The Odorant Receptor Co-Receptor from the Bed Bug,Cimex lectularius L

Recently, the bed bug, Cimex lectularius L. has re-emerged as a serious and growing problem in many parts of the world. Presence of resistant bed bugs and the difficulty to eliminate them has renewed interest in alternative control tactics. Similar to other haematophagous arthropods, bed bugs rely on their olfactory system to detect semiochemicals in the environment. Previous studies have morphologically characterized olfactory organs of bed bugs’ antenna and have physiologically evaluated the responses of olfactory receptor neurons (ORNs) to host-derived chemicals. To date, odorant binding proteins (OBPs) and odorant receptors (ORs) associated with these olfaction processes have not been studied in bed bugs. Chemoreception in insects requires formation of heteromeric complexes of ORs and a universal OR coreceptor (Orco). Orco is the constant chain of every odorant receptor in insects and is critical for insect olfaction but does not directly bind to odorants. Orco agonists and antagonists have been suggested as high-value targets for the development of novel insect repellents. In this study, we have performed RNAseq of bed bug sensory organs and identified several odorant receptors as well as Orco. We characterized Orco expression and investigated the effect of chemicals targeting Orco on bed bug behavior and reproduction. We have identified partial cDNAs of six C. lectularius OBPs and 16 ORs. Full length bed bug Orco was cloned and sequenced. Orco is widely expressed in different parts of the bed bug including OR neurons and spermatozoa. Treatment of bed bugs with the agonist VUAA1 changed bed bug pheromone-induced aggregation behavior and inactivated spermatozoa. We have described and characterized for the first time OBPs, ORs and Orco in bed bugs. Given the importance of these molecules in chemoreception of this insect they are interesting targets for the development of novel insect behavior modifiers.     

Competence of Cimex lectularius Bed Bugs for the Transmission of Bartonella quintana,the Agent of Trench Fever

Background Bartonella quintana, the etiologic agent of trench fever and other human diseases, is transmitted by the feces of body lice. Recently, this bacterium has been detected in other arthropod families such as bed bugs, which begs the question of their involvement in B. quintana transmission. Although several infectious pathogens have been reported and are suggested to be transmitted by bed bugs, the evidence regarding their competence as vectors is unclear.ConclusionThe present work demonstrated for the first time that bed bugs can acquire, maintain for more than 2 weeks and release viable B. quintana organisms following a stercorarial shedding. We also observed the vertical transmission of the bacterium to their progeny. Although the biological role of bed bugs in the transmission of B. quintana under natural conditions has yet to be confirmed, the present work highlights the need to reconsider monitoring of these arthropods for the transmission of human pathogens.     

Role of Vision and Mechanoreception in Bed Bug,Cimex lectularius L. Behavior

The role of olfactory cues such as carbon dioxide, pheromones, and kairomones in bed bug, Cimex lectularius L. behavior has been demonstrated. However, the role of vision and mechanoreception in bed bug behavior is poorly understood. We investigated bed bug vision by determining their responses to different colors, vertical objects, and their ability to detect colors and vertical objects under low and complete dark conditions. Results show black and red paper harborages are preferred compared to yellow, green, blue, and white harborages. A bed bug trapping device with a black or red exterior surface was significantly more attractive to bed bugs than that with a white exterior surface. Bed bugs exhibited strong orientation behavior toward vertical objects. The height (15 vs. 30 cm tall) and color (brown vs. black) of the vertical object had no significant effect on orientation behavior of bed bugs. Bed bugs could differentiate color and detect vertical objects at very low background light conditions, but not in complete darkness. Bed bug preference to different substrate textures (mechanoreception) was also explored. Bed bugs preferred dyed tape compared to painted tape, textured painted plastic, and felt. These results revealed that substrate color, presence of vertical objects, and substrate texture affect host-seeking and harborage-searching behavior of bed bugs. Bed bugs may use a combination of vision, mechanoreception, and chemoreception to locate hosts and seek harborages.     

The comparative toxicity of various contact insecticides to the louse (Pediculus humanus L.) and the bed-bug (Cimex lectularius L.)

A variety of substances has been tested by laboratory methods as insecticides against the bed-bug and the body-louse. The oil-soluble samples were tested by the Potter tower method which gave the most accurate results. Certain liquids were tested by a simple dipping method, and solids insoluble in mineral oils were tested as aqueous solutions by the dipping method or as dusts.
Various organic thiocyanates were found to show similar relative toxicity to the louse and bug, but the pyrethrins were much more toxic to the latter. D.D.T. was highly toxic to both and Gammexane even more insecticidal, especially to the louse.
In the dipping tests, two types of toxic action were observed: an immediate physicochemical action and a delayed lethal action due to asphyxiation. Refined mineral oils kill lice by the latter method. Among the aqueous preparations, the emulsion of cresols known as Lysol was noteworthy for its ovicidal powers.
Some experiments were made with extracts of delphinium seeds, the insecticidal powers of which were shown to reside in the alkaloids.     

Production of a hybrid between the bedbugs Cimex hemipterus and Cimex lectularius

Of 479 eggs laid by female Cimex lectularius Linnaeus and C.hemipterus (Fabricius) mated by males of the other species, one was fertile and gave rise to a first stage nymph. The egg showed sculpturing typical of C.hemipterus, the female parent, and the nymph conformed to the narrow pronotum and abdomen of this species, being significantly different from C.lectularius in the width of the abdomen. Because the orientation and lengths of the bristles on the sides of the abdomen were distinctly different from C.hemipterus and closely resembled C.lectularius, the single nymph obtained from the cross C.hemipterus x lectularius was interpreted as being a hybrid rather than a product of parthenogenesis.     

A 454 Survey Reveals the Community Composition and Core Microbiome of the Common Bed Bug (Cimex lectularius) across an Urban Landscape

Elucidating the spatial dynamic and core constituents of the microbial communities found in association with arthropod hosts is of crucial importance for insects that may vector human or agricultural pathogens. The hematophagous Cimex lectularius (Hemiptera: Cimicidae), known as the human bed bug, has made a recent resurgence in North America, as well as worldwide, potentially owing to increased travel, climate change and resistance to insecticides. A comprehensive survey of the bed bug microbiome has not been performed to date, nor has an assessment of the spatial dynamics of its microbiome. Here we present a survey of internal and external bed bug microbial communities by amplifying the V4–V6 hypervariable region of the 16S rDNA gene region followed by 454 Titanium sequencing using 31 individuals from eight distinct collection locations obtained from residences in Cincinnati, OH. Across all samples, 97% of the microbial community is made up of two dominant OTUs, previously identified as the α-proteobacterium Wolbachia and an unnamed γ-proteobacterium from the Enterobacteriaceae. Microbial communities varied among host locations for measures of community diversity and exhibited structure according to collection location. This broad survey represents the most in-depth assessment, to date, of the microbes that associate with bed bugs.     

Cuticle Thickening in a Pyrethroid-Resistant Strain of the Common Bed Bug,Cimex lectularius L. (Hemiptera: Cimicidae)

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.     

Effects of elevated temperature on the mycetome and symbiotes of the bed bug Cimex lectularius (Heteroptera)

High temperature treatment significantly reduced the reproductive rate of Cimex lectularius and simultaneously rendered their mycetomes nearly symbiote-free. The possibility that the symbiotes may affect host reproductive potential is discussed.     

Comparative transcriptomics of the bacteriome and the spermalege of the bedbug Cimex lectularius (Hemiptera: Cimicidae)

The bedbug Cimex lectularius is notorious as a blood-feeding exoparasite of human and other warm-blooded animals. In addition to its medical and hygienic importance, C. lectularius is known for its unique biological traits, including obligate nutritional mutualism with a vitamin-provisioning Wolbachia endosymbiont and a peculiar mating habit called traumatic insemination wherein male sperm is injected into the female body cavity, migrates to the ovary, and fertilizes eggs therein. For these unique traits, novel insect organs, the bacteriome for endosymbiosis and the spermalege for traumatic insemination, have evolved in the lineage of bedbugs. We constructed cDNA libraries of the bacteriome and the spermalege of C. lectularius, and performed expressed sequence tag (EST) analyses of these peculiar insect organs. In total 4480 ESTs were compiled, which were assembled into 2989 unique sequences (USs). The following ESTs and USs were identified from the different organs: 1151 ESTs and 901 USs from the female whole body; 1098 ESTs and 879 USs from the female bacteriome; 1145 ESTs and 783 USs from the male bacteriome; and 1086 ESTs and 920 USs from the female spermalege. These EST data will provide a valuable genetic resource for understanding the developmental and evolutionary aspects of these novel insect organs.     

Susceptibility of the bedbug,Cimex lectularius,to selected insecticides and various treated surfaces

Abstract. Adult bedbugs, Cimex lectularius, were exposed for 24 h (25^oC) to filter paper treated with various dilutions of the technical grade of nine insecticides dissolved in acetone to determine the concentration-response relationships. The order of toxicity, from most to least based on the LC₅₀'s was: dichlorvos, pirimiphos methyl, lambda-cyhalothrin, bendiocarb, permethrin, malathion, carbaryl, tetrachlorvinphos, and fenvalerate. The residual toxicities of commercial formulations of six of the chemicals diluted with water and applied to wood, cardboard, cloth and galvanized metal, were determined by exposing adult bedbugs at 3,7 and 12 weeks after treatment. The formulation of bendiocarb (FICAM® 76% W) had little residual activity on all surfaces at 12 weeks after treatment. The formulation of carbaryl (SEVIN® 21.5% L) was toxic to bedbugs on all surfaces at 12 weeks after treatment, but required high concentrations on wood, cardboard, and cloth. The formulation of pirimiphos methyl (ACTELLIC® 57% EC) had no residual activity on any of the surfaces at 12 weeks after treatment. The formulation of tetrachlorovinphos (RABON® 50% W) had residual activity for 12 weeks on all surfaces except metal. The formulation of permethrin (ATROBAN® 11% EC) had residual activity on only metal and wood while the formulation of lambda-cyhalothrin (KARATE® 13.1% EC) had residual activity 12 weeks on all surfaces.     

Extensive structural variations between mitochondrial genomes of CMS and normal peppers (Capsicum annuum L.) revealed by complete nucleotide sequencing

Background

Cytoplasmic male sterility (CMS) is an inability to produce functional pollen that is caused by mutation of the mitochondrial genome. Comparative analyses of mitochondrial genomes of lines with and without CMS in several species have revealed structural differences between genomes, including extensive rearrangements caused by recombination. However, the mitochondrial genome structure and the DNA rearrangements that may be related to CMS have not been characterized in Capsicum spp.

Results

We obtained the complete mitochondrial genome sequences of the pepper CMS line FS4401 (507,452 bp) and the fertile line Jeju (511,530 bp). Comparative analysis between mitochondrial genomes of peppers and tobacco that are included in Solanaceae revealed extensive DNA rearrangements and poor conservation in non-coding DNA. In comparison between pepper lines, FS4401 and Jeju mitochondrial DNAs contained the same complement of protein coding genes except for one additional copy of an atp6 gene (ψatp6-2) in FS4401. In terms of genome structure, we found eighteen syntenic blocks in the two mitochondrial genomes, which have been rearranged in each genome. By contrast, sequences between syntenic blocks, which were specific to each line, accounted for 30,380 and 17,847 bp in FS4401 and Jeju, respectively. The previously-reported CMS candidate genes, orf507 and ψatp6-2, were located on the edges of the largest sequence segments that were specific to FS4401. In this region, large number of small sequence segments which were absent or found on different locations in Jeju mitochondrial genome were combined together. The incorporation of repeats and overlapping of connected sequence segments by a few nucleotides implied that extensive rearrangements by homologous recombination might be involved in evolution of this region. Further analysis using mtDNA pairs from other plant species revealed common features of DNA regions around CMS-associated genes.

Conclusions

Although large portion of sequence context was shared by mitochondrial genomes of CMS and male-fertile pepper lines, extensive genome rearrangements were detected. CMS candidate genes located on the edges of highly-rearranged CMS-specific DNA regions and near to repeat sequences. These characteristics were detected among CMS-associated genes in other species, implying a common mechanism might be involved in the evolution of CMS-associated genes.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-561) contains supplementary material, which is available to authorized users.     

Competition for nutrients between Calluna vulgaris (L.) Hull and Molinia caerulea (L.) Moench

Summary A combination of a removal and fertilization experiment in the field and a replacement experiment in containers in a cold frame was carried out to investigate the role of nutrient supply in the interactions between Calluna vulgaris and Molinia caerulea. It is concluded that the growth of Calluna as well as that of Molinia increased with increasing nutrient availability. However, the increase in biomass of Molinia was much larger than that of Calluna. It is also concluded that increased nutrient availability favours the competitive vigour of Molinia in interaction with Calluna.