Bed bugs shape the indoor microbial community composition of infested homes

Invasive indoor pests under the microbiological lens: Bacterial and viral diversity from local to global scales in bed bugs and cockroaches

Essentially all animal life interacts closely with an array of microorganisms such as bacteria and viruses, which can have both beneficial and harmful effects. The advancement of high-throughput molecular biology approaches (DNA and RNA sequencing) has led to an ongoing boom in investigating the composition and functions of microbial communities (microbiota) associated with a wide range of animal taxa, including insects. As this area of investigation has blossomed, such research on indoor urban insect pests has lagged more widely studied species. However, over the last several years, significant strides have been made in understanding the diversity and biological roles of microbes associated with such insects. This review highlights and discusses recent key findings, focusing on bed bugs and cockroaches, two of the most prolific globally invasive indoor insect pests. Advances in this area of research have long-term implications for public health and for the development of novel pest control approaches.

Effects of surface type and distance traveled on the efficacy of a Beauveria bassiana (Hypocreales:Cordycipitaceae)-based biopesticide (Aprehend) for bed bug (Hemiptera: Cimicidae) control

The cryptic behavior that characterizes bed bugs (Cimex lectularius L.) makes them one of the most difficult indoor pests to control. Thus, the use of products with long residual efficacy is a key component of successful bed bug management. Aprehend is a biopesticide for bed bug control, whose active ingredient is the entomopathogenic fungus, Beauveria bassiana. This product shows promise for extended bed bug control against pyrethroid-resistant bed bugs, causing mortality days after contact with the treated surface. However, it is unclear how surface type and distance traveled by bed bugs over a treated surface impact efficacy. Therefore, we evaluated the efficacy of different Aprehend band widths applied to different substrates commonly encountered by bed bugs, looking specifically at average time to mortality and overall mortality. Our findings indicate that exposure to fresh applications of Aprehend resulted in high mortality when bed bugs traveled very short distances (1 cm) over some Aprehend-treated surfaces (vinyl tile and cotton jersey fabric), while exposure to other treated surfaces (unfinished pinewood and painted drywall) resulted in comparatively lower mortality even over longer distances (5 cm). Furthermore, we found that bed bugs crawling on cotton jersey fabric picked up a significantly higher number of spores compared to unfinished pinewood. These results indicate that applications of Aprehend as 5 cm (2 inches) bands according to label recommendations can be effective, although surface type is an important determinator of efficacy. This information will help guide pest management professionals in their use of B. bassiana for bed bug control.

Efficacy of steam and diatomaceous earth dust against the tropical bed bug Cimex hemipterus (F.) under laboratory and field conditions

BACKGROUND

Over the past two decades, bed bugs (Cimex spp.) have resurged as common urban pests around the world. The search for efficient and safe control measures has become a key interest among researchers, manufacturers, and pest control professionals. In this study, we evaluated and compared the efficacy of steam, diatomaceous earth (DE) dust, and a combination of both against tropical bed bugs (Cimex hemipterus (F.)) under laboratory and field conditions.

RESULTS

In the laboratory study, the mortality of bed bugs after 2 days of exposure to DE dust was 100%. When bed bugs stayed on the surface of an object or in cracks, a brief steam treatment (1 s) caused 100% mortality. However, when bed bugs were hidden under a fabric cover, steam application for 10 s only caused 89 ± 6% mortality. Bed bugs that survived steam treatment exhibited reduced feeding activity. In a 14-week long study, there was no significant difference in the reduction rate of bed bugs between steam treatment and DE dust treatment. A 37-week long control study showed that steam and steam plus DE dust treatments eliminated 97-100% of the infestations.

CONCLUSION

Applying steam and DE dust are effective strategies for eliminating natural tropical bed bug infestations. Continuous follow-up monitoring and treatment until no bed bugs are found are crucial in completely eliminating the infestation of tropical bed bugs. © 2024 Society of Chemical Industry.

Semiochemicals modulating bed bug behaviour

The common bed bug, Cimex lectularius (Cimicidae, Hemiptera), is obligate haematophagous and can carry pathogens but is not known to transmit diseases to humans in natural settings. Bed bugs are activated and guided by semiochemicals and heat by potential hosts, as well as by an aggregation pheromone when searching for food and home. No sexual pheromone has been detected in bed bugs, which mate through traumatic insemination. First, after mounting, males are able to distinguish between large nymphs, other males, and females. To avoid unwanted traumatic inseminations, nymphs and adults emit an alarm pheromone. The olfactory system of bed bugs has relatively few odorant and ionotropic receptors, which likely reflects the simple environment that bed bugs live in, and use to search for hosts and conspecifics.

Deciphering the distribution of microbial communities and potential pathogens in the household dust

The reliance of modern society on indoor environments increasing has made them crucial sites for human exposure to microbes. Extensive research has identified ecological drivers that influence indoor microbial assemblages. However, few studies have examined the dispersion of microbes in different locations of identical indoor environments. In this study, we employed PacBio Sequel full-length amplicon sequencing to examine the distribution of microbes at distinct locations in a single home and to identify the potential pathogens and microbial functions. Microbial communities differed considerably among the indoor sampling sites (P < 0.05). In addition, bacterial diversity was influenced by human activities and contact with the external environment at different sites, whereas fungal diversity did not significantly differ among the sites. Potential pathogens, including bacteria and fungi, were significantly enriched on the door handle (P < 0.05), suggesting that door handles may be hotpots for potential pathogens in the household. A high proportion of fungal allergens (34.37 %-56.50 %), which can cause skin diseases and asthma, were observed. Co-occurrence network analysis revealed the essential ecological role of microbial interactions in the development of a healthy immune system. Overall, we revealed the differences in microbial communities at different sampling sites within a single indoor environment, highlighting the distribution of potential pathogens and ecological functions of microbes, and providing a new perspective and information for assessing indoor health from a microbiological viewpoint.

Volatile Organic Compounds: A Promising Tool for Bed Bug Detection

The recent decades' resurgence of bed bugs as a public health concern in industrialized countries has driven an increased interest on new sustainable insecticide-free methods to monitor and control these ectoparasites. Current methods of detection rely mainly on visual inspection or canine scent detection, which are methods that are time-consuming, require experience, are non-specific or require costly mission repetitions. Volatile organic compounds (VOCs) are considered an environmentally friendly alternative and a promising approach for bed bug detection. An overview of the released literature on VOCs, their chemical characteristics and their role in bed bugs' intra- and inter-species communications allowed us to highlight the identification of 49 VOCs in Cimex lectularius (23 molecules) and C. hemipterus (26), which are emitted by both sexes during diverse compartments including aggregation (46), mating (11), defense (4), etc., and all life stages including exuviae or dead bed bugs as a principal indicator of infestation. The latter has a great importance for application of these semiochemicals in successful detection and control management of bed bugs and to prevent their further dispersion. This approach has the advantage of more reliability compared to conventional detection methods with no need for repeated inspections, household furniture moving or resident rehousing for bed bugs' VOC detection, which are commonly performed by active or passive sampling with absorbing tubes and analyzed by gas chromatography-based analytical platforms.

Histamine Excretion by the Common Bed Bug (Hemiptera: Cimicidae)

The common bed bug (Cimex lectularius L.) is a hematophagous pest species that lives in close proximity to humans. Following a blood meal, bed bugs deposit fecal material indoors. The feces contain a variety of compounds, including histamine, which serves as a component of their aggregation pheromone. Histamine is a pivotal mammalian immune modulator, and recently it was shown to be present in high concentrations in household dust from homes infested with bed bugs. To better understand the dynamics of histamine excretion, we analyzed bed bug fecal material from different life stages and populations, along with fecal material collected at different post-feeding times and from bed bugs fed on different diets. Our analysis showed significant variation in histamine excretion among life stages, with mated females excreting the most histamine and first instar nymphs excreting the least histamine. However, when histamine excretion was normalized for blood consumption, males were found to excrete more histamine than the other life stages. There was no difference in histamine excretion among laboratory and recently home-collected bed bug populations. Further, we found histamine excretion continued for at least 14 d post-feeding, with the highest amount of histamine excreted 3-4 d after a bloodmeal. Overall, this work demonstrates that bed bugs excrete histamine across all feeding life stages, populations, and at various times after feeding, and that histamine excretion is directly related to blood feeding. These results will be used to better understand the health risks associated with histamine excretion and potential mitigation strategies of environmental histamine.

Quantification of Fecal Spot Production as a Measure of Environmental Contamination Based on Common Bed Bug (Hemiptera: Cimicidae: Cimex lectularius L.) Population Size

The presence of fecal spots has often been used to verify the existence of a bed bug (Cimex lectularius) infestation. However, no research has been conducted to determine how much fecal material that a bed bug population produces over time. In this study, the number of fecal spots that each nymphal life stage was capable of producing after a bloodmeal was quantified. Adult fecal spots were also quantified to determine if there was consistent production between feedings. During this study, it was discovered that bed bugs produced visible fecal spots and clear spots that were only visible under ultraviolet light. Therefore, three types of fecal spots were quantified: dark feces, light feces, and clear spots. Clear spots were produced in greater amounts (38.5-55.5%) than either dark spots (27.3-40.7%) or light spots (17.3-21.9%). For example, 5th instar bed bugs were thought to produce an average of 21 spots (dark and light) after a single bloodmeal. However, using the ultraviolet light, it was found that the 5th instars actually produced an average of 44.7 spots. Using the total fecal spot data collected during this study, researchers could project contamination potential for an infestation starting with a single gravid female over 30, 60, and 90 d. In addition, the amount of area covered by these spots was projected to be over 12 m2 in just 3 mo, which could greatly reduce the environmental and aesthetic quality of a home.

Comparative Efficacy of a Fungal Entomopathogen with a Broad Host Range against Two Human-Associated Pests

The ability of a fungal entomopathogen to infect an insect depends on a variety of factors, including strain, host, and environmental conditions. Similarly, an insect’s ability to prevent fungal infection is dependent on its biology, environment, and evolutionary history. Synanthropic pests have adapted to thrive in the indoor environment, yet they arose from divergent evolutionary lineages and occupy different feeding guilds. The hematophagous bed bug (Cimex lectularius) and omnivorous German cockroach (Blattella germanica) are highly successful indoors, but have evolved different physiological and behavioral adaptations to cope with the human-built environment, some of which also reduce the efficacy of fungal biopesticides. In order to gain greater insight into the host barriers that prevent or constrain fungal infection in bed bugs and German cockroaches, we tested different doses of Beauveria bassiana GHA through surface contact, topical application, feeding, and injection. Bed bugs were generally more susceptible to infection by B. bassiana with the mode of delivery having a significant impact on infectivity. The German cockroach was highly resilient to infection, requiring high doses of fungal conidia (>8.8 × 104) delivered by injection into the hemocoel to cause mortality. Mortality occurred much faster in both insect species after exposure to surfaces dusted with dry conidia than surfaces treated with conidia suspended in water or oil. These findings highlight the importance of developing innovative delivery techniques to enhance fungal entomopathogens against bed bugs and cockroaches.

Procurement Competence and Framework Agreements for Upgraded Bed Bug Control [Cimex lectularius (Hemiptera: Cimicidae)]

The prevalence of bed bugs (Cimex lectularius L.) is increasing worldwide. Due to this increase, low-income housing owners and managers need an efficient method for controlling the pests without excessive resource use. The quality of pest control efforts is crucial for efficient eradication. Infestations often need to be approached using a variety of strategies through an integrated pest management (IPM) framework. Efficient eradication is often thought to be the responsibility of the pest control contractor alone. However, the purchase and supply management theory suggests that optimal solutions actually involve sound buyer-supplier relations to support the strategic aim of pest eradication. This study illustrates the positive outcomes of elevating pest management competence on the buyer's part. Further, this study outlines a large-scale purchase situation that quantifies bed bug control efforts, in addition to their outcomes. In total, 11,000 apartment units were observed in Oslo, Norway, over a period of six years. The release and implementation of a procurement officer together with a state-of-the-art pest management framework agreement quickly reversed the consistent escalation of bed bug infestations in the observed units. Observations revealed that the study yielded the most success in eradicating bed bugs by increasing both the number of visits to the infested apartment and the overall duration of control efforts. The improved control was achieved at a reduced cost per infested apartment unit, which allowed for the implementation of bed bug preventive measures and building-wide inspections. The observations made in this study have been discussed in the context of the impact of bed bugs in low-income communities, relative to the factors of pest burden, demography, socioeconomics, and the welfare system in Norway.

A Francisella tularensis-Like Bacterium in Tropical Bed Bugs from Madagascar

The genus Francisella includes several highly virulent human pathogens and some tick endosymbionts. Francisella infections are acquired by humans through contact with vertebrate animal reservoirs or contaminated water or dust. The species Francisella tularensis can also be transmitted by arthropods including ticks, mosquitoes, and flies. For the first time, we describe the molecular detection of an F. tularensis-like bacterium in bed bugs from samples collected in rural Madagascar. This finding suggests a potential involvement of bed bugs in the ecology of Francisella. The role of bed bugs as possible hosts, reservoirs, or vectors of Francisella spp. should be further investigated.

Human skin triglycerides prevent bed bug (Cimex lectularius L.) arrestment

Bed bugs (Cimex lectularius) have proliferated globally and have become one of the most challenging pests to control indoors. They are nocturnal and use multiple sensory cues to detect and orient towards their human hosts. After feeding, usually on a sleeping human, they return to a shelter on or around the sleeping surface, but not directly on the host. We hypothesized that although human skin odors attract hungry bed bugs, human skin compounds may also prevent arrestment on hosts. We used arrestment assays to test human skin swabs, extracts from human skin swabs, and pure compounds identified from human skin swabs. When given a choice, bed bugs preferred to arrest on substrates not previously conditioned by humans. These responses were consistent among laboratory-reared and apartment-collected bed bugs. The compounds responsible for this behavior were found to be extractable in hexane, and bed bugs responded to such extracts in a dose-dependent manner. Bioassay-guided fractionation paired with thin-layer chromatography, GC-MS, and LC-MS analyses suggested that triglycerides (TAGs), common compounds found on human skin, were preventing arrestment on shelters. Bed bugs universally avoided sheltering in TAG-treated shelters, which was independent of the number of carbons or the number of double bonds in the TAG. These results provide strong evidence that the complex of human skin compounds serve as multifunctional semiochemicals for bed bugs, with some odorants attracting host-seeking stages, and others (TAGs and possibly other compounds) preventing bed bug arrestment. Host chemistry, environmental conditions and the physiological state of bed bugs likely influence the dual nature behavioral responses of bed bugs to human skin compounds.

Classroom microbiome, functional pathways and sick-building syndrome (SBS) in urban and rural schools - Potential roles of indoor microbial amino acids and vitamin metabolites

Sick building symptoms (SBS) are defined as non-specific symptoms related to indoor exposures, including mucosal symptoms in eye, nose, throat, and skin, and general symptoms as headache and tiredness. Indoor microbial composition is associated with SBS symptoms, but the impact of microbial functional genes and potential metabolic products has not been characterized. We conducted a shotgun microbial metagenomic sequencing for vacuum dust collected in urban and rural schools in Shanxi province, China. SBS symptoms in students were surveyed, and microbial taxa and functional pathways related to the symptoms were identified using a multi-level linear regression model. SBS symptoms were common in students, and the prevalence of ocular and throat symptoms, headache, and tiredness was higher in urban than in rural areas (p < 0.05). A significant higher microbial α-diversity was found in rural areas than in urban areas (Chao1, p = 0.001; ACE, p = 0.002). Also, significant variation in microbial taxonomic and functional composition (β-diversity) was observed between urban and rural areas (p < 0.005). Five potential risk Actinobacteria species were associated with SBS symptoms (p < 0.01); students in the classrooms with a higher abundance of an unclassified Geodermatophilaceae, Geodermatophilus, Fridmanniella luteola, Microlunatus phosphovorus and Mycetocola reported more nasal and throat symptoms and tiredness. Students with a higher abundance of an unclassified flavobacteriaceae reported fewer throat symptoms and tiredness. The abundance of microbial metabolic pathways related to the synthesis of B vitamins (biotin and folate), gamma-aminobutyric acid (GABA), short-chain fatty acids (SCFAs), and peptidoglycan and were protectively (negatively) associated with SBS symptoms (FDR < 0.05). The result is consistent with human microbiota studies, which reported that these microbial products are extensively involved in immunological processes and anti-inflammatory effects. This is the first study to report the functional potential of the indoor microbiome and the occurrence of SBS, providing new insights into the potential etiologic mechanisms in chronic inflammatory diseases.

Experimental infection of bed bugs (Cimex lectularius L.) with Burkholderia multivorans

The bacterium Burkholderia multivorans is an opportunistic nosocomial pathogen of humans. A previous study reported molecular detection of this bacterium in several specimens of the common bed bug (Cimex lectularius L.) collected from an elderly care facility in the U.S.A., raising questions about the possibility of vector-borne transmission. However, the ability of B. multivorans to colonize bed bugs and the ability of bed bugs to transmit the bacteria both remained untested. To resolve this knowledge gap, here we performed a set of experiments to examine the persistence and shedding of B. multivorans following ingestion by bed bugs in a blood meal. We isolated viable B. multivorans from the bodies of bed bugs for up to 13 days post-ingestion, but bacterial load substantially diminished over time. By 16 days post-ingestion, the bacteria could not be isolated. Further, B. multivorans was not shed in the saliva of infected bugs during feeding nor was it transmitted vertically from infected insects to their progeny. Based on these results, significant biological or mechanical transmission of B. multivorans to humans by bed bugs appears unlikely. Nonetheless, some viable bacteria were passively shed into the environment through defecation, a process which could potentially contribute to transmission through indirect contamination under rare circumstances.

Resistance to Fipronil in the Common Bed Bug (Hemiptera: Cimicidae)

Cimex lectularius L. populations have been documented worldwide to be resistant to pyrethroids and neonicotinoids, insecticides that have been widely used to control bed bugs. There is an urgent need to discover new active ingredients with different modes of action to control bed bug populations. Fipronil, a phenylpyrazole that targets the GABA receptor, has been shown to be highly effective on bed bugs. However, because fipronil shares the same target site with dieldrin, we investigated the potential of fipronil resistance in bed bugs. Resistance ratios in eight North American populations and one European population ranged from 1.4- to >985-fold, with highly resistant populations on both continents. We evaluated metabolic resistance mechanisms mediated by cytochrome P450s, esterases, carboxylesterases, and glutathione S-transferases using synergists and a combination of synergists. All four detoxification enzyme classes play significant but variable roles in bed bug resistance to fipronil. Suppression of P450s and esterases with synergists eliminated resistance to fipronil in highly resistant bed bugs. Target-site insensitivity was evaluated by sequencing a fragment of the Rdl gene to detect the A302S mutation, known to confer resistance to dieldrin and fipronil in other species. All nine populations were homozygous for the wild-type genotype (susceptible phenotype). Highly resistant populations were also highly resistant to deltamethrin, suggesting that metabolic enzymes that are responsible for pyrethroid detoxification might also metabolize fipronil. It is imperative to understand the origins of fipronil resistance in the development or adoption of new active ingredients and implementation of integrated pest management programs.

Molecular analysis of the blood meals and bacterial communities of bed bugs (Cimex lectularius L.) to assess interactions with alternative hosts

Common bed bugs (Cimex lectularius L.) are hematophagous pests present in urban environments across the globe. It is widely established that they have a strong host preference for humans. However, there are records of C. lectularius feeding upon a range of mammalian and avian hosts, including rodents, in the field. There is little information available about how frequently common bed bugs feed on alternative hosts in residential settings, but understanding this phenomenon has implications for both management of infestations and public health. Here, we examined cohorts of C. lectularius collected from 13 different dwellings in the state of New Jersey, USA, that were known to be simultaneously infested with house mice (Mus musculus domesticus). Host-specific quantitative polymerase chain reaction (qPCR) was used to determine if blood meals were taken from mice, while 16S rRNA gene amplicon sequencing was used to screen the bed bugs for the presence of zoonotic bacterial pathogens. We found no evidence that any of the bed bugs we collected fed on mice. Furthermore, the insects harbored depauperate bacterial communities that did not include known human pathogens. However, host-specific qPCR detected feline DNA in a pool of bed bugs from one dwelling, suggesting that interaction with domestic pets should be further investigated. Although sampling in this study was limited, the approach described herein will be useful for additional studies of the interactions between bed bugs and alternative blood meal hosts.

The Role of Antennae in Heat Detection and Feeding Behavior in the Bed Bug (Hemiptera: Cimicidae)

The common bed bug (Cimex lectularius L.) is an obligate hematophagous ectoparasite that has significant impacts on human health and well-being. All life stages of bed bugs (except eggs) feed solely on blood, which is required to molt and reproduce. Bed bugs use multiple cues to locate their hosts, including heat, CO2, and body odors. Of these cues, detection of heat appears limited to a short distance of <3 cm. However, it remains unclear if bed bugs can detect radiant heat, what structure(s) are responsible for heat detection, and if heat detection via the antennae is required for feeding. In this study, bed bug response to radiant heat was evaluated using the two-choice T-maze assay with the heat source either in contact with the surface (i.e., conduction) or not in contact (i.e., radiation) in nonantennectomized bed bugs. Further, we systematically ablated the bed bug's antennal segments (distal tip, first segment, and all four segments) and assessed their responses to heat and feeding in a unique two-choice T-maze assay and individual feeding assays, respectively. Our two-choice assays with contact to or no contact with the surface indicated that bed bugs cannot detect radiant heat. Later, we found that the distal tip of the terminal antennal segment is responsible for orientation toward a heat source. However, >50% of the bed bugs fed even when the entire antenna was removed, suggesting redundancy in sensory cues that drive feeding. These results will be used to better understand the role heat plays in bed bug host attraction and design of traps.