A total of 3,504 Anopheles mosquitoes that belongs to three species were collected: Anopheles gambiae s.l., Anopheles pharoensis, and Anopheles coustani cx. as morphologically identified. Anopheles gambiae s.l. accounted for 75.23% (n = 2,636, CI = 1.255–1.491, P = 0.000) of the total, while the Anopheles coustani cx. represented 9.25% (n = 324, CI = 0.322–0.134, P = 0.000). The highest number (59.80%, n = 2,098 CI = 1.682–1.968, P = 0.00) of Anopheles mosquitoes was collected using CDC LT which was followed by PSC, Pit shelter, and Handheld mouth Aspirator (N) collection methods. The least number of Anopheles mosquitoes was collected by Pit shelter/PIT 340 (n = 9.70%). Anopheles gambiae s.l. was the most abundant species trapped using all collection methods while Anopheles coustani cx. was the least in all collection tools (Table 1).
Hourly biting activities
Anopheles species had their highest biting activity between 6:00 PM and 10:00 PM both indoors and outdoors which was statistically significant compared to midnight and early morning biting hours (Mean = 0.26, CI = 0.21–0.31, p = 0.000). Anopheles gambiae s.l. had shown overnight biting pattern, with peak densities from 7:00 PM to 10:00 PM and 3:00 AM to 5:00 AM and the lowest biting activity between 11:00 PM and 2:00 AM, the variation was statistically significant (p- value = 0.000) detail presented in supplementary information (table SI 1). Anopheles pharoensis biting activity decreased sharply between 10:00 PM and 4:00 AM both indoor and outdoor (Fig. 1).
Figure 2 shows the night time activities of the householders. Most of them go to sleep at 11:00 PM, but some of them are still awake at 10:00 PM or 12:00 AM. The hourly biting density of Anopheles mosquitoes is positively correlated with the number of active householders before and after bedtime (r = 0.135, P = 0.00). On the other hand, the biting density is negatively correlated with the number of sleeping householders (Table 2). The regression analysis also shows that the activities of the householders before and after bedtime explain 2.8% of the variation in the biting density (R2 = 0.028, F = 16.78, P = 0.000). Moreover, the beta coefficients indicate that an increase in one active householder leads to a higher biting density of Anopheles mosquitoes (β = 0.038, t = 1.74, p = 0.08), while an increase in one sleeping householder leads to a lower biting density (β = -0.037, t= -1.7, p = 0.000).
Table 2
Correlation analysis of occupants’ activities and Anopheles mean density
Number of occupants | Mean ± SE | CI | Anopheles | CI | r | P |
Mean density of occupants on activities | 1.38 ± 0.05 | 1.29–1.47 | 0.06 ± 0.005 | 0.05–0.07 | 0.13 | 0 |
Mean density of occupants slept | 4.78 ± 0.04 | 4.69–4.86 | 0.02 ± 0.003 | 0.02–0.03 | -0.07 | 0.02 |
Mean density of occupants awake | 0.48 ± 0.02 | 0.44–0.53 | 0.04 ± 0.005 | 0.03–0.05 | 0.05 | 0.01 |
Anopheles species spatiotemporal dynamics
As determined by morphological identification, Anopheles gambiae s.l., Anopheles pharoensis and Anopheles coustani cx. were collected from Wonji Shoa and Bikiltu villages. Although greater number of Anopheles gambiae s.l., was collected from Wonji Shoa village, it was not different from that of Bikiltu villages (t = 0.81; P = 0.42) (Table 3). Similarly, there was no significant mean variation between the two study sites for the Anopheles pharoensis and Anopheles coustani cx. (t= -1.05; p = 0.08 and t = 1.06; p = 0.29, respectively).
Table 3
Anopheles species distribution in the study villages
Species | Study village | t-test | P- value |
Wonji Shoa | Bikiltu |
| Mean ± SE | Mean ± SE | | |
An. gambiae s.l. | 0.23 ± 0.01 | 0.22 ± 0.01 | 0.81 | 0.42 |
An. pharoensis | 0.06 ± 0.01 | 0.07 ± 0.01 | -1.05 | 0.08 |
An. coustani cx. | 0.04 ± 0.01 | 0.03 ± 0.00 | 1.06 | 0.29 |
Temporal dynamics of the mean density of Anopheles mosquito species in the Wonji Sugar Estate over 24 months of entomological monitoring is presented in Table 5. There were statistically significant monthly mean density differences among Anopheles gambiae s.l. (F = 17.71, P = 0.000), Anopheles pharoensis (F = 5.53, P = 0.000), and Anopheles coustani cx. (F = 10.85, P = 0.000). Anopheles gambiae s.l. outcompeted other species in both monthly abundance and availability; the difference was statistically significant at p = 0.000. The highest density of Anopheles species was noted in July 2019 followed by June 2019. Anopheles gambiae s.l. density was peaked in July 2019 while the least in December 2018. Higher mean densities of Anopheles pharoensis were noted in July 2019 and March 2019. The lowest density of was recorded through all the months, whilst non was collected in Anopheles coustani cx. was not collected in December 2018 and January 2019 (Table 4).
Table 4
Multiple comparisons of Anopheles species mean monthly density
Month & year | An. gambiae s.l. | An. pharoensis | An. Coustani cx. | Total |
| Mean ± SE | Mean ± SE | Mean ± SE | Mean ± SE |
Jul-18 | 0.236 ± 0.042 | 0.032 ± 0.014 | 0.008 ± 0.008 | 0.253 ± 0.043 |
Aug-18 | 0.186 ± 0.034 | 0.086 ± 0.021 | 0.004 ± 0.004 | 0.254 ± 0.037 |
Sep-18 | 0.302 ± 0.047 | 0.012 ± 0.028 | 0.004 ± 0.004 | 0.377 ± 0.048 |
Oct-18 | 0.191 ± 0.036 | 0.087 ± 0.025 | 0.015 ± 0.007 | 0.239 ± 0.041 |
Nov-18 | 0.185 ± 0.031 | 0.088 ± 0.021 | 0.004 ± 0.004 | 0.243 ± 0.035 |
Dec-18 | 0.047 ± 0.012 | 0.032 ± 0.011 | 0.000 ± 0.000 | 0.074 ± 0.017 |
Jan-19 | 0.057 ± 0.015 | 0.094 ± 0.019 | 0.000 ± 0.000 | 0.137 ± 0.024 |
Feb-19 | 0.053 ± 0.016 | 0.019 ± 0.011 | 0.01 ± 0.007 | 0.078 ± 0.020 |
Mar-19 | 0.112 ± 0.022 | 0.121 ± 0.025 | 0.057 ± 0.019 | 0.250 ± 0.033 |
Apr-19 | 0.1454 ± 0.027 | 0.086 ± 0.021 | 0.184 ± 0.036 | 0.350 ± 0.041 |
May-19 | 0.267 ± 0.031 | 0.033 ± 0.012 | 0.029 ± 0.012 | 0.308 ± 0.032 |
Jun-19 | 0.543 ± 0.043 | 0.104 ± 0.023 | 0.035 ± 0.016 | 0.600 ± 0.041 |
Jul-19 | 0.567 ± 0.047 | 0.168 ± 0.028 | 0.011 ± 0.006 | 0.627 ± 0.047 |
Aug-19 | 0.416 ± 0.045 | 0.038 ± 0.011 | 0.008 ± 0.005 | 0.432 ± 0.046 |
Sep-19 | 0.329 ± 0.040 | 0.102 ± 0.023 | 0.149 ± 0.029 | 0.411 ± 0.049 |
Oct-19 | 0.263 ± 0.032 | 0.104 ± 0.021 | 0.091 ± 0.024 | 0.380 ± 0.037 |
Nov-19 | 0.161 ± 0.026 | 0.046 ± 0.014 | 0.043 ± 0.016 | 0.226 ± 0.030 |
Dec-19 | 0.057 ± 0.015 | 0.011 ± 0.006 | 0.029 ± 0.011 | 0.088 ± 0.019 |
Jan-20 | 0.206 ± 0.028 | 0.044 ± 0.012 | 0.004 ± 0.004 | 0.237 ± 0.029 |
Feb-20 | 0.129 ± 0.019 | 0.029 ± 0.011 | 0.023 ± 0.010 | 0.175 ± 0.022 |
Mar-20 | 0.155 ± 0.026 | 0.027 ± 0.011 | 0.031 ± 0.013 | 0.194 ± 0.029 |
Apr-20 | 0.209 ± 0.033 | 0.023 ± 0.010 | 0.014 ± 0.008 | 0.222 ± 0.035 |
May-20 | 0.237 ± 0.036 | 0.021 ± 0.009 | 0.009 ± 0.007 | 0.355 ± 0.037 |
Jun-20 | 0.301 ± 0.044 | 0.046 ± 0.016 | 0.043 ± 0.016 | 0.346 ± 0.045 |
Total | 0.223 ± 0.007 | 0.065 ± 0.004 | 0.034 ± 0.003 | 0.282 ± 0.008 |
Mean square | 1.53 | 0.14 | 0.17 | |
F- test | 17.71 | 5.37 | 10.85 | |
df | 23 | 23 | 23 | 23 |
P- value | 0 | 0 | 0 | 0 |
The density of Anopheles species was significantly higher in the wet (April through September) than in the dry (October through March) seasons (P- value = 0.000). The mean density of Anopheles gambiae s.l. was high within the dry seasons (Table 5); however, there was no significant difference in mean density of Anopheles coustani cx. across the seasons.
Table 5
Seasonal mean density variation of Anopheles species in Wonji sugar estate, July 2018 to June 2020.
Anopheles species | Wet season | Dry season | t- test | P -value |
Mean ± SE | Mean ± SE |
Anopheles gambiae s.l. | 0.31 ± 0.01 | 0.12 ± 0.01 | 13.66 | 0.000 |
Anopheles pharoensis | 0.07 ± 0.01 | 0.05 ± 0.00 | 2.57 | 0.010 |
Anopheles coustani cx. | 0.03 ± 0.01 | 0.03 ± 0.00 | -0.45 | 0.66 |
Total | 0.36 ± 0.01 | 0.19 ± 0.01 | 11.27 | 0.000 |
The correlation analysis revealed that Anopheles species means monthly density with climate variability has strong positive correlation with monthly; mean minimum temperature and relative humidity (r = 0.24, p = 0.000&r = 0.173, p = 0.000) respectively (Fig. 3). The maximum temperature has shown significant negative correlation (r=-0.050, p = 0.029) with the density of Anopheles species. Anopheles gambiae s. l’s mean monthly density has demonstrated a strong positive correlation with mean: rainfall, minimum temperature, and relative humidity but a strong negative correlation with maximum temperature (r = 0.57, p = 0.013, r = 0.264, p = 0.000, r = 0.211, p = 0.000, and r = -0.077, p = 0.001, respectively).
The variation in mean monthly Anopheles pharoensis density has shown no correlation with: relative humidity, mean maximum and minimum temperatures (r = 0.11, p = 0.623, r = -0.039, p = 0.087, and r = -0.009, p = 0.694, respectively).
The monthly catch density of Anopheles coustani cx. has a positive correlation with mean maximum and minimum temperatures (r = 0.055 p = 0.016 & r = 0.102 p = 0.000), but a very weak correlation with average rainfall and relative humidity (r = 0.003 p = 0.909 & r = 0.016 p = 0.491). The regression analysis result justifies the minimum temperature, rainfall and relative humidity predicts the variability in mean density of Anopheles species at p-value < 0.05.