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

Ontogenesis of Aldehyde Pheromones in Two Synanthropic Bed Bug Species (Heteroptera: Cimicidae)

Bed bugs produce volatile aldehydes that have alarm and aggregation functions. Using two synanthropic bed bug species, Cimex lectularius L. and C. hemipterus (Fabricius), developmental changes were examined for (E)-2-hexenal, 4-oxo-(E)-2-hexenal, (E)-2-octenal, and 4-oxo-(E)-2-octenal, the four most abundant aldehydes shared between the two species. Quantitative analyses of the aldehydes in the nymphal exuviae indicated that the aldehydes' ratio remained similar throughout nymphal development. In general, (E)-2-octenal was most abundant, and (E)-2-hexenal and 4-oxo-(E)-2-octenal were least abundant. The fourth aldehyde, 4-oxo-(E)-2-hexenal, was present in intermediate quantities. The quantities and percent abundances of the aldehydes in nymphal exuviae and the adults were significantly different between C. lectularius and C. hemipterus. The ratio between (E)-2-hexenal and (E)-2-octenal was determined in adult male and female bed bugs of each species. Adult C. hemipterus had a higher proportion of (E)-2-hexenal than C. lectularius, while no sex differences were found. This work provides the first systematic quantification of four aldehydes [(E)-2-hexenal, 4-oxo-(E)-2-hexenal, (E)-2-octenal and 4-oxo-(E)-2-octenal] for all five of the nymphal stages for both C. lectularius and C. hemipterus.

Infestation Pattern and Population Dynamics of the Tropical Bed Bug, Cimex hemipterus (F.) (Hemiptera: Cimicidae) Based on Novel Microsatellites and mtDNA Markers

The tropical bed bug, Cimex hemipterus (F.), has now emerged as an important public health pest in the tropics. Despite its alarming infestation rate, the information on its population genetics remains scarce. Here, we described the infestation structure and population dynamics of C. hemipterus in the tropics, especially Malaysia and Singapore, based on eight novel microsatellites and two mtDNA markers, including cytochrome c oxidase I (COI) and 16S rRNA genes. Across populations, microsatellite data revealed high genetic diversity with significant genetic differentiation and restricted gene flow. Analysis within populations revealed evidence of a recent bottleneck. Nonetheless, elevated genetic diversity in nearly all populations suggests that the propagule in C. hemipterus populations were much diverse, distantly related (mean r = 0.373), and not significantly inbred (mean F_IS = 0.24) than that observed in Cimex lectularius from previous studies. We observed seven mtDNA haplotypes across the 18 populations studied (Hd = 0.593) and several populations displayed more than one matrilineal descent. The two markers were generally congruent in suggesting a common, genetically diverse (especially at the nuclear region) source population with possibilities of multiple introductions for the bed bug populations in the present study.

Insecticide resistance mechanisms with novel 'kdr' type gene mutations in the tropical bed bug Cimex hemipterus

BACKGROUND

The tropical bed bug, Cimex hemipterus, is a serious indoor public health pest in tropical regions causing intense physical discomfort and mental distress to humans. At present, the application of insecticides is the major control strategy. The present study was designed to evaluate the development of resistance and resistance mechanisms in Cimex hemipterus from Kandy district, Sri Lanka.

METHODS

The resistance status of the collected bed bugs was determined against the discriminative dosages of DDT, malathion, propoxur, deltamethrin and permethrin by conducting bioassays according to World Health Organization guidelines. Activities of insecticide metabolizing enzymes, i.e. esterases, glutathione S-transferases (GST) and monooxygenases, and the insensitivity of organophosphate/carbamate target site acetylcholinesterase (AChE), were evaluated by biochemical assays. Regions of the gene of the pyrethroid/DDT target site, the voltage-gated sodium channel regulatory protein (VGSC), were sequenced for possible kdr mutations.

RESULTS

Survival percentages of bed bug population were 71, 68 and 51% for DDT, malathion and propoxur respectively. KT50 and KT90 values, calculated using log-probit mortality curves for deltamethrin were 62.55 and 123.96 h, respectively. These values were much higher for permethrin where KT50 was 201.10 h and the KT90 was beyond the detectable range. Results were compared with previous values reported for the same population in 2002. Resistance to propoxur has increased significantly from 11 to 51% with about a 20-fold increase in the number of individuals with elevated esterase mechanism. No significant change has occurred in malathion and DDT resistance, in GST and monooxygenase activities, and in AChE sensitivity for the past 14 years. Six kdr associated mutations (Y/L995H, V1010L, I1011F, L1014F, V1016E, L1017F/S) and a non-kdr associated mutation (A1007S mutation) were found from the α-region of the VGSC gene. Out of the kdr type mutations, only L1014F has been reported previously form C. hemipterus while the others have been reported from other insects.

CONCLUSIONS

The bed bug population has developed high resistance to propoxur with increased esterase activities. KT50 for deltamethrin and permethrin has increased 125- and 20-fold, respectively, over the period 2002 to 2016. To the authors' knowledge, this is the first time that the possible involvement of a kdr type mutation in developing pyrethroid resistance in C. hemipterus has been shown in Sri Lanka.

Aggregation behavior and reproductive compatibility in the family Cimicidae

Bed bugs (Cimex lectularius) provide a unique opportunity to understand speciation and host-associated divergence in parasites. Recently, two sympatric but genetically distinct lineages of C. lectularius were identified: one associated with humans and one associated with bats. We investigated two mechanisms that could maintain genetic differentiation in the field: reproductive compatibility (via mating crosses) and aggregation fidelity (via two-choice sheltering assays). Effects were assessed at the intra-lineage level (within human-associated bed bugs), inter-lineage level (between human- and bat-associated bed bugs), and inter-species level (between C. lectularius and Cimex pipistrelli [bat bug]). Contrary to previous reports, bed bugs were found to be reproductively compatible at both the intra- and inter-lineage levels, but not at the inter-species level (although three hybrids were produced, one of which developed into an adult). Lineage- and species-specific aggregation fidelity was only detected in 8% (4 out of 48) of the aggregation fidelity assays run. These results indicate that under laboratory conditions, host-associated lineages of bed bugs are reproductively compatible, and aggregation pheromones are not capable of preventing gene flow between lineages.

Differences in Climbing Ability of Cimex lectularius and Cimex hemipterus (Hemiptera: Cimicidae)

The climbing abilities of two bed bug species, Cimex lectularius L. and Cimex hemipterus (F.), were determined by evaluating their escape rates from smooth surface pitfall traps using four commercial bed bug monitors (Verifi Bed Bug Detector, ClimbUp Insect Interceptor, BlackOut Bed Bug Detector, and SenSci Volcano Bed Bug Detector). All detectors were used in the absence of lures or attractants. Unlike C. lectularius, adult C. hemipterus were able to escape from all traps. On the other hand, no or a low number nymphs of both species escaped, depending on the evaluated traps. Examination of the vertical friction force of adults of both species revealed a higher vertical friction force in C. hemipterus than in C. lectularius. Scanning electron microscope micrograph observation on the tibial pad of adult bed bugs of C. hemipterus showed the presence of a greater number of tenent hairs on the tibial pad than on that of adult C. lectularius. No tibial pad was found on the fourth and fifth instars of both species. Near the base of the hollow tenent hairs is a glandular epithelium that is better developed in adult C. hemipterus than in adult C. lectularius. This study highlights significant morphological differences between C. lectularius and C. hemipterus, which may have implications in the monitoring and management of bed bug infestations.

Bed bugs: clinical relevance and control options

Since the late 1990s, bed bugs of the species Cimex lectularius and Cimex hemipterus have undergone a worldwide resurgence. These bed bugs are blood-sucking insects that readily bite humans. Cutaneous reactions may occur and can start out as small macular lesions that can develop into distinctive wheals of around 5 cm in diameter, which are accompanied by intense itching. Occasionally, bullous eruptions may result. If bed bugs are numerous, the patient can present with widespread urticaria or eythematous rashes. Often, bites occur in lines along the limbs. Over 40 pathogens have been detected in bed bugs, but there is no definitive evidence that they transmit any disease-causing organisms to humans. Anemia may result when bed bugs are numerous, and their allergens can trigger asthmatic reactions. The misuse of chemicals and other technologies for controlling bed bugs has the potential to have a deleterious impact on human health, while the insect itself can be the cause of significant psychological trauma. The control of bed bugs is challenging and should encompass a multidisciplinary approach utilizing nonchemical means of control and the judicious use of insecticides. For accommodation providers, risk management procedures should be implemented to reduce the potential of bed bug infestations.

Surface contact toxicity and synergism of several insecticides against different stages of the tropical bed bug, Cimex hemipterus (Hemiptera: Cimicidae)

BACKGROUND

Five formulated insecticides (lambda-cyhalothrin at 10 mg m⁻², bifenthrin at 50 mg m⁻², fipronil at 10 mg m⁻², fenitrothion at 50 mg m⁻², imidacloprid at 5 mg m⁻²) and one active ingredient (DDT at 500 mg m⁻²) were evaluated using a surface contact method against early and late instars and adults of two strains of the tropical bed bug, Cimex hemipterus (F.). Synergism of lambda-cyhalothrin and fipronil using piperonyl butoxide (PBO) was also assessed.

RESULTS

The order of susceptibility of different stages of bed bugs was as follows: early stage-lambda-cyhalothrin > bifenthrin = imidacloprid > fipronil > fenitrothion > DDT; late stage-lambda-cyhalothrin > bifenthrin > fenitrothion > imidacloprid > fipronil > DDT; adult-lambda-cyhalothrin > imidacloprid > bifenthrin > fenitrothion > fipronil > DDT. The late instars exhibited significantly higher LT₅₀ among the life stages. The addition of PBO to fipronil increased the susceptibility of the insects.

CONCLUSIONS

Lambda-cyhalothrin, bifenthrin, fenitrothion and fipronil at the recommended application rates were effective against C. hemipterus. Although imidacloprid demonstrated good initial response against C. hemipterus, the insects showed substantial recovery 72 h post-treatment. The late instars (fourth and fifth instars) should be used as the model for toxicological evaluation.