A heavyweight study involving a team of international researchers has definitively answered the question, ‘Do mattress protectors really work against bed bugs?’
The tropical bed bug, Cimex hemipterus and common bed bug, Cimex lectularius present a global problem. Their presence is widespread and they are difficult to treat as levels of insecticide resistance are growing. In fact, in studies assessing resistance, all the field collected strains of the common and tropical bed bug have been found to be resistant to pyrethroids, with resistance further being reported to other types of insecticides, including neonicotinoids, organochlorides and organophosphates.
The pest control market has responded by developing products that attempt to tackle the problem by creating a physical as well as a chemical barrier. In the US, consumers can purchase mattress protectors and liners that are made from fabric impregnated with a pyrethroid. One example is the ActiveGuard mattress liner, a US product that contains 1.64% permethrin and was developed to protected against dust mites. Today it is being marketed for bed bug control. But the question is: does it really work?
Pyrethroid-impregnated mattress liners
A study published in Journal of Economic Entomology in May 2022 tested the efficacy of the permethrin-impregnated mattress liner against the tropical and common bed bug in laboratories around the globe, in one coordinated study. In an effort spanning several years, the team of international researchers including Dr Chow-Yang Lee from the University of California and David Lilly and Stephen Doggett from the University of Sydney, Westmead Hospital, tested the ActiveGuard mattress liner against 24 strains of bed bugs.
The purpose of the study was to determine if pyrethroid-impregnated mattress liners should, or should not be, recommended as part of an overall bed bug management program. The strains included both C. lectularius and C. hemipterus species originating from Australia, Malaysia, Sweden, the UK, and the US, with 21 collected during the modern resurgence of pyrethroid resistance.
In their natural environment, bed bugs move around frequently when looking for a host or harbourage. With this in mind, the researchers created three experimental conditions to test how effective the permethrinimpregnated mattress liner proved against bed bugs.
The first experiment evaluated the efficacy of the mattress liner when bed bugs were held on it continuously, in a long-term exposure. The second experiment examined the effectiveness of short-term exposure, when the bed bugs moved around and were in contact with the liner intermittently, for either four hours or six hours in total. The third experiment tested the liner in a way that reflects its real-world use, in what was called the ‘double fabric’ experiment. Here, the mattress liner was covered with non-treated 100% polyester fabric (to replicate a bed sheet), with the bed bugs held continuously on top.
In each of the three experiments, the researchers recorded the number of bed bugs that were knocked down after increasing periods of time. As well as the pyrethroid-resistant strains, pyrethroid-susceptible bed bugs were also tested as a control.
In the long-term exposure trial, when bed bugs were held continuously on the mattress liner, 100% mortality was achieved within 24 hours in the control study of the US bed bugs with pyrethroid susceptibility. The resistant bed bugs were different; after 24 days of constant contact with the mattress liner, knockdown and mortality for the three other US strains was recorded as 84%, 32%, and 52%.
The Australian strains proved much more hardy; even after seven days of continuous exposure to the mattress liner, not all the bed bugs were knocked down or killed. For most Australian strains, mortality was less than 10%. No bed bugs of the Sydenham or Melbourne strains were knocked down or killed at all.
Pyrethroid resistance in Australian bed bugs
So just how resistant to pyrethroids are the different strains of bed bugs that we encounter in Australia? The Australian field strains used in this study exhibited a range of resistance levels when exposed to a dose of deltamethrin. The Adelaide and Ripponlea strains had low-level resistance, while the Parramatta, Tamworth, Sydenham, and Newcastle strains demonstrated mid-level resistance. Topping the table, the Alice Springs and Melbourne strains showed the highest resistance levels (Lilly et al. 2018).
In the short-term exposure, where the bed bugs were exposed to the mattress liner for four or six hours intermittently, the knockdown rate varied greatly for the US bed bugs. One US strain was knocked down within six hours of exposure to the liner, achieving 100% mortality, while another strain displayed only 2% mortality. This is similar to the Australian Parramatta strain, which is highly resistant, with only 4% mortality being recorded.
The ‘double fabric’ experiment was perhaps the most interesting as it reflects real-life use of commercially available mattress liners. When the pyrethroid-susceptible bed bugs were placed on the surface as a control test, 58-82% mortality was recorded for the UK and Australian bed bugs respectively. This shows that, when used against non-resistant strains, the mattress liner proved somewhat effective.
When tested against resistant Malaysian strains, 0-16% mortality was recorded after 96 hours of exposure. As only a 46% mortality rate was achieved with the least resistant Australian strain (Ripponlea), the double fabric study was not conducted using the other resistant Australian bed bug strains, as it was highly unlikely that any significant mortality would be recorded.
In conclusion, the mattress liner failed to achieve adequate levels of mortality against most of the strains of C. lectularius and C. hemipterus used in this study. In fact, for many strains, in spite of being in constant contact with the liner for seven days or more, little mortality was observed.
The efficacy of the liner was reduced even further when it was covered with a piece of fabric, as is the recommended use for the product. The product description instructs that a ‘mattress pad, barrier encasement or bottom sheet [is fitted] over the mattress liner’ so that the impregnated liner is not in direct contact with human skin (ActiveGuard, 2012).
The only Australian strain whereby a moderate degree of knockdown or mortality was achieved using the mattress liner was the Ripponlea strain, which is one of the least resistant bed bug strains. So what does this mean for pest managers? Is there any instance where pyrethroid-impregnated mattress liners should be recommended as part of an IPM approach to bed bug control?
According to the researchers, no. “The use of a permethrin-impregnated mattress liner over the short or long term is likely to select for the more pyrethroid-resistant bed bug individuals within a population and drive pyrethroid resistance levels even higher. Ultimately, this will make bed bug control more challenging, and may also lead to cross-resistance with other chemical classes, as has recently been reported,” states the report.
In light of the poor performance results, and the fact that pyrethroid resistance is so widespread globally, the evidence suggests that permethrin-impregnated mattress liners should not be recommended as part of an overall bed bug management program involving either C. hemipterus or C. lectularius.
What about standard mattress protectors?
Although pyrethroid-impregnated mattress protectors should not be used in bed bug management, standard mattress protectors are still an option to include as part of an integrated pest management plan, as detailed in the ‘Industry Code of Pest Practice for Bed Bug Management’ (S. Doggett), which was updated in 2022.
Suitable mattress protectors can be used in two ways. Firstly, they can be used for containment – the mattress protector is applied to a mattress already infested with bed bugs. This avoids the need to throw out the mattress or treat it with insecticide. However, as bed bugs can live for over six months, the mattress cover needs to be kept in place for close to a year to ensure all bed bugs are dead. Secondly, they can be used to prevent the mattress becoming a bed bug hiding place. As bed bugs love to hide in mattress seams, the protector eliminates these favoured hiding spots. Such mattress protectors can easily be removed for cleaning.
Suitable mattress protectors for bed bug management must be ‘seamless’, with small zipper teeth and a zipper stop to prevent bed bugs escaping. They also require an in-built bite-proof membrane to prevent any bed bugs trapped within the protector biting through to a human sleeping on top.
Further reading: Leong, Xin-Yeng & Lee, Chow-Yang & Singham, Veera & Chong, Alexander & Naylor, Richard & Naylor, Alexia & Miller, Dini & Wilson, Morgan & Lilly, David & Doggett, Stephen. (2022). The Efficacy of a Pyrethroid-impregnated Mattress Liner on Multiple International Strains of Cimex lectularius (Hemiptera: Cimicidae) and Cimex hemipterus (Hemiptera: Cimicidae). Journal of Economic Entomology. 10.1093/jee/toac067.