Variations in susceptibility to common insecticides and resistance mechanisms among morphologically identified sibling species of the malaria vector Anopheles subpictus in Sri Lanka

Abstract

BackgroundAnopheles subpictus s.l., an important malaria vector in Sri Lanka, is a complex of four morphologically identified sibling species A-D. Species A-D reportedly differ in bio-ecological traits that are important for vector control. We investigated possible variations that had not been reported previously, in the susceptibility to common insecticides and resistance mechanisms among the An. subpictus sibling species.MethodsAdult An. subpictus were collected from localities in four administrative districts in the dry zone of Sri Lanka. Single female isoprogeny lines were established and sibling species status determined according to reported egg morphology. World Health Organization's standard protocols were used for insecticide bioassays and biochemical assays to determine insecticide susceptibility and resistance mechanisms. Susceptibility of mosquitoes was tested against DDT (5%), malathion (4%), deltamethrin (0.05%) and λ-cyhalothrin (0.05%). Biochemical basis for resistance was determined through assaying for esterase, glutathione-S-transferase and monooxygenase activities and the insensitivity of acetycholinesterase (AChE) to propoxur inhibition.ResultsAll sibling species were highly resistant to DDT. However there were significant differences among the sibling species in their susceptibility to the other tested insecticides. Few species A could be collected for testing, and where testing was possible, species A tended to behave more similarly to species C and D than to B. Species B was more susceptible to all the tested insecticides than the other sibling species. This difference may be attributed to the predominance of species B in coastal areas where selection pressure due to indoor residual spraying of insecticides (IRS) was lower. However there were significant differences between the more inland species C and D mainly towards pyrethroids. Higher GST activities in species C and D might have contributed to their greater DDT resistance than species B. Malathion resistance in both species C and D may be caused by elevated GST activity and an altered insensitive target site in AChE. In addition, a carboxylesterase based malathion resistance mechanisms was also detected in species C and D. Elevated esterase levels in species C and D might have contributed to the low levels of pyrethroid resistance. However an absence of elevated activity of monooxygenases in species B, C and D indicates that monooxygenases are unlikely to be the cause of this partial resistance to pyrethroids.ConclusionsThe differences in insecticide susceptibility and insecticide resistance mechanism shown by An. subpictus sibling species are important considerations for developing the malaria control and eradication program in Sri Lanka. Similar studies on species complexes of other anopheline vectors of malaria are necessary for effective malaria control worldwide. The differential susceptibility findings are also consistent with most, if not all, morphologically identified An. subpictus species B in Sri Lanka belonging to the An. ...

Molecular characterization and identification of members of the Anopheles subpictus complex in Sri Lanka

“…However, species B in Sri Lanka can breed in both fresh and brackish water with salinity ranging from 0–30 ppt [11]. In addition, the predominantly inland species (morphologically identified as C and D and inferred from molecular data herein to be species A) are more resistant to common insecticides than the coastal population of species B [12]. This differential adaptation is likely caused by higher selection pressure on species A as decades of insecticide application to control malaria and for use in agriculture has mainly targeted the freshwater-inland areas in Sri Lanka.…”

“…Like any species complex, members of the Subpictus complex show differential bio-ecological traits such as salinity tolerance, susceptibility to common insecticides and vectorial capacity [5,7,11,12]. The development of appropriate vector control strategies when dealing with species complexes, therefore, requires reliable molecular diagnostic tools and an understanding of inter and intraspecific genetic diversity of vector populations [13].…”

“…In India, species B is predominant and is a vector in coastal areas of Southern India whereas species A, C and D are predominant in inland areas [1,7] with species A being a vector in West Bengal of India [14]. The members of the Subpictus complex in Sri Lanka also differ in bio-ecological properties [9,11,12] but the full characterization of these requires the development of reliable species diagnostic tools.…”

First Report on Adulticide Susceptibility Status of Aedes albopictus, Culex quinquefasciatus, and Culex vishnui from a Pig Farm in Tanjung Sepat, Selangor, Malaysia

“…Different activity behaviors (i.e., biting and resting behaviors), habitats, as well as environmental conditions, may allow the mosquitoes to be exposed to different insecticide treatments and consequently resulting in varied susceptibility (Liu et al 2004, Surendran et al 2012. albopictus, Cx.…”

Characterization of metabolic detoxifying enzymes in an insecticide resistant strain of <i>Aedes aegypti</i> harboring homozygous S989P and V1016G <i>kdr</i> mutations

“…Homogenates were centrifuged at 10,000×g for 20 minutes at 4°C, and supernatants were transferred to fresh microcentrifuge tubes. The protocol for esterase assay followed Surendran et al (2012). p-Nitrophenyl acetate (pNPA) (SigmaAldrich) was used as a substrate.…”