then, how do I know I've got bed bugs in my house? I mean, I haven't. I've done it before I'm done with my mortgage value of my property, but would I know?

Clive - Not surprisingly for blood-feeding insect, the first time you'll get of an infestation or the first time that most people get is the appearance of bites, and as we've heard earlier, these can be really quite unpleasant, red, itchy lesions. They could appear anywhere on your body, but most typically, they're on those parts of your body which are out of the covers when you're sleeping at night. So, it's going to be the neck and the shoulders and perhaps the sides of your face, maybe the arms; those parts of you that aren't covered up when you're in bed. Now of course, the trick is to recognise these as insect bites as opposed to some other kind of skin disorder. Many people we meet, their story running into a bed bug infestation is to say they had a skin condition. They put it down to maybe some kind of eczema or allergy, they treated it, and often, it's not until a few months later, 3, 5, 6, 7 months later that by some chance situation, the home owner actually spots insects in the bed and draws the connection between this hither-to eczema-type skin condition in the insects and realising it's not a skin condition at all. It's actually bites from the bed bugs. Bed bug awareness on the part of homeowners generally is perhaps one of the most important things that we've done to speed up the identification of individual infestations and as a result of that, the treatment and elimination of them.

Chris - So what advice can you give people about not bringing them home from their holidays?

Clive - If you're staying in a hotel or any other kind of accommodation away from home, then be aware of bed bugs. The chances of picking up bed bugs is actually very, very small. You know, I really wouldn't want to give the impression that the hotel industry in this country or any other country is awash with bed bugs. They're not. The figures we have show that the percentage of rooms affected by bed bugs are really very, very small, less than 1 in 1,000, sometimes down to 1 in 10,000.

Chris - How do you know that? Do you have to go and sleep in the bed and see if you get bitten?

克莱夫——不,我们从酒店和收集统计信息as I said, contrary to popular opinion, bed bugs are really not that common in hotels despite what you read in the newspapers. The most important things to protect yourself are; be very aware of buying second hand bedroom furniture. Think again about that second-hand mattress. Think about that second hand bed or that bedside table that you're thinking you might buy. Bed bugs are very commonly moved around on those sorts of items, so be aware of that. And again, don't move into premises where there are bed bugs. If you're thinking of renting a bed set or a flat or somewhere, have a look for signs of bed bug infestation. What we're looking for are the faecal spots of bed bugs. As we've said, bed bugs feed on blood, their faeces are very dark coloured, and typically, what we'll see is numbers of small dark spots, perhaps the size of a pinhead, maybe a millimetre across or so around bed bug harbourages and as Toby said, those harbourages maybe on or around the bed. So we might be looking for the beading around the mattress, around the buttons on the mattress, around joints in a wooden bedframe, where the skirting board joints along the wall, if you've got a white skirting against the wall, if we've got little bits of lose wallpaper, a back of the headboard will be the classic sign. So, if you're thinking of renting a furnished flat, a furnished bet set, have a look at those sorts of areas and if we're seeing little black spots around there, then be very, very careful.

Chris - So, if someone calls you in and you have a look at the bed and you see these black spots and that's the danger sign to you, what do you then do, tear the room apart to see if you can find them? What do you do?

Clive - In order to start a treatment programme, we really need to confirm that they really are there. We don't need to find every last one. We're just looking for enough of a sign to say, "Yup! The room is infested." And then a bed bug treatment programme might start.

Chris - Just in one room or does that mean, you got to blitz the whole flat or the whole house, or whatever?

Clive - Bed bugs as we've heard are really quite mobile and if we've got a typical 2, 3-bedroom house, if they're in one room, the chances are, they're in another. So, don't stop at the first room where the original sighting or the original concern is raised.

Chris - I mean, if you live in a block of flats or maisonette or something, if someone downstairs has got them, could they crawl up into your flat?

Clive - Yeah, absolutely they could. This last week, I've been working a number of premises doing research work there and there, in blocks of sheltered accommodation, we're finding individual flats that are if you like, a focus flat that is really quite heavily infested. Then around that, we have a number of adjoining flats, not just adjoining on one level, but above and even below as well as you say, where we're finding lighter bed bug infestations. The indication is that bed bugs are spread from that original focus flat. In some cases where we've got really heavily infested flats, if we step outside of that flat into the corridor, and we can see actually bed bugs in the corridor around the door frame, perhaps around the lights on the ceiling in the corridor, and then even when we turn around 180 degrees from that badly affected flat and into the flat opposite, lo and behold, we find a few bed bugs in there. So, they will - we talked earlier, I think Toby talked about passive dispersal of bed bugs, but active dispersal between blocks of flats is really very, very important. And it's something, I think going back a few years, perhaps we didn't realise it happened to the extent it really does. We didn't think bed bugs are particularly mobile. Now, we realise they are.

Chris - What about getting rid of them? Once you've found them, you've identified positively that they're there, how do you get rid of them?

Clive - There's a number of options. There's the do-it-yourself option. There's not an option I'm in favour of. Again, when I get involved with people with bed bugs, there'll be this typical narrative history where eventually found they've got them. They will have tried to get rid of them themselves and they will tell me about, "Yes, we bought some aerosols. We bought some powder. We threw away the mattress. We got a new bed. We threw away the carpet and so on". After having done all that, they still got bed bugs. So, I would say that anybody who believes they've got bed bugs, they need professional advice and that professional advice may be input from a local authority pest control team, and there's still numbers of local authorities that offer pest control service, or a private company. And I think the important thing is to talk with a number of potential providers of the service, check out the service they can provide, check out the costs. Very importantly, ensure that they will guarantee they work, so it doesn't get a result, they will come back and do it again.

丰富的ard - No, it didn't preceded it. It came secondarily. Bed bugs do have a normal reproductive tract through which they lay their eggs and this is a way of the males bypassing the normal route to try and get more of the offspring for themselves.

Toby - It depends if you've got a super-hot electric blanket, but no.

Chris - A serious electric blanket, wouldn't it?

Toby - Yes, exactly!

No, they're quite happy at the temperatures an electric blanket would have. In fact, one of the hypotheses is that central heating - keeping the house a certain temperature - has actually helped them. They don't die off in the winter, which they might have done back before we could maintain a constant temperature.

I don't think an electric blanket would have the best thing for you!