Impact of sublethal exposure to a pyrethroid-neonicotinoid insecticide on mating, fecundity and development in the bed bug Cimex lectularius L. (Hemiptera: Cimicidae).

Sublethal exposure to an insecticide may alter insect feeding, mating, oviposition, fecundity, development, and many other life history parameters. Such effects may have population-level consequences that are not apparent in traditional dose-mortality evaluations. Earlier, we found that a routinely used combination insecticide that includes a pyrethroid and a neonicotinoid (Temprid® SC) had deleterious effects on multiple bed bug (Cimex lectularius, L.) behaviors. Here, we demonstrate that sublethal exposure impacts physiology and reproduction as well. We report that sublethal exposure to Temprid SC has variable aberrant effects on bed bugs depending on the strain, including: a reduction in male mating success and delayed oviposition by females. However, after sublethal exposure, egg hatch rate consistently declined in every strain tested, anywhere from 34%-73%. Conversely, impact on fifth instar eclosion time was not significant. While the strains that we tested varied in their respective magnitude of sublethal effects, taken together, these effects could reduce bed bug population growth. These changes in bed bug behavior and fecundity could lead to improved efficacy of Temprid SC in the field, but recovery of impacted bugs must be considered in future studies. Sublethal effects should not be overlooked when evaluating insecticide efficacy, as it is likely that other products may also have indirect effects on population dynamics that could either aid or inhibit successful management of pest populations.

Behavioral effects of sublethal exposure to a combination of ß-cyfluthrin and imidacloprid in the bed bug, Cimex lectularius L.

BACKGROUND: Bed bugs (Cimex lectularius) are blood-feeding insect pests with public health relevance. Their rapid evolution of resistance to pyrethroids has prompted a shift to combination products that include both a pyrethroid and neonicotinoid insecticide. Insecticides have both a direct impact on mortality and an indirect effect on behavior. Thus, we assessed the sublethal effects of a widely used combination product containing ß-cyfluthrin (a pyrethroid) and imidacloprid (a neonicotinoid), as unexpected behavioral changes after exposure have been known to affect efficacy of insecticides. RESULTS: We found that bed bugs exposed to sublethal doses of a combination product containing ß-cyfluthrin and imidacloprid did not feed as effectively as untreated bugs. Their locomotion behavior was also reduced. However, aggregation in response to the presence of conspecific harborages was not affected by sublethal exposure. CONCLUSION: Bed bugs exhibit behavioral changes after sublethal exposure to a combination product that could affect pest management choices and outcomes. A reduction in host-finding efficiency and feeding could complement the lethal effects of the insecticide. Alternatively, reduced locomotion following exposure could limit ongoing contact with insecticide deposits. However, an overall reduction in movement indicates that treatments are unlikely to cause dispersal of bugs to adjacent dwellings. © 2016 Society of Chemical Industry.

Insecticide resistance in the bed bug comes with a cost.

Adaptation to new environmental stress is often associated with an alteration of one or more life history parameters. Insecticide resistant populations of insects often have reduced fitness relative to susceptible populations in insecticide free environments. Our previous work showed that three populations of bed bugs, Cimex lectularius L., evolved significantly increased levels of resistance to one product containing both ß-cyfluthrin and imidacloprid insecticides with only one generation of selection, which gave us an opportunity to explore potential tradeoffs between life history parameters and resistance using susceptible and resistant strains of the same populations. Life history tables were compiled by collecting weekly data on mortality and fecundity of bugs from each strain and treatment throughout their lives. Selection led to a male-biased sex ratio, shortened oviposition period, and decreased life-time reproductive rate. Generation time was shortened by selection, a change that represents a benefit rather than a cost. Using these life history characteristics we calculated that there would be a 90% return to pre-selection levels of susceptibility within 2- 6.5 generations depending on strain. The significant fitness costs associated with resistance suggest that insecticide rotation or utilization of non-insecticidal control tactics could be part of an effective resistance management strategy.

Population variation in and selection for resistance to pyrethroid-neonicotinoid insecticides in the bed bug.

Pyrethroid resistance in bed bugs, Cimex lectularius, has prompted a change to combination products that include a pyrethroid and a neonicotinoid. Ten populations of bed bugs were challenged with two combination products (Temprid SC and Transport GHP). Susceptibility of these populations varied, with the correlated response of the two products indicating cross resistance. We imposed selection on three populations using label rate Temprid, and then reared progeny from unselected and selected strains. All selected strains were significantly less susceptible to Temprid SC than unselected strains. Temprid selected strains were also less susceptible to Transport. The pyrethroid component of Temprid showed a significantly higher LD50 in selected strains, but susceptibility to the neonicotinoid remained unchanged. Taken together these results indicate resistance to combination insecticides is present in field populations at levels that should be of concern, and that short-term selection affecting existing variance in susceptibility can quickly increase resistance.

Entrapment of bed bugs by leaf trichomes inspires microfabrication of biomimetic surfaces.

Resurgence in bed bug infestations and widespread pesticide resistance have greatly renewed interest in the development of more sustainable, environmentally friendly methods to manage bed bugs. Historically, in Eastern Europe, bed bugs were entrapped by leaves from bean plants, which were then destroyed; this purely physical entrapment was related to microscopic hooked hairs (trichomes) on the leaf surfaces. Using scanning electron microscopy and videography, we documented the capture mechanism: the physical impaling of bed bug feet (tarsi) by these trichomes. This is distinct from a Velcro-like mechanism of non-piercing entanglement, which only momentarily holds the bug without sustained capture. Struggling, trapped bed bugs are impaled by trichomes on several legs and are unable to free themselves. Only specific, mechanically vulnerable locations on the bug tarsi are pierced by the trichomes, which are located at effective heights and orientations for bed bug entrapment despite a lack of any evolutionary association. Using bean leaves as templates, we microfabricated surfaces indistinguishable in geometry from the real leaves, including the trichomes, using polymers with material properties similar to plant cell walls. These synthetic surfaces snag the bed bugs temporarily but do not hinder their locomotion as effectively as real leaves.

Bed bugs evolved unique adaptive strategy to resist pyrethroid insecticides.

Recent advances in genomic and post-genomic technologies have facilitated a genome-wide analysis of the insecticide resistance-associated genes in insects. Through bed bug, Cimex lectularius transcriptome analysis, we identified 14 molecular markers associated with pyrethroid resistance. Our studies revealed that most of the resistance-associated genes functioning in diverse mechanisms are expressed in the epidermal layer of the integument, which could prevent or slow down the toxin from reaching the target sites on nerve cells, where an additional layer of resistance (kdr) is possible. This strategy evolved in bed bugs is based on their unique morphological, physiological and behavioral characteristics and has not been reported in any other insect species. RNA interference-aided knockdown of resistance associated genes showed the relative contribution of each mechanism towards overall resistance development. Understanding the complexity of adaptive strategies employed by bed bugs will help in designing the most effective and sustainable bed bug control methods.

Effects of juvenile hormone analog formulations on development and reproduction in the bed bug Cimex lectularius (Hemiptera: Cimicidae).

BACKGROUND: Bed bugs (Cimex lectularius L.) have become a common insect pest in urban areas and are often difficult to manage. Eradication is made more problematic by widespread insecticide resistance, raising interest in alternative control products. Juvenile hormone analogs (JHAs) such as methoprene and hydroprene are relatively harmless to non-arthropods and have proved to be effective against other urban insect pests. Two JHA products (Gentrol(®) and Precor(®), Central Life Sciences, Schaumburg, IL) were tested for efficacy against various bed bug stages as direct spray and as dry residue using three bed bug strains. RESULTS: At 1× and 2× the label rate, Precor(®) [active ingredient (S)-methoprene] had no significant effect on the development or fecundity of bed bugs. At 2× the label rate, confinement to residues of Gentrol(®) [active ingredient (S)-hydroprene] had no significant effect, but residues at 3× and 10× the label rate caused a reduction in fecundity and impaired development. Field strains were more susceptible to the reproductive effects of (S)-hydroprene than a long-maintained laboratory strain. CONCLUSIONS: While JHAs are attractive alternatives for pest management because of their inherent safety and distinct mode of action, these JHA formulations would have little impact on bed bug populations without relabeling to allow for higher application rates.

RNA interference of NADPH-cytochrome P450 reductase results in reduced insecticide resistance in the bed bug, Cimex lectularius.

BACKGROUND: NADPH-cytochrome P450 reductase (CPR) plays a central role in cytochrome P450 action. The genes coding for P450s are not yet fully identified in the bed bug, Cimex lectularius. Hence, we decided to clone cDNA and knockdown the expression of the gene coding for CPR which is suggested to be required for the function of all P450s to determine whether or not P450s are involved in resistance of bed bugs to insecticides. METHODOLOGY/PRINCIPAL FINDINGS: The full length Cimex lectularius CPR (ClCPR) cDNA was isolated from a deltamethrin resistant bed bug population (CIN-1) using a combined PCR strategy. Bioinformatics and in silico modeling were employed to identify three conserved binding domains (FMN, FAD, NADP), a FAD binding motif, and the catalytic residues. The critical amino acids involved in FMN, FAD, NADP binding and their putative functions were also analyzed. No signal peptide but a membrane anchor domain with 21 amino acids which facilitates the localization of ClCPR on the endoplasmic reticulum was identified in ClCPR protein. Phylogenetic analysis showed that ClCPR is closer to the CPR from the body louse, Pediculus humanus corporis than to the CPRs from the other insect species studied. The ClCPR gene was ubiquitously expressed in all tissues tested but showed an increase in expression as immature stages develop into adults. We exploited the traumatic insemination mechanism of bed bugs to inject dsRNA and successfully knockdown the expression of the gene coding for ClCPR. Suppression of the ClCPR expression increased susceptibility to deltamethrin in resistant populations but not in the susceptible population of bed bugs. CONCLUSIONS/SIGNIFICANCE: These data suggest that P450-mediated metabolic detoxification may serve as one of the resistance mechanisms in bed bugs.

Bed bug deterrence.

A recent study in BMC Biology has determined that the immature stage of the bed bug (the nymph) signals its reproductive status to adult males using pheromones and thus avoids the trauma associated with copulation in this species. The success of this nymphal strategy of deterrence is instructive. Against the background of increasing problems with bed bugs, this research raises the question whether pheromones might be used to control them. See research article http://www.biomedcentral.com/1741-7007/8/121.

Evaluation of chlorfenapyr for control of the bed bug, Cimex lectularius L.

BACKGROUND: The presence of bed bug populations resistant to pyrethroids demands the development of new control tactics, including the use of insecticides with new modes of action. Insecticides that disrupt oxidative phosphorylation in insect mitochondria can be an option. Laboratory assays were used to measure the toxicity of chlorfenapyr to susceptible strains and two strains highly resistant to pyrethroids. The effectiveness of two chlorfenapyr-based formulations was compared, and behavioral responses of bed bugs to dry residues of aerosol sprays were evaluated. RESULTS: Chlorfenapyr was effective against all bed bug strains, killing them at a similar rate, regardless of their susceptibility status to pyrethroids. Dry residues aged for 4 months were as toxic as fresh dry residues. The aerosol formulation had contact activity and caused faster mortality than a water-based formulation. Bed bugs did not avoid resting on surfaces treated with aerosol. CONCLUSION: Chlorfenapyr is an option for controlling pyrethroid-resistant bed bugs. While it does not cause quick knockdown, its long residual activity and no avoidance behavior of bed bugs to dry residues appear to make this insecticide suitable for bed bug control. A faster insecticidal effect is obtained with the aerosol formulation, suggesting greater bioavailability of the toxicant.

Circadian rhythm of spontaneous locomotor activity in the bed bug, Cimex lectularius L.

Bed bugs must avoid detection when finding hosts and returning to hidden harborages. Their stealthy habits include foraging when hosts are asleep. Characteristics of spontaneous locomotor activity rhythm of bed bugs with different feeding histories were studied. In the absence of host stimuli, adults and nymphs were much more active in the dark than in the light. The onset of activity in the scotophase commenced soon after lights-off. The free-running period (tau) for all stages was longer in continuous darkness (DD) than in continuous light (LL). The lengthening of tau in DD is an exception for the circadian rule that predicts the opposite in nocturnal animals. Activity in all stages was entrained to reverse L:D regimes within four cycles. Short-term starved adults moved more frequently than recently fed adults. While bed bugs can survive for a year or more without a blood meal, we observed a reduction in activity in insects held for five weeks without food. We suggest that bed bugs make a transition to host-stimulus dependent searching when host presence is not predictable. Such a strategy would enable bed bugs to maximize reproduction when resources are abundant and save energy when resources are scarce.

Widespread distribution of knockdown resistance mutations in the bed bug, Cimex lectularius (Hemiptera: Cimicidae), populations in the United States.

We previously reported high deltamethrin resistance in bed bugs, Cimex lectularius, collected from multiple areas of the United States (Romero et al., 2007). Recently, two mutations, the Valine to Leucine mutation (V419L) and the Leucine to Isoleucine mutation (L925I) in voltage-gated sodium channel alpha-subunit gene, had been identified to be responsible for knockdown resistance (kdr) to deltamethrin in bed bugs collected from New York (Yoon et al., 2008). The current study was undertaken to investigate the distribution of these two kdr mutations in 110 bed bug populations collected in the United States. Out of the 17 bed bug populations that were assayed for deltamethrin susceptibility, two resistant populations collected in the Cincinnati area and three deltamethrin-susceptible lab colonies showed neither of the two reported mutations (haplotype A). The remaining 12 populations contained L925I or both V419L and L925I mutations in voltage-gated sodium channel alpha-subunit gene (haplotypes B&C). In 93 populations that were not assayed for deltamethrin susceptibility, 12 contained neither of the two mutations (haplotype A) and 81 contained L925I or V419L or both mutations (haplotypes B-D). Thus, 88% of the bed bug populations collected showed target-site mutations. These data suggest that deltamethrin resistance conferred by target-site insensitivity of sodium channel is widely spread in bed bug populations across the United States.

Behavioral responses of the bed bug to insecticide residues.

The recent resurgence of bed bugs, Cimex lectularius L. (Heteroptera: Cimicidae), has increased the demand for information about effective control tactics. Several studies have focused on determining the susceptibility of bed bug populations to insecticides. However, behavioral responses of bed bugs to insecticide residues could influence their efficacy. The behavioral responses of bed bugs to deltamethrin and chlorfenapyr, two commonly used insecticides for bed bug control in the United States, were evaluated. In two-choice tests, grouped insects and individual insects avoided resting on filter paper treated with deltamethrin. Insects did not avoid surfaces treated with chlorfenapyr. Harborages, containing feces and eggs and treated with a deltamethrin-based product, remained attractive to individuals from a strain resistant to pyrethroids. Video recordings of bed bugs indicated that insects increased activity when they contacted sublethal doses of deltamethrin. Insecticide barriers of chlorfenapyr or deltamethrin did not prevent bed bugs from reaching a warmed blood source and acquiring blood meals. We discuss the impact of these responses on bed bug control practices.

Evaluation of piperonyl butoxide as a deltamethrin synergist for pyrethroid-resistant bed bugs.

An understanding of the mechanisms of insecticide resistance in the bed bug, Cimex lectularius L., has the potential to lead to new approaches for the control of resistant populations. We used the cytochrome P450 monooxygenase (P450) inhibitor piperonyl butoxide (PBO) to assess the role of P450s in deltamethrin resistance in three field-collected bed bug strains, LA-1, CIN-1 and WOR-1. In addition, we exposed two highly resistant strains, CIN-1 and WOR-1 (resistance ratio [RR] >2,500-fold), to dry residues of piperonyl butoxide-synergized pyrethroid formulations to determine the utility of synergism by PBO. Piperonyl butoxide synergized deltamethrin in all three strains, but its impact was variable. The synergistic ratio varied from 40 in CIN-1 to 176 in WOR-1. Because the resistance ratio for each strain after piperonyl butoxide treatment was 174 and 39, respectively, our results suggest that P450s have some involvement in deltamethrin resistance, but other resistance mechanisms must be involved as well. No significant synergistic effect of formulated deltamethrin was observed with the addition of synergized pyrethrins or formulated piperonyl butoxide in the CIN-1 strain, but synergism occurred in the WOR-1 strain. Addition of PBO to pyrethroids is not a comprehensive solution to pyrethroid resistance because strains vary in both overall resistance level and the proportion of that resistance attributable to P450s.

Insecticide resistance in the bed bug: a factor in the pest's sudden resurgence?

Infestations of the bed bug, Cimex lectularius L. (Heteroptera: Cimicidae), are increasing around the world at an alarming rate and have become a major public health concern. The evolution of insecticide resistance could be a primary factor in explaining this resurgence. Extremely high levels of resistance to two pyrethroid insecticides, deltamethrin and lambda-cyhalothrin, relative to a susceptible colony, were detected in populations collected from human dwellings in Kentucky and Ohio. Offspring of a cross between a resistant and susceptible colony had intermediate susceptibility. Evaluations of populations from across the United States indicate that resistance to pyrethroid insecticides is already widespread. Without the development of new tactics for bed bug management, further escalation of this public health problem should be expected.

Ladybug hypersensitivity among residents of homes infested with ladybugs in Kentucky.

BACKGROUND: There have been isolated case reports of hypersensitivity to the ladybug species Harmonia axyridis. Entomologists now report a rapid increase in ladybug numbers, giving rise to increasing complaints of residential infestations. OBJECTIVES: To determine whether ladybug infestation of homes causes hypersensitivity among residents and to estimate the prevalence of self-reported ladybug allergy in this population. METHODS: This pilot observational study was conducted using an anonymous survey. RESULTS: The participation rate was 59% (99/167). The incidence of self-reported allergy symptoms in this population was 77% (95% confidence interval [CI], 67%-85%). The prevalence of self-reported ladybug allergy was 50% (95% CI, 39%-60%). Of all the respondents, 19% (95% CI, 12%-28%) reported allergy symptoms on direct contact with ladybugs and 31% (95% CI, 22%-41%) reported the use of extra allergy medications during times of infestation. The correlation between worsening of allergy symptoms and time of infestation was significant for spring, fall, and winter infestations (P = .02, P = .001, and P < .001, respectively). CONCLUSIONS: To our knowledge, this is the first study to estimate the prevalence of ladybug hypersensitivity, which was found to be 50% by self-report among people with home infestations. These results suggest that the ladybug could be a significant cause of respiratory allergy in heavily infested homes. Further studies using diagnostic testing to confirm allergy are now indicated. We recommend that patients with spring, fall, and winter allergies be asked about ladybug infestation and that ladybug reagents be made available for diagnostic testing.