Resistant bed-bugs ‘from tropics’

New results suggest that insecticide use in the tropics is to blame for the re-emergence of bed-bug infestations.

Exposure to treated bed nets and linens meant that populations of bed-bugs had become resistant to the chemicals used to kill them, researchers said.

The findings could help convince pest controllers to find alternative remedies to deal with the problem.

The results were presented at the American Society of Tropical Medicine and Hygiene’s 60th annual meeting.

Since almost vanishing from homes in industrialised countries in the 1950s, populations of the common bed-bug have become re-established in these regions over the past decade or so.

These mostly nocturnal feeders are difficult to control, not only because they are adept at avoiding detection by crawling into creases of soft furnishing but also because they have developed a resistance to many of the chemicals that have been used to kill them.

Findings presented at the gathering in Philadelphia showed that 90% of 66 populations sampled from 21 US states were resistant to a group of insecticides, known as pyrethroids, commonly used to kill unwanted bugs and flies.

Bed-bugs in furniture (Image: Richard Naylor/University of Sheffield)
Female bed-bugs, hidden in furniture creases, can each lay up to 300 eggs


One of the co-authors – evolutionary biologist Warren Booth, from North Caroline State University in Raleigh – explained that the genetic evidence he and his colleagues had collected showed that the bed-bugs infecting households in the US and Canada in the last decade were not domestic bed bugs, but imports.

“If bed-bugs emerged from local refugia, such as poultry farms, you would expect the bed-bugs to be genetically very similar to each other,” explained entomologist and co-author Coby Schal, also from North Carolina State University. “This isn’t what we found.”

In samples collected from across the eastern US, the team discovered populations of bed-bugs that were genetically very diverse.

This suggested that the bugs originated from elsewhere, and relatively recently because the different populations had not had time to interbreed, Dr Schal explained.

He suggested that the source for the new outbreaks was warmer climes, where the creatures would have probably developed a resistance to chemicals.

“The obvious answer is the tropics, where they have used treated bed nets [and] high levels of insecticides on clothing and bedding to protect the military,” Dr Booth told BBC News.

He explained that although bed-bugs were essentially eradicated from industrialised countries in the 1950s, they continued to thrive in Africa and Asia.

“Its very likely that it is from one of these areas where insecticide resistance evolved,” he said.


However, UK-based pest management specialist Clive Boase questioned that hypothesis.

He said bed nets, to protect against mosquito-transmitted malaria and dengue, were only used in parts of Africa that were hot, where the tropical bed-bug (Cimex hemipterus) was found.

But, he added, it was not the tropical bed-bug that was the problem in the US and UK; instead it was their temperate cousin, Cimex lectularius.

Dr Boase explained that comprehensive records showed that infestations of bed-bugs in Europe were less pervasive in the 1970s and 80s, but they were still present.

By continually exposing these populations to insecticides, which came on the market in the late 1970s, these creatures likely developed resistance, he said.

“We don’t have to invoke stories of disease control programmes in Africa; all the evidence here in the UK is that our problem is home-grown.”

Dr Boase wondered that if the US had similar long-term records whether the researchers would have reached a different conclusion.

Evolutionary biologist Richard Naylor from the University of Sheffield agreed: “I am kind of surprised by [their interpretation].

“It doesn’t seem that difficult to develop resistance or lose it; in lab cultures, if you stop exposing [bed-bugs] to pyrethroids it drops out of lab populations very quickly,” he said.

Mr Naylor asked that if the US bed bugs had been exposed to the chemicals elsewhere in the past, “why would they still be resistant?”

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Worms’ sex life yields advantage over parasites

Sex gives worms the power to fight off parasites, report researchers this week in the journal Science.

Worms forced to reproduce asexually succumbed to a nasty bacterial infection and died.

The researchers say the results are the most convincing evidence to date for a key theory in evolutionary biology.

The theory holds that sex evolved because it lets organisms reshuffle their genes into new combinations to stay a step ahead of parasites.

Sex has long troubled evolutionary biologists.

Reproducing asexually – where organisms clone themselves – makes much more sense; there is no need for an organism to search and seduce a mate, fight off competitors, or risk contracting a sexually transmitted disease.

What is more, given that an organism has survived long enough to reproduce, it is likely to have a first-rate set of genes under its pelt.

Why run the risk of diluting these good genes with potentially poorer ones from another organism?

And yet sex exists; the vast majority of animals and plants reproduce this way.

Fluctuating futures

Parasites, many biologists believe, might be the answer.

Parasites create a situation where, in spite of the disadvantages of sex, it is good for an organism to reshuffle its genome with that of another.

This reshuffling creates offspring with new gene combinations that are potentially better than older combinations at resisting a parasite’s advances.

The genetic “arms race” between a parasite and its host is often refered to as an example of Red Queen-style interaction – a term coined by biologist Leigh Van Valen who summoned the image of the constantly running Red Queen from Lewis Caroll’s Through the Looking-Glass.

The analogy seemed to him fitting for describing how species must continually evolve to keep up with each other.

But despite the theory’s popularity, there has been little hard evidence for it.

Out in the field, biologists have noted that organisms are more likely to reproduce sexually when there are more parasites loping around in their vicinity.

What has been missing is a direct manipulation to organisms’ sex lives to test if it makes them more or less resistant to parasites.

Direct evidence

Now researchers working at Indiana University in the US have used the round worm Caenorhabditis elegans to do just this.

The team engineered two types of worms – some that could only reproduce by having sex, and some that could only clone themselves.

The researchers watched the worms gorge themselves on a lawn of a nasty bacterium, Serratia marcescens, which invades the worms’ guts and from there multiplies into every crevice of their body, killing the worms from the inside.

Across five different populations, worms that reproduced sexually fared well over the 20 generations, while all animals that cloned themselves died quickly.

Testing theory

“What is really beautiful about these lab systems is that you can manipulate the system and show that [the theory] can work,” said evolutionary biologist Aneil Agrawal from the University of Toronto in Canada.

Dr Agrawal described the experiment as “elegant” because it allowed the researchers to demonstrate that it was not simply the presence of the parasite that spelled the end for the cloners, but the presence of a parasite that had co-evolved alongside the worms.

To do this, the team created two treatments: one used bacteria from an original stock kept in the freezer, and the other used bacteria that had lived alongside the worms for many generations and so had adapted along with them.

Clonally doomed

In essence, “the bacteria got more and more infective, but the [clonal worms] did not get more and more resistant, and that is why they went extinct,” explained lead author Levi Morran, an evolutionary biologist from University of Indiana in the US.

“I am really excited about this; I think this is really cool,” Dr Agrawal told BBC News.

“Whether this is actually happening in nature is another thing; we can’t know that from a lab system,” he explained.

But he adds that as a first step it is important to demonstrate that under conditions where you expect sex to alleviate the effects of parasites, it does.

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Deepest-living land animal found

Worms have been found living at depths in the Earth where it was previously thought animals could not survive.

Discovered in South African mines, the roundworms can survive in the stifling 48C (118F) water that seeps between cracks 1.3km beneath the Earth’s crust.

The find has surprised scientists who, until now, believed only single-celled bacteria thrived at these depths.

Writing in the journal Nature, the team says this is the deepest-living “multi-cellular” organism known to science.

The researchers found two species of worm. One is a new species to science, which the scientists have named Halicephalobus mephisto after Faust’s Lord of the Underworld.

The other is a previously known roundworm known as Plectus aquatilis.

Until now, only single-celled organisms, like bacteria and fungi, have been recovered from kilometres beneath the Earth’s crust. The lack of oxygen is thought to stymie attempts by anything larger to make its home there.

But this has not stopped scientists looking.

Impossible depths

The Earth’s subterranean world is only accessible to researchers in a handful of places worldwide where ore-mining requires drilling to reach depths of more than 3km.

Taking advantage of two such sites – the Beatrix and Driefontein gold mines in South Africa – the international team of researchers placed filters over the mines’ bore-holes through which thousands of litres of groundwater pour.

From these samples they usually recover only bacteria; so the worms were a surprise.

“It scared the life out of me when I first saw them moving,” said geo-microbiologist Dr Tullis Onstott of Princeton University in New Jersey, US.”They look like black little swirly things,” he added.

These worms seem capable of surviving in very low levels of oxygen – at 1% of the levels found in most oceans, explained Dr Onstott.

But how did the worms get there?

The water in which the worms were found is between 3,000 and 10,000 years old, and so it is unlikely that the researchers brought the worms with them into the mines.

An ancient seep

The scientists, for now, believe that the animals originally came from the surface but got washed down into the cracks in the Earth’s crust by ancient rainwater.

Dr Gaeten Borgonie, a member of research team, explained that he thinks the animals look very much like the tiny worms that live in rotting fruit and soil at the surface, and probably descended from them.

Worms at the surface experience great extremes of temperature and can survive being frozen and thawed, dehydrated and re-hydrated, he told BBC News.

Dr Borgonie believes that worms already have some of the “attributes necessary” to survive at these great depths. So it wasn’t a surprise to him that the first multicellular organism to be found in the deep subsurface of the Earth was a worm.

The authors of the study expect to find other multicellular animals far beneath our planet’s surface, and are preparing to descend again to search for others.

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The Earliest Touchdown

Three hundred million years ago, a flying insect skidded to a landing on a muddy patch of earth and preserved a 3.5-centimeter-long imprint for eternity. From the position of the legs, the curve of the abdomen, and the lack of wing marks, the researchers suspect that the imprint was made by an ancient mayfly that held its wings upright when at rest. Collected in southeastern Massachusetts, the fossil is the oldest known full-body impression of a flying insect, the team reports online today in the Proceedings of National Academy of Sciences. The ability of today’s insects to skim the surface of water is thought to be a modern invention. But the discovery of tiny drag marks (see inset) that suggest that mayflies likely slide before stopping is at least enough to prompt some paleontologists to keep an open mind on the matter.

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Worms Are Divided After All

It turns out that worms really are deeply divided. In the mid-19th century, French naturalist Jean Louis Armand de Quatrefages de Bréau split worms into wigglers—which crawl and swim to their hearts’ content, such as the marine ragworm (left)—and the more sedentary, typically tube-dwelling nonwigglers, such as the earthworm (right). However, early genetic studies called this classification into question. They indicated, for example, that the wigglers weren’t that closely related to one another; instead, their physical similarities were the result of their adapting to similar lifestyles and environments. Now more comprehensive genetic evidence, reported online today in Nature, shows that de Bréau was right after all. Analyzing 231 genes from 34 different annelids, otherwise knows as ringed worms, researchers have shown that wigglers and nonwigglers do indeed represent two different evolutionary groups. What’s more, the team found that the split between the two groups happened very early in worm evolution; the exact date isn’t known because the soft bodies of worms don’t preserve well as fossils. Wigglers kept their bristled appendages for moving around and foraging, whereas nonwigglers lost them as they evolved to stay put in their burrows to eat sediments and plankton.

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A Spider That Likes Stinky Socks

Arachnophobes everywhere will be heading to the laundromat when they hear this. Researchers have found that an East African spider, Evarcha culicivora, is attracted to your stinky socks. By presenting the spiders with a pair of socks worn continuously for 12 hours and a pair of identical unworn socks, researchers showed that the arachnids prefer the smell of human feet. Luckily for us, it’s likely that the spider’s odor detection has evolved not to find humans, but rather to catch the mosquitoes that carry our blood, researchers report online today in Biology Letters. Still, it might not be a bad idea to take your socks off before bed.

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Parasite Invasion Caught on Camera

For the first time, the tiny malaria parasite, Plasmodium falciparum, has been caught on camera breaking and entering a red blood cell. High resolution 3D images reveal that once the three components of the parasite—nucleus (blue), other organelles (red), and the green pore the parasite brings with it and through which it invades (green)—have attached to the cell, a switch is triggered and the parasite is free to burrow through the cell’s membrane. From this point on, the parasite is unstoppable, multiplying within the cell until it breaks out of its host to invade fresh red blood cells. The new imaging technique will allow researchers to see the effects of novel drugs on this final stage in the parasite’s invasion strategy, researchers report online on this week in Cell Host & Microbe. They hope that this will help scientists develop better drugs to alleviate the suffering of the 400 million people who contract malaria each year.

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Sleepy Bees Lose Their Rhythm

Sleep deprived and having trouble communicating? You aren’t alone. Drowsy honey bees (Apis mellifera) are incoherent, too, researchers report online today in the Proceedings of the National Academy of Sciences. Every morning, the bees set off on their daily foraging trips and return to the nest to perform a waggle dance. The angle of the bee’s body relative to the sun indicates the direction its comrades must fly in to find the good flowers, and the duration of its dance tells how far away they are. Sleep-deprived bees—kept up all night by researchers agitating them—made more errors when communicating the direction of the flower than did well-rested bees; at least until they had caught up on their sleep. Experiments to demonstrate whether bee insomnia is bad for the colony’s survival are underway; until the results are in, worker bees are advised to be tucked up in a hive, with a hot cup of nectar by 9 p.m.

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Whistling Caterpillars Shake Off Predators

When in danger, whistle. It works for the walnut sphinx caterpillar (Amorpha juglandis). The fat, juicy larvae of butterflies and moths tend to be experts at predator avoidance, using camouflage, rolling themselves in leaves, and even flicking their own poop to discourage birds, frogs, and small mammals from eating them. Whistling is just another string in their bow, researchers report online this week in The Journal of Experimental Biology. When the team used forceps to simulate the peck of a bird’s beak, the caterpillars forced air through the small holes on either side of their body—normally used for breathing—to produce a high-pitched whistle. When yellow warblers heard the noise, these natural enemies of the caterpillars hesitated, jumped back, or flew off. The sound may have startled them, or perhaps they found the tune indigestible.

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