Biting patterns and host preference of Anopheles epiroticus in Chang Island, Trat Province, Eastern Thailand

A study of species diversity of Anopheles mosquitoes, biting patterns, and seasonal abundance of important mosquito vectors was conducted in two villages of Chang Island, Trat Province, in eastern Thailand, one located along the coast and the other in the low hills of the central interior of the island. Of 5,399 captured female anophelines, 70.25% belong to the subgenus Cellia and remaining specimens to the subgenus Anopheles. Five important putative malaria vectors were molecularly identified, including Anopheles epiroticus, Anopheles dirus, Anopheles sawadwongporni, Anopheles maculatus, and Anopheles minimus. Anopheles epiroticus was the most commonly collected species in the coastal site, whereas An. dirus was found to be most abundant in the forest-hill site. From both locations, a greater number of mosquitoes was collected during the dry season compared to the wet. Anopheles epiroticus showed greater exophagic and zoophilic behavior with the highest blood feeding densities occurring between 18:00 and 19:00. In contrast, An. dirus demonstrated an activity peak between midnight and 01:00. We conclude that An. epiroticus and An. dirus, in coastal and inland areas, respectively, appear to be the most epidemiologically important malaria vectors on Chang Island. As no studies of vector competency specific to Chang Island have been conducted, our conclusions that these two species play a primary role in malaria transmission are based on evidence from other localities in Thailand and mainland Southeast Asia. This information serves as a basis for designing improved vector control programs that target specific species, and if integrated with other interventions could result in the elimination of malaria transmission on the island

Diversity of Anopheles species and trophic behavior of putative malaria vectors in two malaria endemic areas of northwestern Thailand

We determined the species diversity, blood-feeding behavior, and host preference of Anopheles mosquitoes in two malaria endemic areas of Tak (Mae Sot District) and Mae Hong Son (Sop Moei District) Provinces, located along the Thai border with Myanmar, during a consecutive two-year period. Anopheline mosquitoes were collected using indoor and outdoor human-landing captures and outdoor cow-baited collections. Mosquitoes were initially identified using morphological characters, followed by the appropriate multiplex AS-PCR assay for the identification of sibling species within Anopheles (Cellia) complexes and groups present. Real-time PCR was performed for parasite-specific detection in mosquitoes (Plasmodium spp. and Wuchereria bancrofti). A total of 7,129 Anopheles females were captured, 3,939 from Mae Sot and 3,190 from Sop Moei, with 58.6% and 37% of all anophelines identified as An. minimus, respectively. All three malaria vector complexes were detected in both areas. One species within the Minimus Complex (An. minimus) was present along with two related species in the Funestus Group, (An. aconitus, An. varuna), two species within the Dirus Complex (An. dirus, An. baimaii), and four species within the Maculatus Group (An. maculatus, An. sawadwongporni, An. pseudowillmori, and An. dravidicus). The trophic behavior of An. minimus, An. dirus, An. baimaii, An. maculatus, and An. sawadwongporni are described herein. The highest An. minimus densities were detected from February through April of both years. One specimen of An. minimus from Mae Sot was found positive for Plasmodium vivax

Genetic Diversity and Gene Flow among Stable Fly Populations, Stomoxys calcitrans (L.) in Thailand

ABSTRACT Isozymes from five wild-caught Stomoxys calcitrans (L.) were compared using starch gel electrophoresis to estimate the rates of gene flow between and among S. calcitrans populations from five different geographic regions of Thailand. Among ten enzyme systems, 13 putative loci and 10 polymorphisms were detected. Limited genetic differentiation among the five populations was observed as indicated by the low F ST (0.078). The highest percentage of polymorphic loci was observed in eastern Trat province and northern Chiang Mai province (69.2%), whereas the lowest percent polymorphism was seen in south-central Saraburi province (23.1%). Gene flow between populations varied from 6.16 to 15.38 reproductive migrants per generation with no fixed genetic differences detected. Among the five population samples, no correlation was seen between genetic and geographical distances showing that sampled S. calcitrans fit closely in the same cluster taxa. The genetic and epidemiological ramifications of these findings are discussed

Diversity of Anopheles species and trophic behavior of putative malaria vectors in two malaria endemic areas of northwestern Thailand

ABSTRACT: We determined the species diversity, blood-feeding behavior, and host preference of Anopheles mosquitoes in two malaria endemic areas of Tak (Mae Sot District) and Mae Hong Son (Sop Moei District) Provinces, located along the Thai border with Myanmar, during a consecutive two-year period. Anopheline mosquitoes were collected using indoor and outdoor human-landing captures and outdoor cow-baited collections. Mosquitoes were initially identified using morphological characters, followed by the appropriate multiplex AS-PCR assay for the identification of sibling species within Anopheles (Cellia) complexes and groups present. Real-time PCR was performed for parasite-specific detection in mosquitoes (Plasmodium spp. and Wuchereria bancrofti)

Pyrethroid Susceptibility in <i>Stomoxys calcitrans</i> and <i>Stomoxys indicus</i> (Diptera: Muscidae) Collected from Cattle Farms in Southern Thailand

The susceptibility to six pyrethroid insecticides (permethrin, deltamethrin, alpha-cypermethrin, cypermethrin, lambda-cyhalothrin, and bifenthrin), each at the recommended concentration, was evaluated for two stable fly species—Stomoxys calcitrans (Linnaeus, 1758) and Stomoxys indicus Picard, 1908 (Diptera: Muscidae)—through tarsal contact using a World Health Organization (WHO) cone bioassay procedure. The field populations of S. calcitrans were collected from the Songkhla and Phattalung provinces, while S. indicus were collected from the Phattalung and Satun provinces in Thailand. The stable flies were exposed to insecticide-treated filter paper for 30 min, and their knockdown counts at 30 min and 60 min and mortality counts at 12 h and 24 h were recorded. The S. calcitrans and S. indicus Songkhla and Phattalung populations were moderately susceptible to pyrethroids, as indicated by the 24 h mortality. Nonetheless, the Satun population of S. indicus was completely susceptible to permethrin, with 100% mortality, and showed the lowest susceptibility to deltamethrin and bifenthrin. The results indicate the generally low susceptibility of stable flies to pyrethroids in the southern provinces of Thailand

Phenotypic susceptibility to pyrethroids and organophosphate of wild Stomoxys calcitrans (Diptera: Muscidae) populations in southwestern France.

International audienceStomoxys calcitrans (Diptera: Muscidae), is an important vector of lumpy skin disease and bovine besnoitiosis in Europe. Control of this biting fly could represent a keystone in the containment of this emerging disease. Reports of insecticide resistance in S. calcitrans are scarce in Europe. Therefore, the purpose of this study was to evaluate the phenotypic susceptibility to deltamethrin, cypermethrin and phoxim of five wild S. calcitrans populations from southwestern France, where transmission of bovine besnoitiosis is very prevalent. Adult S. calcitrans were caught at each study site and exposed to insecticide-impregnated filter papers under laboratory conditions. Quantities of active ingredients on filter papers corresponded to the recommended doses proposed by the manufacturers (37.5 mg a.i./m2 of cattle's skin, 125 mg a.i./m2 and 750 mg a.i./m2 for deltamethrin, cypermethrin and phoxim respectively) were tested. Knock-down effects (KD) (1 h after the onset of exposure) and mortality rates (24 h and 48 h after exposure) were evaluated. Phoxim showed a rapid and full efficacy in all populations. However, the KD effects (37.5 to 97.5%) and the mortality rates at 48 h (10 to 91.25%) induced by the exposure to pyrethroids varied greatly according to the study site but none of the populations showed full susceptibility. Therefore, the current recommended doses of these pyrethroids are probably less efficient than expected in the field and should be considered with caution in the control of bovine besnoitiosis in France

Anopheles species diversity and distribution of the malaria vectors of Thailand

In Thailand, seven Anopheles species within three species assemblages have been incriminated as important malaria vectors. Comprehensive maps showing the countrywide geographical distribution of primary and secondary malaria vector species have not yet been developed; the maps that do exist are typically restricted to specific areas or are out of date. In addition, with the advent of molecular-based species-identification tools, the geographical locations of various sibling species have been more clearly defined in the country. This review has compiled published data on the known distribution of important malaria vectors in Thailand based on genetic and molecular identification assays from 1994 to 2014, with maps of relevant species distribution provided herein