Abstract
BackgroundMembers of the Anopheles hyrcanus group have been incriminated as important malaria vectors. This study aims to identify the species and explore the insecticide susceptibility profile within the Anopheles hyrcanus group in Ubon Ratchathani Province, northeastern Thailand where increasing numbers of malaria cases were reported in 2014.MethodsBetween 2013 and 2015, five rounds of mosquito collections were conducted using human landing and cattle bait techniques during both the rainy and dry seasons. Anopheles mosquitoes were morphologically identified and their insecticide susceptibility status was investigated. Synergist bioassays were carried out with An. hyrcanus (s.l.) due to their resistance to all insecticides. An ITS2-PCR assay was conducted to identify to species the Hyrcanus group specimens.ResultsOut of 10,361 Anopheles females collected, representing 18 taxa in 2 subgenera, 71.8% were morphologically identified as belonging to the Hyrcanus Group (subgenus Anopheles), followed by An. barbirostris group (7.9%), An. nivipes (6.5%), An. philippinensis (5.9%) and the other 14 Anopheles species. Specimens of the Hyrcanus Group were more prevalent during the rainy season and were found to be highly zoophilic. Anopheles hyrcanus (s.l.) was active throughout the night, with an early peak of activity between 18:00 h and 21:00 h. ITS2-PCR assay conducted on 603 DNA samples from specimens within the Hyrcanus Group showed the presence of five sisters species. Anopheles peditaeniatus was the most abundant species (90.5%, n = 546), followed by An. nitidus (4.5%, n = 27), An. nigerrimus (4.3%, n = 26), An. argyropus (0.5%, n = 3), and An. sinensis (0.2%, n = 1). All An. hyrcanus (s.l.) specimens that were found resistant to insecticides (deltamethrin 0.05%, permethrin 0.75% and DDT 4% and synergist tests) belonged to An. peditaeniatus. The degree of resistance in An. peditaeniatus to each of these three insecticides was approximately 50%. Addition of PBO (Piperonyl butoxide), but not DEF (S.S.S-tributyl phosphotritioate), seemed to restore susceptibility, indicating a potential role of oxidases as a detoxifying enzyme resistance mechanism.ConclusionsA better understanding of mosquito diversity related to host preference, biting activity and insecticide resistance status will facilitate the implementation of locally adapted vector control strategies.
Highlights
Members of the Anopheles hyrcanus group have been incriminated as important malaria vectors
Several species of this group have previously been identified as active malaria vectors transmitting Plasmodium vivax, as well as lymphatic filariasis caused by Brugia malayi and Wuchereria bancrofti in many countries of South, Southeast and East Asian regions [3, 4]
Our findings showed that An. hyrcanus group was the most represented taxon with a total of 7442 specimens corresponding to 72.5% of the total Anopheles population
Summary
Members of the Anopheles hyrcanus group have been incriminated as important malaria vectors. In the southern Palearctic and Oriental regions, the Hyrcanus Group of mosquitoes is a complex species assemblage belonging to the Myzorhynchus Series of the subgenus Anopheles (Diptera: Culicidae), which comprises 26 closely related species [1, 2]. Several species of this group have previously been identified as active malaria vectors transmitting Plasmodium vivax, as well as lymphatic filariasis caused by Brugia malayi and Wuchereria bancrofti in many countries of South, Southeast and East Asian regions [3, 4]. The species of the Hyrcanus Group are considered as economic pests of cattle due to their vicious biting behavior and ability to transmit cervid filariae of the genus Setaria [21, 22]
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