Malaria is vector-borne disease caused by five Plasmodium species namely; Plasmodium falciparum, P. ovale, P. malariae, P. vivax and P. knowlesi. The parasite transmitted to human through the bite of infective female Anopheles mosquito . There are over 445 recognized species of Anopheles mosquito of which around 70 species are potential malaria vectors . In Africa, the major malaria vectors are Anopheles gambiae and An. funestus species complexes, but there are also a number of primary and secondary vectors that contribute to the malaria transmission .
In Ethiopia, there are more than 45 documented Anopheles mosquito species , of which only four species are malaria vectors. Anopheles arabiensis, member species of the Anopheles gambiae complex, is the primary vector of malaria widely distributed in the country[4, 5]. Anopheles funestus An. pharoensis and An. nili are secondary vectors occurring with varying population densities, limited distribution and vector competence . Very recently, a new invasive Anopheles species, An. stephensi, has been documented in the country  which might complicate the malaria elimination effort of the country.
Chemical based vector control intervention is the pillar strategy to combat malaria. Indoor residual spraying (IRS) and long-lasting insecticidal nets (LLINs) are instrumental for the significant reduction of malaria morbidity and mortality . However, the emergence and widespread of insecticide resistance in the major malaria vectors particularly in Africa might compromise effectiveness of chemical based (IRS and LLINs) interventions against malaria control and elimination efforts [8–14].
Insecticide resistance has been reported in more than 500 insect species worldwide among which over 70 Anopheles species (Diptera: Culicidae) are responsible for the transmission of malaria parasites to humans (Hemingway and Hilary, 2000). Insecticide resistance has become a serious challenge for the control and elimination of malaria due to the fact that malaria vectors are resistant to the four commonly used insecticide classes (pyrethroids, organochlorines, carbamates and organophosphates) [8, 14]
In Ethiopia, DDT resistance by An. arabiensis was reported in the1990s, since then widespread DDT resistance documented throughout the country[9, 10, 16–18]. Moreover, resistance against other classes of insecticides such as carbamates (bendiocarb), organophosphates (malathion) and pyrethroids (permethrin, deltamethrin) has been reported from various regions of the country [18, 19]
In the last decade the number of malaria cases has declined due to a high coverage of IRS and scaling up of LLINs [8, 14]. This result initiated the national malaria control and elimination program of Ethiopia to develop national malaria elimination road map to eliminate malaria from the country by 2030 . However, this plan might be compromised as the magnitude of resistance against several insecticides is increasing in the An. arabiensis populations [8, 18, 19]
Insecticide resistance largely caused by two major mechanisms. The first one is due to target-site insensitivity as a result of mutations in the target site of the insecticide that changes binding. The second mechanism is metabolic based resistance, where the insecticide is either degraded, sequestered or transported/excreted out of the cell before binding to the target site [21, 22]
Target-site and metabolic based resistance mechanisms operating in malaria vectors in several malaria endemic African countries have been documented. Knockdown resistance (kdr) is target site mutations in the voltage-gated sodium channel gene of mosquito nerve membranes is associated with DDT and pyrethroids resistance. In Anopheles, this involves the substitution of leucine (TTA) to phenylalanine (TTT) (kdrL1014F) or to serine (TCA) (kdrL1014S) [23, 24]. In addition, substitution of asparagine to tyrosine (N1575Y) is linked with resistance in An. gambiae s.s  but not in An. arabiensis . There is also an acetylcholinesterase gene (ace-1R) mutation, substitution of glycine (GGC) to a serine (AGC) which confers resistance to organophosphates and carbamates . In Ethiopia, target site resistance mechanism, Kdr L1014F (West Africa Kdr), in populations of An. arabiensis documented in several populations across the country [9, 10, 16, 18, 19]
Metabolic based resistance in Anopheles mosquitoes have been reported from several countries in Africa [27–30]. Moreover, modifications in the cuticle either through cuticle thickening and/or altering of the cuticle composition of arthropods which can slow down the penetration of chemical compounds [31–33] has also been reported in Anopheles populations .
Approximately 60% of the Ethiopian populations live in malaria risk areas . The disease primarily occurs up to the 2000-meter (m) elevation but can also occasionally affect areas over 2000m elevation in response to the spatial and temporal changes [35, 36]. Malaria transmission is unstable and seasonal which produces little immunity in the community; hence malaria epidemics are common and lead to high mortality and morbidity . Gambella is one of the malarious areas of Ethiopia with high malarial endemicity. Itang special woreda is known for its a stable form of malaria transmission . Moreover, despite the current effort of the country malaria incidence rate in Itang did not decline unlike many other malarious areas of Ethiopia. . Moreover, to the best of our knowledge composition of mosquito fauna and insecticide resistance status of Anopheles gambiae s.l in Itang, not yet studied, and the resistance mechanisms operating in the populations not known. Therefore, this study aimed to investigate mosquito fauna composition, insecticide resistance status of Anopheles gambiae s.l and detection of target site mutations associated with DDT and pyrethroid resistance.