Malaria remains the most severe infectious disease and a major public health challenge in Nigeria [
1,
2]. It is the main cause of morbidity and mortality in this most populous Africa country, with 97% of the national population at risk: it is responsible for an estimated 300,000 deaths annually in Nigeria; and it contributes to an estimated 11% maternal mortality as well as 25% of infant mortality [
1,
3]. Malaria transmission in Nigeria has been attributed mainly to
Anopheles gambiae sensu stricto (
s.s.) and
Anopheles funestus s.s. [
4‐
6] with consistent
Plasmodium infection rates of 1.0–2.7% (
An. funestus) and 3.0–8.1% (
An. gambiae) previously reported in case studies in Ogun, Oyo and Lagos states [
4,
5]. Although, there was also a high sporozoite infection rate of 25% reported in Lagos state [
7]. In Nigeria, malaria control relies hugely on the use of indoor residual spraying (IRS) and insecticide-treated nets (ITNs) [
2,
3]. However, resistance against the main insecticides used in public health (pyrethroids, carbamates and organochlorines) in malaria vectors is threatening the effectiveness of these control tools.
Anopheles gambiae s.s resistance to insecticides, notably against pyrethroids [
8], DDT [
9,
10] and bendiocarb [
11], has been documented in Nigeria, however, little is known so far concerning the insecticide susceptibility of the other major malaria vector
An. funestus s.s. in the country. Pyrethroid insecticide is the class of insecticide mainly used in Nigeria for both ITNs and IRS [
2]. Two types of pyrethroids are mainly used in Nigeria for insecticide nets treatment: permethrin (Type 1) and deltamethrin (Type 2). In recent years,
An. funestus s.s. populations have increasingly been reported to be resistant to these insecticides in other African countries, such as Uganda in East Africa [
12]; Mozambique, Zambia, Zimbabwe and Malawi in Southern Africa [
13‐
19], Cameroon in Central Africa [
20,
21] and some West African countries, including Benin [
22], Ghana [
23] and Burkina-Faso [
24]. Resistance patterns against these insecticides vary significantly across Africa. For example,
An. funestus was resistant to pyrethroids and carbamate but fully susceptible to DDT and dieldrin in southern Africa [
20,
25]. However, a recent study in Malawi showed that this mosquito species has now began to develop resistance against organochlorines (dieldrin and DDT) [
17].
Anopheles funestus is resistant to pyrethroids and DDT, but remains susceptible to carbamate in Uganda and western Kenya [
12]. High resistance profiles were recorded with dieldrin in Cameroon [
20]. In the neighbouring country of Benin, resistance firstly reported in 2011 [
22] from the coast (Pahou) and was recently shown to have extended to the inland as the Kpome population was shown to be resistant to all insecticide classes apart from organophosphates [
26]. It remains to be established whether these resistances are also present in Nigeria and if yes information on the resistance pattern will be useful for the malaria control programs especially on the suitable insecticides to use for the control of this species.
Metabolic resistance mechanisms have so far been implicated in insecticide-resistant
An. funestus across Africa [
12,
22,
27] with cytochrome P450 genes conferring pyrethroid resistance and also cross-resistance to carbamates in southern African [
28] as previously reported also for
An. gambiae [
29]. DDT resistance mechanisms in
An. funestus on the other hand have been associated with an up-regulation of glutathione S-transferases notably
GSTe2 coupled with a point mutation L119F [
27]. No L1014F-kdr mutation has been implicated in pyrethroids and DDT resistance [
12,
22], and no association exists between G119S and F455W mutations of the
Ace-
1 gene and carbamate resistance in this mosquito species [
12,
22,
25]. However, the recent discovery of a new
Ace-
1 mutation (N485I) associated with carbamate resistance in southern African
An. funestus populations [
28] coupled with the presence of the A296S-RDL mutation in the GABA receptor of
An. funestus [
20] are evidence that target-site resistance mechanism also play a role in insecticide resistance profiles recorded in this malaria vector.
In order to help malaria control programmes, to design evidence-based strategies to control An. funestus in Nigeria, and to manage potential existing resistance, this study aims to establish the insecticides susceptibility profile and investigate the molecular basis of resistance of this species population in Akaka Remo: a farm settlement in southwest Nigeria.