Researchers at the University of Sydney have discovered that bed bugs showing resistance to commonly used insecticides have thicker skins than those that are rapidly killed by chemical treatment. This could be one reason why the blood-sucking pests are becoming more common (Lilly, 2016).
After several decades when an encounter with a bed bug was a rare experience, even for a pest-control technician, the parasites have made a resurgence worldwide over the past twenty years.
Bed bug infestations, as well as giving discomfort to their victims from irritating bites, inflict costs on home and business owners for ongoing monitoring, treatment of infested rooms and furnishings, and potential disposal and replacement of infested items. Even back in 2005 bed bugs were reported as being common again in the urban environment in the US, Europe and Australia, infesting apartments, hotels, healthcare facilities and college dormitories (Romero, 2007).
A study of bed bugs in the US in 2007 found “extremely high levels of resistance” to common insecticides in multiple infestations across the country. It concluded that resistance was the “expected outcome of their repeated use”. Also, the failure of insecticides to quickly control infestations of resistant insect populations increased their opportunity to spread between rooms and buildings, and by recycling of furniture and bedding (Romero, 2007).
The increase in international air travel has also meant more people travelling to and from infested areas. This has provided bed bugs with more opportunities to spread — often in the luggage of travellers, as many an hotelier has found out.
Changes in the use of insecticides were also thought to have contributed to growing resistance in bed bugs. This includes the controlled application of insecticides, instead of widespread spraying, and the move away from organochlorines such as DDT. Pesticide resistance was, however, first noticed with the use of DDT in the 1950s.
Other studies have shown that insects can develop a range of adaptations that confer pesticide resistance. It is believed to be a result of exposure to treatments, including metabolic changes, increase in proteins and fats that bind to the pesticide chemical, and a thicker cuticle (insect ‘skin’) acting as a barrier to the pesticide entering the insect body. No previous research, however, had shown that pesticide-resistant bed bugs had a thicker cuticle.
What the research found
The researchers at the University of Sydney collected bed bugs from an infestation in a house and bred them in their lab to produce a group that were all the same age, had the same diet and conditions. They were placed on an insecticide-treated surface and removed as they were ‘knocked down’. They were separated into three groups that were knocked down within 2 hours (called intolerant), 4 hours (tolerant) and those that were unaffected after 24 hours (resistant).
The researchers then measured the cuticle thickness of the bed bugs by imaging cross sections of the bed bug legs using an electron microscope and drawing the boundaries of the cuticle on the image to measure the thickness (see figure 1).
They found that the length of time the bedbugs survived the insecticide treatment was related to the thickness of their cuticles. The cuticles of the most resistant group were on average 16% thicker than the intolerant group.
The researchers say that these results may help to explain why failures in the control of field investigations are so common. The results emphasise the need for an integrated pest management approach to the control of resistant bed bugs to prevent their spread.
They also conclude that the combination of adaptations to pesticides shown by bed bugs (the metabolic and physical changes) have important consequences for the formulation of insecticides in bed bug control.
Savvas Othon, Service and Science Innovation Director at Rentokil Initial, commented:
“There is no doubt that Bed Bugs have evolved thicker skins as detailed by the university and as we know, changes to morphology through evolution are triggered, in the main, by a need to survive and adapt to the environment. The wide use of chemicals could be such a trigger, however, this is hypothetical and will need further clarification, for example, mapping of historical bed bug samples to the level of insecticide use over time. Whether the evolution was triggered by insecticide use or not, the correlation between cuticle thickness and resistance is an important find and it may have implications on current treatment methods. For example, we could see the increased use in desiccant dusts to impact the insect cuticle as a compliment to insecticide treatments.”
Resistance is useless
Rentokil has developed a chemical-free method of pest control that is effective against removing bed bugs and other insects such as cockroaches, including those that have resistance to pesticides. Our Entotherm heat treatment won a Best Business Award for Best Innovation in the private sector. It uses a heat regime to kill insects — eggs, larvae and adults — and can be applied to a room or to items such as furniture placed inside a special pod. Treated areas can be re-used immediately after treatment with no residual side effects.
- Lilly, j. G. (2016, April 13). Cuticle Thickening in a Pyrethroid-Resistant Strain of the Common Bed Bug, Cimex lectularius L. (Hemiptera: Cimicidae). PlosOne.
- Romero, A. (2007). Insecticide resistance in the bed bug: a factor in the pest’s sudden resurgence? Journal of Medical Entomology, 44(2), 175-8.