Resistance Status of Anopheles maculipennis and Anopheles superpictus to the Conventional Insecticides in Northeastern Caspian Littoral, Iran

Background: Malaria resurgence has occurred in the northern half parts of Iran. The resurgence of malaria in the prone area could arise from various factors, e.g. wide use of pesticides in the agriculture sector and factors such as habitual patterns of movement of local people from problematic southeastern foci in Iran toward the Caspian Littoral. There are no new data on the re­sistance status of main malaria vectors in the Caspian Littoral, and this study was aimed at renewal data on conventional insecticides. Methods: The field strain of adult Anopheles superpictus and Anopheles maculipennis were collected using the hand catch method and transferred to the laboratory. The susceptibility tests were carried out against DDT 4%, Malathion 5%, Permethrin 0.75%, Deltamethrin 0.05%, and Lambda-cyhalothrin 0.05%, followed by the WHO’s procedure. Results: The primary malaria vector in Caspian Littoral is An. maculipennis, revealed to be still resistant to DDT and mortali­ty rate, LT50 and LT90 of female mosquitoes were 75.0%, 54.2, minutes and 111.3 minutes. The under ’verifica­tion re­quired’ status of An. maculipennis was also revealed to Lambda-cyhalothrin based on recent WHO’s criteria. The ma­laria vector An. superpictus is also considered the second malaria vectors in the west parts of the studied area, which showed to be susceptible to all insecticides tested. Conclusion: DDT resistance is persisted in An. maculipennis despite stopping residual spraying with DDT since 1978 in the Caspian Littoral, but the occurrence of pyrethroid under ’verification required’ status is a progressive threat to the possible development of cross-resistance in the future.

Investigation of DDT resistance mechanisms in Anopheles funestus populations from northern and southern Benin reveals a key role of the GSTe2 gene

Background Understanding the molecular basis of insecticide resistance in mosquito, such as Anopheles funestus, is an important step in developing strategies to mitigate the resistance problem. This study aims to assess the role of the GSTe2 gene in DDT resistance and determine the genetic diversity of this gene in An. funestus. Methods Gene expression analysis was performed using microarrays and PCR while the potential mutation associated with resistance was determined using sequencing. Results Low expression level of GSTe2 gene was recorded in Burkina-Faso samples with a fold change of 3.3 while high expression (FC 35.6) was recorded in southern Benin in Pahou (FC 35.6) and Kpome (FC 13.3). The sequencing of GSTe2 gene in six localities showed that L119F-GSTe2 mutation is almost getting fixed in highly DDT-resistant Benin (Pahou, Kpome, Doukonta) and Nigeria (Akaka Remo) mosquitoes with a low mutation rate observed in Tanongou (Benin) and Burkina-Faso mosquitoes. Conclusion This study shows the key role of the GSTe2 gene in DDT resistant An. funestus in Benin. Polymorphism analysis of this gene across Benin revealed possible barriers to gene flow, which could impact the design and implementation of resistance management strategies in the country.

Detection and functional characterization of sigma class GST in Phlebotomus argentipes and its role in stress tolerance and DDT resistance

Several Glutathione S-transferases (GSTs) enzymes, in insects, have previously been implicated in resistance developed against DDT and other insecticides. The GST enzyme particularly sigma class have important physiological role in detoxification of lipid peroxidation by-products in insects. Phlebotomus argentipes has been intensely exposed to DDT over years due to Indoor Residual Spray (IRS) programme for Kala-azar elimination in Bihar, India. However, in P. argentipes, role of GSTs in DDT resistance have not been elucidated. Here, sigma class GST of P. argentipes (Parg-GSTσ) was successfully cloned, expressed and purified by affinity chromatography. The recombinant Parg-GSTσ was found to be highly active towards cumene hydroperoxide and 4-HNE having specific activity 92.47 & 203.92 µM/min/mg of protein, respectively and exhibited low activity towards universal substrate CDNB i.e., 8.75 µM/min/mg of protein. RT-PCR and immunoblot analysis showed at least 2 and 1.8 fold overexpression of Parg-GSTσ in the single exposed and non exposed DDT resistant P. argentipes as compared to susceptible, implicating Parg-GSTσ also involved in DDT resistance probably by imparting enhanced stress tolerance. The DDT, H2O2 and temperature induction assays demonstrated stress-dependent induction of Parg-GSTσ expression indicating its important role in oxidative stress redressal.