Mosquito species composition
A total of 2258 female specimens of An. gambiae s.l. were collected over the study period, 1988 by PSC and 270 mosquitoes by EWT. An. gambiae s.l. was the only malaria vector collected in both areas.
Molecular species composition of An. gambiae s.l.
An, gambiae s.l. consisted of three species: An. coluzzii, An. arabiensis and An. gambiae s.s. An. coluzzii was by far the most frequent species in both the IRS (96%, n = 97) and the no-IRS (95%, n = 430) areas (Figure 3).
Density of Anopheles gambiae s.l. per room
An. gambiae s.l. density increased with rainfall in the no-IRS area, while it remained low regardless of the variations in rainfall in the IRS area (Figure 4). The highest density was observed in July and August in the no-IRS area. In the IRS area, two small peaks were observed: one in July (just before the IRS implementation), and one in September (two months after the IRS). There was a strong correlation between rainfall and An. gambiae s.l. density, with 1-month lag, and rainfall in both the IRS (R = 0.888, P = 0.018) and the no-IRS (R = 0.806, P = 0.053) areas.
Parity rate of Anopheles gambiae s.l.
The parity rate were estimated form samples collected by EWTs. The average parity rates were 96.42% (N= 56) and 98.36% (N= 122) in the IRS and no-IRS areas, respectively. There was no statistical significant difference (P>0.05) between the parity rates in the two zones.
Human biting rate of Anopheles gambiae s.l.
Using PSC, the overall mean monthly human biting rates (MHBRs) of An. gambiae s.l. were higher in the no-IRS area (20.41 bites/person/month) than in the IRS area (3.03 bites/person/month). In the IRS area, the peak of the MHBR (7.47 bites/person/month) was observed in September (> 2 months after IRS). In the no-IRS area it was observed in August (66 bites/persons/month). In both areas, the lowest MHBR was observed in June (Figure 5).
Infection rate and Entomological inoculation rates (EIR) in An. gambiae s.l.
The infection rate was obtained from pool sample of PSC and EWTs. The mean P. falciparum infection rate of An. gambiae s.l. over the study period in the no-IRS area was 1% (n = 1670). In the IRS area, the number of An. gambiae s.l. specimens collected and tested (n = 253) by ELISA did not allow us to detect an infection (Figure 6). In the no-IRS area, the overall mean EIR was 0.21 infective bites/person/month peaking in September with 0.75 infective bites per person per month (Figure 6).
Human blood index
The HBI (PSC) shows that the mosquitoes were highly anthropophilic in both areas. The average HBI in the IRS area was 74.27% (n=171) and 86.90% (n=1199) in the no-IRS area. However, monthly variations in this rate were observed in both areas. The highest HBIs were recorded in October in the IRS area (98%) and in August in the no-IRS area (89%). The HBI was higher in the no-IRS area compared to those in the IRS area (χ2 = 19.84; P < 0.001).
Resistance of An. gambiae s.l. to insecticides
Bioassays tests were carried out on adult females emerged from larvae collected in the different field sites (F0). Results showed high resistance to the deltamethrin in the four study sites (Figure 6) with mortality rates of 15%, 20%, 24.5% and 41% respectively in Karadié (N= 100), N'Galamadibi (N= 150), Kolondialan (N= 150) and Koula (N= 200). An. gambiae s.l. was resistant to the bendiocarb (Figure 6) in all study sites with mortality rates of 56%, 73%, 79%, 69% respectively in Koula (N=150), Karadié (N=100), N'Galamadibi (N=200) and Kolondialan (N=200). Susceptibility to pirimiphos-methyl was observed in all study sites.