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Cuticle thickening in a pyrethroid-resistant strain of the common bed bug, study

15 April, 2016
Thick-skinned bed bugs outgunning humans in chemical arms race. By Marcus Strom. smh.com.au. April 14, 2016. There is an arms race between bed bugs and humans, and the bugs are winning. The blood-feeding insects are evolving to survive the chemical warfare we have launched in an attempt to keep our nights bite free. David Lilly at the University of Sydney has found that the outer shells, or cuticles, of these bugs are getting thicker. And bed bugs with thicker shells are highly resistant to the insecticides used to control them. "Bed bugs are well ahead of the curve when it comes to an arms race between us and them," Mr Lilly told the Herald. "Bed bugs have become very well adapted to many of the control efforts we throw at them."
Cuticle thickening in a pyrethroid-resistant strain of the common bed bug, study
Bed bug infestation.Bed bug infestation. Photo: University of SydneyOne way they do this is "metabolic detoxification", where the bugs use enzymes to break down the insecticides."When you have both metabolic detoxification and cuticle thickening there is a synergistic response – you get this two plus two equals five factor," Mr Lilly said. In this scenario, the cuticle slows the insecticide down giving the enzymes more time to act.Westmead Hospital entomologist, Stephen Doggett.Westmead Hospital entomologist, Stephen Doggett. Photo: Wolter Peeters

Out of a sample of hundreds of bugs found in a Parramatta home in 2012, Mr Lilly and his team found that 18 per cent were highly resistant to a pyrethroid-based chemical common in treating bed bugs.This meant that after continual forced exposure to the chemical, they were unaffected more than 24 hours later."It was in this group that we found the thickest cuticle," Mr Lilly said.Common bed bug under an electron microscope. This specimen of Cimex lectularis was found in a Parramatta home.Common bed bug under an electron microscope. This specimen of Cimex lectularis was found in a Parramatta home. Photo: University of Sydney
These resistant bugs had an outer layer that was 15.3 per cent thicker than the susceptible bugs, which were knocked out by the chemicals after two hours.
The study, published today in PLOS One, said this shows that "insecticide resistance is a genetic change … and is considered to be a natural evolutionary response to human-induced environmental stress".Co-author Stephen Doggert, a medical entomologist at Westmead Hospital and the University of Sydney, said: "There is no doubt that the evolutionary adaption times for this species is short." Cross section of a leg of a common bed bug under an electron microscope, showing thickness of cuticle.Cross section of a leg of a common bed bug under an electron microscope, showing thickness of cuticle. Photo: University of Sydney

Mr Lilly said that occurrence of bed bugs is still fairly low, though it’s been a growing problem in Australia and overseas over the past 15 to 20 years.The last time bed bug infestations in NSW had been calculated, in 2006, Mr Doggert said there had been an incredible 5000 per cent increase since 1999, albeit from a low base.Mr Lilly said that infestations seemed to be equally spread in homes and hotels.Lead author David Lilly, PhD candidate.Lead author David Lilly, PhD candidate.
"But you can also find them on public transport or in cinemas where people sit for a long time," Mr Lilly said.One Sydney pest control company contacted by the Herald, Attack Pest Control, said they get calls every day to treat bed bug infestations.A spokesman for the company said that up to 60 per cent of their business was for treating bed bugs. "Over the past four years our calls have doubled," the spokesman said. Life cycle of the bed bug.Life cycle of the bed bug.
Simon Lean is the national technical manager at Rentokil, a national pest control company. He said "frankly, we aren’t run off our feet" with calls for bed bug treatments. Mr Lean said they might be more concentrated in hotels or with travellers as "bed bugs are the world’s best hitchhikers".In efforts to control the bugs, new chemicals have been developed, such as the neonicotinoids. However, Mr Lilly said recent research in the US is already showing bed bugs developing resistance to this family of chemicals."Now that we know the ways they resist control methodologies, we can be a little bit smarter," Mr Lilly said.This can involve non-chemical controls, he said, such as vacuuming before treatment or applying desiccant dust that dry out the bugs, killing them.Heat treatments in furniture can also be used. Bed bugs at all life stages die at temperatures above 45 degrees.If you are infested, there is no shame. Mr Lilly said that bed bugs are not hygiene-related pests."It doesn’t matter whether you have a run-down property or you maintain the most pristine home, you are at the same risk of picking up bed bugs," he said.Mr Lily said the Australian Environmental Pest Managers Association was a good resource for finding a pest controller.You can read more about bed bugs at the university’s  department of medical entomology bed bug website.
_____________________________________________________________________________________________________Journal referenceDavid G. Lilly, Sharissa L. Latham, Cameron E. Webb, Stephen L. Doggett. Cuticle Thickening in a Pyrethroid-Resistant Strain of the Common Bed Bug, Cimex lectularius L. (Hemiptera: Cimicidae)Published in Plos ONE: April 13, 2016http://dx.doi.org/10.1371/journal.pone.0153302

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