In Africa,
An. funestus plays a major role in malaria transmission in several areas [
31,
32]. The
An. funestus group is composed of many species, which can be differentiated only from discrete traits of both larvae and adults [
33]; specific PCR has been developed to differentiate the species in the group [
30]. Nine species have been described, with widely different biology and vectorial capacity. Apart from
An. funestus, the other species appear to be mainly zoophilic [
34]. Human
Plasmodium has been found mainly in
An. funestus, which is an excellent vector, with high vectorial capacity, and only rarely in
Anopheles rivulorum[
35].
Anopheles vaneedeni has been experimentally infested [
36].
Anopheles funestus is a major vector of malaria transmission in Dielmo [
23,
37]. The studies in the 1990s showed entomological inoculation rates that reached up 180 infected bites per person per year. In contrast, after introduction of LLINs,
An. funestus almost completely disappeared, and the annual aggressiveness dropped from 17.2 bites per person per night to fewer than 1.2 (unpublished data). This may be due to the susceptibility of
An. funestus to insecticides, an ineffective sampling method to estimate human exposure to mosquito bites or a behavioural change to avoid intra-domicilary control. In Africa, resistance of
An. funestus to insecticides is widespread, although no
kdr alleles has been found; nevertheless, the presence of biochemical resistance of this species to all classes of insecticide, pyrethroids, carbamates and DDT, has been demonstrated [
38,
39]. This phenomenon has not been seen in the village of Dielmo (unpublished data). However, inadequate capture methods may be the reason why this vector is not encountered. In a recent study in Zambia [
40], it was observed that an Ifakara Tent Trap (model-C) placed outdoors was thirty four times more sensitive than HLC for sampling
An. funestus after deployment of LLINs. In the case of
An. funestus behavioural change, many studies have shown that new mosquito behaviour is an adaptive response to control strategies. Indeed the excito-repellents effects of treated bed nets repel mosquitoes outdoor, it follow a behavioural change strategy which is marked by changes in the biting time and place if the vector is highly endophilic and sometimes shift in host feeding [
16]. In the current study, diurnal activity was seen in
An. funestus, with a peak of aggressiveness between 08:00 and 9:00. These results are similar to those of studies in southern Benin after scaling up of universal coverage with LLINs, where 26.4% of
An. funestus were caught after 06:00 [
22]. The authors concluded that this vector has exophilic behaviour, because the villagers wake up early to work on crops. Exophilic behaviour was also reported in Tanzania by Russel
et al. [
13] after massive deployment of LLINs, although early biting activity of
An. funestus was demonstrated. The authors showed that this behavioural change in
An. funestus was responsible for residual outdoor transmission of malaria. Previous studies reported that behavioural changes to others
Anopheles vectors. In Dielmo, Trape
et al.[
10] reported an early biting of
An. gambiae after prolonged use of LLINs and in Benin Corbel
et al.[
11] showed greater exophagy rates of
An. gambiae and
An. funestus was recorded with a massive presence coupled with a shift from endophagic to exophagic behaviour. Another sibling species of
An. gambiae,
Anopheles arabiensis showed early biting activities in Ethiopia after use of LLINs both indoors and outdoors; and 80 per cent of this vector were captured before 22:00 with a peak activity between 19:00 to 20:00 [
17]. All these studies showed the emergence of the behavioural adaptation of mosquitoes in response to indoor interventions, which can thus jeopardize the efficacy of these tools and also constitute a risk to people who are so accessible.
In the present study, one mosquito was found infected, which was captured during the day, while since distribution of impregnated nets in this village, no
An. funestus had been found positive by ELISA. This constitutes a real risk for malaria transmission in this locality. The new phenotypes of mosquito have a human blood index and high parity, showing that a close relationship has been maintained between
Anopheles and humans, despite the distribution of LLINs. The concept of phenotypic plasticity or the selection of specific genetic traits for adapting to environmental conditions appears to confirm Pates
et al. [
21]. This behavioural change represents a characteristic to respond to new environmental conditions represented by the use of LLINs. Russell
et al.[
41] showed in Tanzania that
An. funestus was strongly exophilic and made a trophic deviation to cattle after universal coverage with LLINs, while in Benin [
22] and Senegal, an exceptional, remarkable adaptation has been seen. The fundamental concept of biology appears to be respected: in the face of stressful situations, organisms adapt or disappear [
42].