Beware the thick skinned bed bugs (they’re beating our bug sprays)


Think you’re got thick skin? You may be able to brush off the odd insult but for bed bugs, their thick skin can ward off fatal doses of insecticides! This is just one way they’re beating our commonly used bug sprays.

The resurgence of bed bugs over the past couple of decades has been great fuel for media and pest control companies alike. From Paris to London and New York to Sydney, infestations in all forms of accommodation has made headlines.

Eradicating an infestation of bed bugs can be tricky, tricky and expensive. While control within the hospitality industry is improving, the impacts of bed bugs are now being felt in lower socioeconomic groups in the community. There are often financial barriers to effectively controlling infestations and controlling infestations is not getting any easier.

Working out why bed bugs are hard to kill

David Lilly is currently a postgraduate student in our lab undertaking his PhD with the University of Sydney. He has been doing some great work and its wonderful as a supervisor to see him starting to publish some of his research as he approaches the end of his candidature.

We’ve already published some research on bed bugs and insecticide resistance and the role of metabolic detoxification in driving this resistance (you can read about that work via at Entomology Today). However, some of the most exciting research has just been published and indicates that “thicker skinned” bed bugs are more resistant to pyrethroid insecticides.

It is one thing to demonstrate insecticide resistance in a pest but understanding why that resistance occurs is critical if we’re to develop more effective strategies to control bed bugs.

This project was inspired by a study that demonstrated that mosquitoes resistant to insecticides had thicker cuticle. Could the same phenomenon occur in bed bugs?

Working with the Australian Centre for Microscopy & Microanalysis at The University of Sydney, we were able to capture images of cross-sections of legs from resistant and susceptible strains of bed bugs. Measuring the cuticle thickness at various points and comparing those between the two strains of bed bugs allowed an assessment of changes in cuticle.

Those bed bugs resistant to insecticides had thicker cuticle. In fact, the cuticle of the resistant bed bugs was around 15% thicker. Thicker the cuticle, the tougher it is for insecticides to penetrate.

Given human’s propensity to use insecticides, it is little wonder our most loathsome pests, such as mosquitoes and bed bugs, are developing resistance. While there really aren’t many other options available to control bed bugs, insecticides will remain part of our pest control tool kit. Alternative strategies are always being considered but while insecticides remain, we need to be mindful of the development of resistance and ways we can slow (or overcome) that process.

Bed bug’s thick skins grab the media’s attention


The research has already received international media coverage thanks to the fantastic team at University of Sydney Media and Communications team. A quick “google news” search turns up over 70 news items reporting on the paper! You can catch up with coverage at Popular Science (Australia), Wired, USA Today, Daily Mail, Sydney Morning Herald, BBC, Newsweek, Gizmodo and Mirror.

The abstract for our paper is below:

Thickening of the integument as a mechanism of resistance to insecticides is a well recognised phenomenon in the insect world and, in recent times, has been found in insects exhibiting pyrethroid-resistance. Resistance to pyrethroid insecticides in the common bed bug, Cimex lectularius L., is widespread and has been frequently inferred as a reason for the pest’s resurgence. Overexpression of cuticle depositing proteins has been demonstrated in pyrethroid-resistant bed bugs although, to date, no morphological analysis of the cuticle has been undertaken in order to confirm a phenotypic link. This paper describes examination of the cuticle thickness of a highly pyrethroid-resistant field strain collected in Sydney, Australia, in response to time-to-knockdown upon forced exposure to a pyrethroid insecticide. Mean cuticle thickness was positively correlated to time-to-knockdown, with significant differences observed between bugs knocked-down at 2 hours, 4 hours, and those still unaffected at 24 hours. Further analysis also demonstrated that the 24 hours survivors possessed a statistically significantly thicker cuticle when compared to a pyrethroid-susceptible strain of C. lectularius. This study demonstrates that cuticle thickening is present within a pyrethroid-resistant strain of C. lectularius and that, even within a stable resistant strain, cuticle thickness will vary according to time-to-knockdown upon exposure to an insecticide. This response should thus be considered in future studies on the cuticle of insecticide-resistant bed bugs and, potentially, other insects.

The full citation is: Lilly DG, Latham SL, Webb CE, Doggett SL (2016) Cuticle Thickening in a Pyrethroid-Resistant Strain of the Common Bed Bug, Cimex lectularius L. (Hemiptera: Cimicidae). PLoS ONE 11(4): e0153302. doi:10.1371/journal.pone.0153302

Download the paper for free directly from PLoS ONE!

Oh, and if you’re worried about picking up bed bugs on your next holiday, here are some tips!


Entomology 2014: Portland, Oregon

Portland Oregon Retains Its "Weird" TitlePortland isn’t going to get any less “weird” when 3000 entomologists hit town! I’m going to be one of them there talking tweets and tweaking public health messages.

This month I’m heading along to the Entomology 2014: The Annual Meeting of the Entomological Society of America, 16-19 November in Portland, Oregon.

This will be the first time I’ve attended an ESA meeting and I’m really looking forward to it. These are large meetings with thousands of delegates, a big change from our recent Mosquito Control Association of Australia conference that attracted about 150 attendees! There is little doubt that I’ll be kept busy getting along to just a fraction of presentations I’m interested in. You can check the program yourself here.

A couple of interesting things I’m looking forward to (notwithstanding the coffee, record shopping and doughnuts) is the workshop on scientific writing, How not to write like a scientist, and a session on the role (or perhaps lack of a role) arthropods play in Ebola virus transmission. I’ve written about why mosquitoes don’t spread Ebola here.

I’ll be giving a couple of presentations, one on the role of mosquito repellents in managing mosquito-borne disease risk and another on the use of social media to promote public health messages. Both of these invited presentations are sure to be fun. It will be nice to catch up with some old friends during the repellent symposium. I recently contributed a book chapter to the new handbook on insect repellents edited by the session organizer/moderator Mustapha Debboun (alongside Dan Strickman and Steve Francis).  the symposium.The social media session will be fun too and, apart from sharing my experiences in using social media to promote public health messages, it will be great to catch up with many wonderful people who’ve made my experience on Twitter in recent years so rewarding.

My PhD student, David Lilly, will also be speaking on his work studying insecticide resistance in bed bugs. The abstracts for all these presentations are below but please note that due to the nature of some symposium, not abstracts are included on the Entomology 2014 online program.

Aedes aegypti

A researcher at Rockefeller University feeds her stock of yellow fever mosquitoes (Aedes aegypti). This approach remains one of the most effective ways to test new mosquito repellents. (Photo: Alex Wild)

1. Finding a place for mosquito repellents in mosquito-borne disease management: An Australian perspective

Webb CE

Mosquito-borne disease is a growing concern for local authorities in Australia. While broad scale mosquito control programs reduce nuisance-biting impacts in some instances, in most regions where mosquito-borne pathogens, particularly Ross River virus, pose a public health risk, local authorities rely on the promotion of personal protection measures. A key component of such strategies is the use of topical insect repellents. There is little evidence that confirms their effectiveness in preventing disease. However, many studies have indicated that the correct use of topical repellents can protect against biting mosquitoes. As a result, it is likely that the promotion of topical insect repellents will remain a critical component of personal protection measures. If they’re here to stay, health authorities must ensure the public is aware of how to effectively choose and use repellents. Currently, there is a disjointed approach to repellent advice provided by state and local authorities. What is needed is a national approach that sets the framework for

The Challenges and Significant Contributions of Insect Repellents to Vector Control

Sunday, November 16, 2014: 8:00 AM-12:00 PM
B115-116 (Oregon Convention Center)


The global resurgence in bed bugs has been attributed to increased international travel and a shift in household insecticide use but perhaps it is resistance that is driving the increasing pest impacts? (Photo: Steve Doggett)

The global resurgence in bed bugs has been attributed to increased international travel and a shift in household insecticide use but perhaps it is resistance that is driving the increasing pest impacts? (Photo: Steve Doggett)

2. The importance of methodology and strain selection when determining efficacy of insecticides against bed bugs

Lilly D, Webb CE and Doggett SL

Selection of an appropriate bioassay technique and insect strain(s) are known to be important factors when attempting to accurately detect and monitor for insecticide resistance or define the efficacy of an insecticide. Recent studies with both susceptible and resistant strains of the common bed bug, Cimex lectularius, have indicated these principles similarly apply to bed bugs and must be considered prior to undertaking diagnostic bioassays. Age, access to a blood meal, and the period since repletion may all influence the outcomes of bioassays with bed bugs. Dry residual deposits of insecticides, in particular those of neonicotinoids, also have the potential to overestimate resistance ratios or provide a false negative indication of efficacy when viewed in comparison to more applicable topical or wet residual exposure methods. Resistance monitoring of Australian field strains has also revealed that a wide spectrum in the magnitude of resistance can exist between strains that express identical resistance mechanisms, and that laboratory strains held in culture for long periods of time may lose resistance or change resistant genotypic frequencies. When factored in to the proliferation of field strains with various combinations of multiple and/or cross resistance mechanisms, this clearly presents a challenge to product manufacturers, registration bodies, and pest managers as to how they can ensure the experimental methodology and strain selected is most appropriate for the desired purpose or outcome. The results of laboratory investigations to provide informed guidance on recommended ‘best practise’ bioassays with bed bugs will be presented.

Graduate Student Ten-Minute Paper Competition: MUVE

Monday, November 17, 2014: 9:48 AM
B117-119 (Oregon Convention Center)


Engaging with the community is an important part of public health and beyond public meetings and workshops, social media may provided an effective way to get the messages out to increase awareness of mosquito-borne disease (Photo: Steve Doggett)

Engaging with the community is an important part of public health and beyond public meetings and workshops, social media may provided an effective way to get the messages out to increase awareness of mosquito-borne disease (Photo: Steve Doggett)

3. Can social media extend the reach of public health messages?

Webb CE

Increasing the exposure of public health messages is critical. This is particularly the case for mosquito-borne disease where advice on personal protection measures often informs the first line of defense against biting mosquitoes. Traditional media has been the mainstay of communication efforts by local authorities but could the use of social media provide a new vehicle for disseminating information and engaging with the wider community? The aims of this study were to determine if promotion and engagement via social media influenced how online information is accessed. A range of social media platforms, particularly Twitter, were employed to disseminate public health messages and engage the community and traditional media outlets. The total weekly exposure of “tweets” was measured for six months with approximately 40,000 people per week received tweets with maximum exposure of almost 190,000 people in a single week. Engagement with the accounts of traditional media (e.g. radio, print, television, online) was found to be the main route to increased exposure and, subsequently, to increased access of public health information online. With the increasing accessibility of the community to online resources via smartphones, researchers and public health advocates must develop strategies to effectively use social media. Many people now turn to social media as a source of news and information and those in the field of public health, as well as entomological research more generally, must take advantage of these new opportunities.

Wednesday, November 19, 2014: 8:00 AM-12:00 PM
Portland Ballroom 252 (Oregon Convention Center)

If you’re attending the meeting, please say hi if you’re passing by and feel free to introduce yourself using your twitter handle! If you’re not at the meeting, you can keep track by following the hashtag #EntSoc14. I’ll be trying to tweet about bits and pieces during the conference so please join the conversation!

The image at the top of this post taken from “Top ten things you didn’t know about Portland


Don’t let the “love bugs” bite this Valentine’s Day

What are you taking on your Valentines Day date? Flowers? Chocolates? Clean undies? Don’t forget to pack the insect repellents! There may be more than just “love bugs” about.

I’ve got you under my skin

The human scabies mite (Sarcoptes scabei) is the only arthropod to truly get under our skin. The tiny mite burrows in and feeds on dissolved human tissue in the tunnels they excavate. Itchy yet? Don’t start scratching as that is one way to release mites and infect your friends.  The other way is when mites come to the skin surface to mate. Newly “knocked up” females are usually quick to burrow into the skin but for those that don’t, they’re prime candidates for transfer.

Skin to skin contact is the typical way the mites are spread from person to person. A hand shake probably won’t do it but sexual contact will. Serious problems with scabies are also not uncommon in aged care facilities and can be a serious problem in Aboriginal communities. Even wombats can be infected.

Once infected, symptoms can take up to a month to develop. At that point, the infected person develops an allergic reaction to the mite’s faeces, skin moults, saliva or moulting fluids. The “mite tunnels” may appear as pale grey threadlike marks and often follow natural creases in the skin in areas such as the hands, particularly the webbing between the fingers, but also on the wrists, elbows, genitals and breasts. Large areas of the body can also be covered by a rash that is not specifically associated with the mite’s burrows but rather is thought to be a generalised allergic reaction. Severe itching all over the body can be experience with the intensity of irritation especially noticeable at night.

Typical scabies infestations are easily treated with an insecticide cream. Problem is, to confirm infection, you need to have a “skin scraping” taking to look for the mites, their eggs or faeces. Taking a “skin scraping” can be pretty nasty and the bulk of scabies infestations are diagnosed on symptoms alone. I think scabies infection is one of the most over diagnosed illness doing the rounds. From the calls I take (at least a couple a week), anyone who presents to their doctor or pharmacist with an itch appears to end up smearing a cream like this all over themselves. The problem is, when the cream doesn’t fix the itch (because the itch is caused by something other than mites), people may repeat the course of treatment once or twice more (as well as trying “other” solutions). That then leads to self inflicted skin irritation and the cycle continues. Correct diagnosis would avoid these problems!

Scabies infection can be even more serious in immunocompromised or elderly individuals when mite populations explode. Known as “crusted” or “Norwegian” scabies, the skin can take on a thicken appearance and contain huge numbers of mites. In these situations, the condition can be highly contagious and barrier nursing is required.


Intense activity of scabies mite in a case of “crusted” scabies (Photo: Stephen Doggett, Medical Entomology, Pathology West)

The “deadliest catch” on the dating scene or just “butterflies of love”?

Pubic lice, Pthirus pubis, (commonly known as crabs) have found a home on the pubic hair of humans (after apparently making the leap from gorillas around 3.3 million years ago). Different to head lice (Pediculus capitis), the claws of pubic lice are adapted to courser hair pubic region and lice and rarely (but occasionally) travel far from those regions. Unsurprisingly, they spread primarily through sexual contact. In many countries they’re classified as a sexually transmitted infection. However, they don’t really pose a significant health risk. They can cause severe itchiness in the infested regions but there are no known pathogens spread by their bites (interestingly though, there has been some suggestion that the presence of pubic lice may indicate the presence of more serious STIs).

You’ve probably seen the headlines. Prompted by this paper, there has been a lot of attention paid to the rise of the Brazilian waxing trend and the threat it poses to the natural habitat of pubic lice. Are the parasite’s days numbered? This probably isn’t the case. No, probably not.

Although there is some data on prevalence rates in Australia from the 1980s (about 1.5% of individuals visiting STI clinics), there really isn’t much more information available about just how widespread are pubic lice infestations (not much quantitative data on pubic hair trends amongst the general population is available either but there have been some attitudinal studies carried out in Australia). Cases of pubic lice is clearly rare but specimens do occasionally pop up in pathology samples submitted to our laboratory. I once tried to look into some data from local sexual health clinics but there just hasn’t been enough data collected to make any meaningful assessment on any changes in prevalence rates.

These days, with information more readily available online, individuals are probably more likely to buy treatments from chemists than attend sexual health clinics. Avenues to collect reliable data on prevalence rates may be difficult to find. Doesn’t seem to matter anyway as the “Brazillian” trend is apparently over. I can hear the tiny applause of crab claws the world over.

Life cycle of the pubic louse (taken from CDC)

Beware the sleepover stowaways

Bed bugs may not specifically be a sexually transmitted arthropod but nevertheless a parasite that may take advantage of some Valentine’s Day sleepovers. Bed bugs have been grabbing the headlines for the past 10-15 years as that make a stunning resurgence in many parts of the world. This resurgence has been attributed to, in some ways, by greater availability of cheap, fast international travel and resistance in bed bugs to commonly used insecticides (I currently have a PhD student investigating this).

Bed bugs don’t live on the body. They don’t just live in beds either. They live in almost any crack or crevice available that is also close to humans. Bedrooms obviously. Planning a special Valentine’s Day sleepover at the local hotel? Don’t be fooled into thinking bed bugs are only found in cheap accommodation, they’re just as likely to be lurking in five star hotels.

If bed bugs decide to make a meal of you, it isn’t just the bites that cause a problem. If they decide to hide away in your overnight bag, you may find yourself dealing with an expensive and inconvenient pest control operation in your home. Best avoid them in the first place.

Best check for any stowaways in Valentine’s Day gifts too.

bedbug_stevedoggettNot the souvenir you were hoping for?

Is your partner rushing home from overseas for Valentine’s Day? Make sure they don’t bring home a less than special gift of mosquitoes or mosquito-borne disease!

As highly unusual as it sounds, transporting infected mosquitoes in luggage has been the cause of infections in non-endemic regions. There have been documented cases of “baggage malaria“. Even in Australia, we’ve had a suspected case of “baggage dengue” in Western Australia. While “airport” malaria and dengue cases have been reported in many regions, perhaps the same rapid international travel that appears to be driving the resurgence in bed bugs may increase the risk of baggage-assisted movement of infected mosquitoes?

Even if your partner manages to avoid bringing home any infected mosquitoes, perhaps a passionate reunion could lead to a highly unusual case of sexually transmitted infection. A scientist working in Senegal returned home to Colorado only to infect his wife with the (normally only) mosquito-borne Zika virus (a virus closely related to Japanese encephalitis virus and West Nile virus rarely recorded outside Africa). Interestingly, we’re currently seeing an outbreak of Zika virus in the Pacific so best be warned if your partner has just returned from French Polynesia!

So, does this mean mosquito-borne viruses like Zika, West Nile, dengue or Ross River could be sexually transmitted human-to-human? We know viruses are sexually transmitted between mosquitoes but apart from the case of Zika virus infection discussed here, I’m not aware of any other reported cases in humans. Strange given the huge numbers of cases that occur during dengue outbreaks. Perhaps nobody has thought to check? The semen of boars has been checked and they found Japanese encephalitis virus….

Wild pig (Sus scrofa) (Photo National Aeronautics and Space Administration)

Who would have thought there were so many entomological risks associated with Valentine’s Day?

To find out more about arthropods of public health concern in Australia, check out this document I put together for the Australian Federal Government Department of Health and Aging. It is available for free download as either PDF or WORD versions.

Webb CE, Doggett SL and Russell RC. (2013). Arthropod pests of public health significance in Australia. Department of Health and Aging, Canberra. ISBN: 9781742419770. [PDF]

(Photo of the Alaskan King Red Crab at the top of this post is taken from Wikipedia.)

Australian Entomological Society conference 2013


Common bed bug (Photo: Stephen Doggett, Medical Entomology, Pathology West – ICPMR Westmead)

The annual conference of the Australian Entomological Society is on next week. Although I’ll be missing the trip to Adelaide this year, our lab will be represented with some presentations on bed bugs and biting insects!

The 44st AGM and Scientific Conference of the Australian Entomological Society will be held from 29 September through until 2 October 2013 in Adelaide, South Australia. These meetings are great and I’m disappointed not to be attending this year. The meetings attract a wide range of researchers in the field of entomology, from those working on agricultural pests through to ecologists using arthropods to measure environmental change.

The theme of the conference is “Invertebrates in extreme environments”. I was originally planning on presenting some work on the saltmarsh mosquito, Aedes vigilax. This is an insect that thrives in the super saline conditions of tidally influenced saltmarsh habitats. It has adapted to these environments be developing dessication resistant eggs, the ability to lay its first batch of eggs without the need for a blood meal and can disperse many kilometers from the wetlands. It also happens to be a major nuisance-biting pest and vector of pathogens including Ross River virus. Time and budgets squished that plan unfortunately, perhaps next time.

I will be there in spirit though as co-author on a couple of presentations:

A New Resource on Medical Entomology

Webb, C.E., Doggett S.L. & Russell R.C.

The field of medical entomology covers much more than just mosquitoes! A new resource will soon be available to those government and non-government organisations that often need to provide advice on a range of arthropods of medical importance in Australia. The Environmental Health Committee (enHealth) of the Australian Government Department of Health and Ageing has commissioned the production of revised guides for the management of arthropod pests of public health importance in Australia. The original document, Guidelines for the Control of Public Health Pests: Lice, fleas, scabies, bird mites, bedbugs and ticks, was produced in 1999 and, while providing a useful resource for environmental health officers responding to enquiries from the general public, much of the information had become outdated. There was also a number important pests and/or pest groups left out of the original document. A new version of the document is expected to be made available for public comment in 2013 and this presentation will summarise some of the key features of, and additions to, the revised document.


Insecticide Resistance In Bed Bugs In Australia: Are They Getting A Little Too Cozy In Your Bed?

Lilly, D.G., M.P. Zalucki, S.L. Doggett, C.J. Orton, R.C. Russell & C.E. Webb

Insecticide resistance in bed bugs has been nominated as a major factor in the pest’s resurgence. Recent studies using field and laboratory strains of Cimex lectularius and C.hemipterus across Europe, Africa, Asia and North America have variously demonstrated resistance to the pyrethroids, carbamates and, to a lesser extent, the organophosphates. Resistance has been suspected in Australia, with anecdotal reports of treatment failures due to poor product performance. Early efficacy investigations on a range of formulated products found indications of resistance in an Australian derived strain of C. lectularius. To confirm if resistance was present, four compounds (permethrin, deltamethrin, bendiocarb and pirimiphos-methyl) encompassing the major groups of insecticides then registered for bed bug control in Australia were selected for bioassay along with one compound (imidacloprid) to which strains should not have received any exposure at that time. LD50 values (at 24 h) were determined via topical application of the technical grade compounds serially diluted in acetone against a suspected resistant strain (collected from and designated the ‘Sydney’ strain) and a susceptible laboratory strain imported from Bayer CropScience AG, Germany (the ‘Monheim’ strain). All tests were conducted using mixedsex adult bed bugs that had been offered a blood meal within the last 7 days. All compounds tested against the Monheim strain demonstrated high levels of insecticidal activity. However, for the Sydney strain only pirimiphos-methyl and imidacloprid showed high levels of efficacy. Bendiocarb, permethrin and deltamethrin all failed to return greater than 60% mortality at the maximum applied rate of 100μg/μL. The resistance factor (calculated as: Sydney LD50 / Monheim LD50) for each compound was:permethrin = 1.4 million, deltamethrin = 430,000, bendiocarb = 240, pirimiphos-methyl =2.8, imidacloprid = 2.7. Thus using this experimental protocol, resistance was detected with the pyrethroids and carbamates, but not the organophosphates or neonicotinoids (with thedifferences reflected against those compounds likely due instead to a minor resistance- related fitness cost or physiological difference between the strains). This research has significant implications for current and future insecticide management when attempting to control bed bugs. Further studies are ongoing to determine the mechanism(s) of resistance.

It looks like it will be a great meeting with lots of interesting presentations. The full program is available here and I hope there’ll be some tweeting using the hastag #AES2013

Conversations in 2012

It was one of my great pleasures in 2012 to be asked to write some articles for the wonderful website The Conversation. The Conversation is an independent source of analysis, commentary and news from the university and research sector — written by acknowledged experts and delivered directly to the public.

The writing style at The Conversation is vastly different to writing for peer-reviewed scientific journals and I strongly feel as though my writing has greatly improved for the experience. As well as a steady increase in confidence writing in a “The Conversation” style, putting together a few articles on the year has also helped improve the way I write other material (e.g. fact sheets, articles for trade bulletins, newsletters etc). I’ve even found it has helped in the way I put together lectures and conference presentations too.

Here are the pieces I wrote for The Conversation in 2012:

Time to regulate the release of GM mosquitoes – and here’s how (February 2012)

Taking the ouch and itch out of insect bites (April 2012)

Will bugs bite at the London Olympics? (July 2012)

Bed bugs at the London Olympics [Video presentation in conjunctions with SBS World News] (July 2012)

Explainer: West Nile virus outbreak in the United States (August 2012)

Using urban planning to reduce mosquito-borne disease (November 2012)

Monday’s medical myth: mosquitoes prefer sweet blood (December 2012)

My articles have had over 14,000 readers and I hope I’ve been able to pass on some useful public health advice on avoiding biting arthropods and the pathogens they may (potentially) transmit!

I must also pass on my many thanks for the assistance and encouragement provided by the two editors responsible for wrangling my writing, Reema Rattan and Fronscesca Jackson-Webb.