Journal of medical entomology最新文献

Insecticide resistance in Aedes aegypti (Linn., 1762) and Aedes albopictus (Skuse, 1894) has hindered efforts to control dengue outbreaks. Understanding resistance profiles and underlying mechanisms is essential to guide the selection of insecticides and synergists for operational use in northern and southern Taiwan. In this study, we conducted WHO-standard insecticide susceptibility assays, synergist-insecticide bioassays, and molecular diagnostics on field-collected Aedes populations to characterize resistance phenotypes and elucidate their mechanisms. Three pyrethroid insecticides: deltamethrin, permethrin, and lambda-cyhalothrin, and two non-pyrethroids: pirimiphos-methyl (organophosphate) and bendiocarb (carbamate), were tested. Aedes aegypti exhibited resistance to all three pyrethroids and pirimiphos-methyl. High frequencies of multiple simultaneous kdr mutations (S989P, V1016G, F1534C, and D1763Y), along with cytochrome P450 monooxygenase, significantly conferred the pyrethroid resistance in Ae. aegypti. All northern Ae. albopictus populations showed resistance to pyrethroids, although susceptibility to pirimiphos-methyl and bendiocarb varied among populations. The I1532V mutation was detected at low frequency and was not associated with pyrethroid resistance in these populations. Piperonyl butoxide (PBO) restored susceptibility in most Ae. albopictus populations, indicating a significant role of cytochrome P450 monooxygenases in conferring pyrethroid resistance. Furthermore, a significant correlation was found between the frequency of insecticide applications in local areas and reduced mosquito mortality, suggesting that chemical control practices exert selective pressure on Ae. albopictus -populations. This study reveals substantial variation in both resistance phenotypes and mechanisms between Ae. aegypti and Ae. albopictus in Taiwan. These findings underscore the need for adaptive vector control strategies to mitigate resistance development and sustain the efficacy of chemical interventions.

Mosquito control interventions are constrained by the limited availability of active ingredients. While there are already very few, the development of pesticide resistance further constrains the options. Innovation in biorational active ingredients is therefore critical for managing invasive vector mosquito species such as Aedes aegypti (L.) and Ae. albopictus (Skuse). Laboratory and semifield evaluations were conducted to compare the effectiveness and efficacy of the novel compounds S-methobutene with S-methoprene against these species. Laboratory bioassays showed that technical grade S-methobutene was 5.7- to 11.5-fold more active than S-methoprene against Ae. aegypti, and 7.5- to 12.7-fold more active against Ae. albopictus. When compared at equivalent active ingredient levels, S-methobutene granules exhibited 5.7- to 10.2-fold greater activity against Ae. aegypti and 5.8- to 12.3-fold greater activity against Ae. albopictus than S-methoprene granules. In semifield microcosm trials, 1.0% S-methobutene granules achieved efficacy comparable to that of 4.25% S-methoprene granules at the same application rates, confirming the superior performance of S-methobutene at lower concentrations as observed in the laboratory assays. Enhanced bioactivity of the technical grades in laboratory bioassays and the field efficacy of the granular formulations in microcosm tests demonstrated that the novel S-methobutene outperformed S-methoprene against mosquito species Ae. aegypti and Ae. albopictus.

In 2019, the Northeast Regional Center for Excellence in Vector-Borne Diseases (NEVBD) initiated a unique region-wide insecticide resistance monitoring program covering the Northeast and Mid-Atlantic United States regions. NEVBD evaluated 2 key mosquito vectors, Aedes albopictus Skuse [Diptera: Culicidae] and Culex pipiens L. [Diptera: Culicidae], for resistance to insecticides deployed against larval and adult mosquitoes. Additionally, Culex restuans Theobald [Diptera: Culicidae] mortality was assessed. Insecticide use surveys provided insights into the region's resistance monitoring capacity and insecticide usage. In response to these surveys, NEVBD developed susceptibility curves, diagnostic doses, and larval bioassays for regionally important larvicides. Adulticide resistance was assessed using CDC bottle bioassays. A total of 42 agencies submitted mosquitoes for testing, including Cx. pipiens (79%), Ae. albopictus (10%) and Cx. restuans (10%). Culex pipiens populations with moderate to high pyrethroid resistance were identified in several locations, along with emerging resistance to organophosphates in Virginia. Additionally, Cx. pipiens resistance to the larvicide methoprene was widespread, while no resistance to Bacillus thuringiensis israelensis (Bti) Berliner or Lysinibacillus sphaericus Meyer and Neide was detected. All Ae. albopictus submitted for larvicide testing were susceptible to Bti; but displayed low-level methoprene resistance. To empower regional partners to make informed vector control decisions, NEVBD's resistance data were made publicly available. In addition, organized training sessions and consultations were provided on resistance monitoring practices. Our results confirm the presence of multi-year region-wide insecticide resistance data for medically relevant mosquitoes across the Northeast and Mid-Atlantic states, highlighting the need for coordinated resistance monitoring and training to successfully protect public health.

The public health risk of ticks and tick-borne diseases (TBDs) have been steadily increasing, partly due to ticks expanding their range into human proximity. However, there is lack of up-to-date information on tick species composition in West Malaysia, particularly within high-risk ecosystems for tick exposure. This study investigates the presence of tick species in 6 ecosystems of Pahang and Terengganu, where human TBD cases have been reported, through morphological and molecular identification approaches. A total of 153 small mammals were caught, dominantly from recreational forest (RF), belonging to 13 species. Of these, 68 were infested with ticks, to make an overall prevalence of 44.4%. Additionally, a total of 351 individual of feeding and questing ticks were collected. A mix life stages of these ticks were then identified as Amblyomma cordiferum Neumann 1899, Amblyomma geoemydae (Cantor, 1847), Amblyomma testudinarium Koch 1844, Dermacentor auratus Supino 1897, Dermacentor compactus Neumann 1901, Dermacentor steini (Schulze, 1933), Dermacentor tricuspis (Schulze, 1933), Dermacentor sp., Haemaphysalis hystricis Supino 1897, Haemaphysalis sp., and Ixodes granulatus Supino 1897. The most prevalent species was D. auratus (43%), followed by D. steini (16%) and I. granulatus (12.3%). Interestingly, this study is the first to report high infestation of various developmental stages of ticks on Tupaia glis (Diard, 1820) in Malaysia, highlighting its potential as a competent host for both and ticks and pathogens. These findings offer valuable evidence for public health authorities and sheds new light on tick species in TBD-related ecosystems, which can be applied for tick-management programs in Malaysia.

Accurate estimation of the time of colonization (TOC) is a cornerstone of forensic entomology, yet direct validation of laboratory-derived development datasets in field contexts remains rare. Within validation studies, when the TOC is unknown, the time of placement (TOP)-the point at which remains become accessible to insects (e.g,. Diptera)-can serve as a proxy. This study evaluated the accuracy of Cochliomyia macellaria (Diptera: Calliphoridae) development estimates under varying ecological conditions by calculating the estimated-to-actual TOP ratio (%). Factors examined included carcass type (small, medium, and large mammals; large birds), thermal summation method (accumulated degree days [ADD] vs. accumulated degree hours [ADH]), emergence timing (first vs. last emergence), development dataset tissue source (porcine vs. equine), and species coexistence with Chrysomya rufifacies (Diptera: Calliphoridae). A full-factorial, aligned rank-transformed ANOVA was conducted using three replicates per carcass type across two Texas field sites in 2023 and 2024. Using ADD, first-emergence data, and porcine-derived tissue consistently yielded the highest TOP ratios (93.9%, 96.3%, and 93.4%, respectively). Precision was greatest in small mammals and lowest in large mammals. Although ADD-based estimates generally outperformed ADH, ADH occasionally demonstrated greater consistency under certain contexts. Species coexistence and trial year showed context-dependent influences on TOP ratio outcomes. These findings underscore the importance of incorporating ecological and biological variability when applying development studies to forensic casework and highlight the robustness of ADD calculations and early-emergence sampling for estimating TOC in the field.

The blacklegged tick (Ixodes scapularis) is a primary vector of medical concern in the eastern United States, capable of infesting a wide range of hosts. The first established population in Ohio was detected on rural residential properties in Coshocton County and has since expanded across the state. To assess current conditions, these index sites were revisited, and questing ticks were collected between 2019 and 2021, with small mammals sampled in 2021. Ticks and host tissues were screened for Borrelia burgdorferi sensu lato, Borrelia burgdorferi sensu stricto, Borrelia mayonii, and Anaplasma phagocytophilum. A total of 654 questing blacklegged ticks and 106 small mammals representing eight species were sampled. White-footed mice (Peromyscus leucopus) and eastern chipmunks (Tamias striatus) were the most frequently infested hosts. Infection prevalence in ticks was 47.6% for B. burgdorferi sensu lato, 42.9% for B. burgdorferi sensu stricto, and 15.5% for A. phagocytophilum. Six of eight small mammal species tested positive, with infection prevalence of 60.4%, 19.8%, and 11.9% for the same pathogens, respectively. Borrelia mayonii was not detected. These infection prevalences are comparable to those reported in long-established Lyme-endemic regions in the northeastern and upper midwestern United States. Findings indicate that the enzootic Lyme disease cycle is now well established in parts of Ohio. Public health agencies should be aware of the increasing risk of tick-borne disease in the region, and these results support the importance of host-targeted interventions to reduce pathogen transmission and human disease risk.

Ectotherms such as the tiger mosquito, Aedes albopictus (Skuse), are particularly sensitive to increasing temperatures due to climate change. While previous research has shown how Ae. albopictus is impacted by higher constant temperatures, less is known about how this species will respond to heatwaves-short time periods with maximum temperatures above normal. Due to mosquitoes' short generation time, heatwaves may occur during only one life stage, each of which differs in habitat, morphology, and thermal tolerance. In this study, we exposed mosquitoes to a five-day heatwave in the lab at the egg, larval, or adult stage and measured development and survival. Additionally, we had one group undergo heatwave conditions throughout all life stages to distinguish the effects of prolonged heat exposure and short-term, stage-specific heatwaves. We found that constant heatwave exposure reduced hatching success and delayed hatching in surviving eggs after the initial five-day treatment, increased female development rate, and decreased pupal and adult survival compared to controls. However, heatwaves at a single life stage did not significantly alter development rates or survival apart from adult survival, which was reduced. Our results suggest that while the juvenile stages of Ae. albopictus show resilience to short, stage-specific heatwaves, longer heatwaves occurring across multiple stages can significantly reduce survival, with implications for population dynamics under future climate scenarios. This is particularly important due to the ability of Ae. albopictus to vector many viruses including chikungunya and dengue.

Bloodfed mosquitoes provide direct evidence of host use, a critical factor for understanding and managing mosquito-borne diseases, yet they are difficult to collect. This study assessed 6 bloodfed mosquito collection methods: direct aspiration, 2 commercially available surveillance traps, and 3 types of artificial resting shelters (ARS) at commercial piggeries and in nearby wetlands within Australia. Methods were evaluated for collection success (ability to capture bloodfed mosquitoes in field conditions) and efficiency (bloodfed mosquitoes collected per minute of effort), while also evaluating the influence of temperature, precipitation, and water index on trapping outcomes using a generalized linear mixed model. Of the 2,530 bloodfed mosquitoes collected, aspiration achieved the highest overall success, largely due to 2 exceptionally productive sites. Two ARS (large bins and felt bags), however, performed more consistently across locations and were particularly efficient in locations with fewer bloodfed mosquitoes. Collection method strongly influenced species composition: aspiration and ground-level ARS collected primarily Culex annulirostris Skuse (Diptera: Culicidae), whereas felt-bag ARS suspended from trees captured proportionally more Anopheles annulipes Walker (Diptera: Culicidae). Aspiration and ARS were most effective near dense, humid ground vegetation: habitats that concentrate resting mosquitoes. These findings suggest a 2-step approach to optimize collection outcomes. First, identify natural resting locations, then match the collection to local abundance and target species: aspiration for ground vegetation with abundant Culex species, ARS (especially felt bags) for low-abundance or arboreal-resting species. This framework supports more targeted and efficient surveillance of mosquito feeding patterns.

The common bed bug, Cimex lectularius L. (Hemiptera: Cimicidae), is an obligately hematophagous insect with a broad host range including humans, bats, and chickens. There are significant interspecific and intraspecific differences in hematological parameters of these hosts, yet little is known about their effects on life history traits of bed bugs. In this study, we investigate the hematocrit, or red blood cell concentration, and its effects on bed bug fitness. We conducted dose-response experiments using human blood of different hematocrits, and assessed development time, feeding rate, adult body size, egg production, and egg hatch rate. Human blood with hematocrits ranging from 35% to 50% equally supported nymphal development. However, feeding bed bug nymphs a hematocrit of 60% resulted in high mortality (78%), low feeding rate, and none of the bed bug nymphs reached the adult stage. Additionally, bed bugs fed human blood with a 20% hematocrit emerged as significantly smaller adults. These results suggest a nutritional deficiency at low (∼20%) hematocrits and toxicity at high hematocrits (∼60%). In our assessment of fecundity, we observed maximal egg production at 35-50% hematocrit and deficiencies in egg production at low (20-30%) and high (60%) hematocrits. We conclude that bed bugs are well adapted to feed on a broad range of human blood hematocrits and hypothesize that this tolerance may allow them to thrive on alternative hosts. Considering the detrimental effects of very low and high hematocrits, studies that rely on laboratory rearing of hematophagous arthropods should consider hematological parameters during experimental design.