A total of 70 ovitraps were deployed across the 13 communes of Grand Lomé between March 2022-April 2023 (Fig. 1). The maximum number of ovitraps were set on the Bè-Est commune (n = 10), which also collected the largest number of Ae. aegypti larvae (n = 8,525) across the study period. The communes of Légbassito and Vakpossito had the lowest number of deployed traps (n = 3, each; Table 1). The collected Ae. aegypti larvae were reared in the laboratory to the adult stage. There was > 75% survivorship to the adult stage (Table 1).
Table 1
Overall incidence of Aedes aegypti larvae in Grand Lomé
Communes | Commune capitals | Traps per commune | Human Population | Ae. aegypti larvae | Incidence Ae. aegypti larvae | Adults Ae. aegypti | Incidence adults Ae. aegypti | Percentage adults |
Agoè-Nyivé 1 | Agoè-Nyivé | 4 | 317,255 | 1,788 | 5.63 | 1,578 | 4.97 | 88.26 |
Agoè-Nyivé 2 | Légbassito | 3 | 128,164 | 1,256 | 9.79 | 958 | 7.47 | 76.27 |
Agoè-Nyivé 3 | Vakpossito | 3 | 47,554 | 1,453 | 30.55 | 1,115 | 23.44 | 76.74 |
Agoè-Nyivé 4 | Togblékopé | 4 | 154,431 | 1,253 | 8.11 | 1,058 | 6.85 | 84.44 |
Agoè-Nyivé 5 | Sanguéra | 4 | 125,097 | 1,818 | 14.53 | 1,498 | 11.97 | 82.4 |
Agoè-Nyivé 6 | Adétikopé | 4 | 110,194 | 976 | 8.85 | 810 | 7.35 | 82.99 |
Golfe 1 | Bè-Est | 10 | 351,550 | 8,525 | 24.24 | 7,290 | 20.73 | 85.51 |
Golfe 2 | Bè-Centre | 6 | 136,153 | 4,824 | 35.43 | 4,053 | 29.76 | 84.02 |
Golfe 3 | Bè-Ouest | 5 | 52,769 | 6,477 | 122.74 | 5,387 | 102.08 | 83.17 |
Golfe 4 | Amoutiévé | 7 | 155,842 | 8,153 | 52.31 | 6,930 | 44.46 | 85 |
Golfe 5 | Aflao-Gakli | 7 | 169,993 | 6,354 | 37.37 | 5,310 | 31.23 | 83.57 |
Golfe 6 | Baguida | 8 | 181,561 | 6,541 | 36.02 | 5,325 | 29.32 | 81.41 |
Golfe 7 | Aflao-Sagbado | 5 | 257,813 | 3,350 | 12.99 | 2,890 | 11.20 | 86.27 |
In total, 52,768 Ae. aegypti larvae were collected in Grand Lomé across all study periods. The highest incidence of Ae. aegypti larvae was detected in Bè-Ouest commune (122.74 per 1,000 population. This was followed in overall high incidence by the communes of Amoutiévé (52.32 per 1,000 population) and Aflao-Gakli (37.38 per 1,000 population) (Table 1, Fig. 2). Agoè-Nyivé was the commune with the lowest incidence across the entire study period (Fig. 2). Traps with more than 1,000 Ae. aegypti larvae were considered high producers and were mostly concentrated in the Golfe prefecture of Grand Lomé (Fig. 2). The minimum number of larvae collected was 198 in a trapping site in the Adétikopé commune. Conversely, a total of 3,063 Ae. aegypti larvae were collected at Amoutiévé over the study period (Supplementary material).
A total of 33,127 (62.78%) of the Ae. aegypti larvae were collected in Grand Lomé during the rainy season (Table 2). The communes of Bè-Ouest, Amoutiévé, and Aflao-Gakli had the largest larval incidences during this period with 73.60, 30.08, and 23.73 per 1,000 population, respectively (Table 2, Fig. 3). Notably, these were also the same communes driving the highest incidence over the entire study period (Figs. 2 and 3). The lowest number of Ae. aegypti larvae collected in an individual trap during the rainy season was 146 at Adétikopé commune and the highest number was of 1,742 larvae in a trap from Amoutiévé commune (Supplementary material).
Table 2
Larval incidence of Aedes aegypti during the rainy season in Grand Lomé
Communes | Commune capitals | Ae. aegypti larvae | Incidence Ae. aegypti larvae | Adults Ae. aegypti | Incidence adults Ae. aegypti | Percentage adults |
Agoè-Nyivé 1 | Agoè-Nyivé | 1,190 | 3.75 | 1,040 | 3.27 | 87.39 |
Agoè-Nyivé 2 | Légbassito | 942 | 7.35 | 687 | 5.36 | 72.93 |
Agoè-Nyivé 3 | Vakpossito | 953 | 20.04 | 719 | 15.11 | 75.45 |
Agoè-Nyivé 4 | Togblékopé | 872 | 5.64 | 751 | 4.86 | 86.12 |
Agoè-Nyivé 5 | Sanguéra | 1,311 | 10.47 | 1,070 | 8.55 | 81.62 |
Agoè-Nyivé 6 | Adétikopé | 692 | 6.27 | 566 | 5.13 | 81.79 |
Golfe 1 | Bè-Est | 5,261 | 14.96 | 4,377 | 12.45 | 83.2 |
Golfe 2 | Bè-Centre | 2,883 | 21.17 | 2,284 | 16.77 | 79.22 |
Golfe 3 | Bè-Ouest | 3,884 | 73.60 | 3,066 | 58.10 | 78.94 |
Golfe 4 | Amoutiévé | 4,688 | 30.08 | 3,957 | 25.39 | 84.41 |
Golfe 5 | Aflao-Gakli | 4,034 | 23.73 | 3,260 | 19.17 | 80.81 |
Golfe 6 | Baguida | 4,121 | 22.69 | 3,352 | 18.46 | 81.34 |
Golfe 7 | Aflao-Sagbado | 2,296 | 8.90 | 1,942 | 7.53 | 84.58 |
During the dry season, a total of 19,641 (37.22%) of the Ae. aegypti larvae were collected, which was roughly half the number of larvae collected during the rainy season (Tables 3 and 2, Fig. 3). Bè-Ouest and Amoutiévé remained as the communes with the highest incidence during this period with 49.14 and 22.23 larvae per 1,000 population, respectively. The third commune with the highest incidence in this period was Bè-Centre with 14.26 larvae per 1,000 population. All incidence values were lower than those of the rainy season (Tables 2 and 3, Fig. 3). Communes including Adétikopé, Togblékopé, and Légbassito showed lower incidences overall (i.e., 2.58, 2.47, and 2.45 per 1,000 population, respectively; Table 3). The maximum number of Ae. aegypti larvae collected in an individual trap was 1,321 and the minimum was 48, which was lower than in the rainy season (Supplementary material, Fig. 3). A statistically significant difference was detected in the number of Ae. aegypti larvae collected between the rainy and dry seasons, with 1.69 times more larvae collected during the rainy season (Fig. 4, LRT = 3485.2, p < 0.001).
Table 3
Larval incidence of Aedes aegypti during the dry season in Grand Lomé
Communes | Commune capitals | Ae. aegypti larvae | Incidence Ae. aegypti larvae | Adults Ae. aegypti | Incidence adults Ae. aegypti | Percentage adults |
Agoè-Nyivé 1 | Agoè-Nyivé | 598 | 1.88 | 538 | 1.69 | 89.97 |
Agoè-Nyivé 2 | Légbassito | 314 | 2.45 | 271 | 2.11 | 86.31 |
Agoè-Nyivé 3 | Vakpossito | 500 | 10.51 | 396 | 8.32 | 79.2 |
Agoè-Nyivé 4 | Togblékopé | 381 | 2.46 | 307 | 1.98 | 80.58 |
Agoè-Nyivé 5 | Sanguéra | 507 | 4.05 | 428 | 3.42 | 84.42 |
Agoè-Nyivé 6 | Adétikopé | 284 | 2.57 | 244 | 2.21 | 85.92 |
Golfe 1 | Bè-Est | 3,264 | 9.28 | 2,913 | 8.28 | 89.25 |
Golfe 2 | Bè-Centre | 1,941 | 14.25 | 1,769 | 12.99 | 91.14 |
Golfe 3 | Bè-Ouest | 2,593 | 49.13 | 2,321 | 43.98 | 89.51 |
Golfe 4 | Amoutiévé | 3,465 | 22.23 | 2,973 | 19.07 | 85.8 |
Golfe 5 | Aflao-Gakli | 2,320 | 13.64 | 2,050 | 12.05 | 88.36 |
Golfe 6 | Baguida | 2,420 | 13.32 | 1,973 | 10.86 | 81.53 |
Golfe 7 | Aflao-Sagbado | 1,054 | 4.08 | 948 | 3.67 | 89.94 |
By categorizing the 70 ovitraps according to the number of larvae produced, 18 traps (25.71%) produced more than 1,000 larvae (considered high producers), 19 traps (27.14%) with 500-1,000 larvae (i.e., medium), and 33 traps (47.14%) with less than 500 larvae (i.e., low; Table 4). Eight land cover classes were represented by the ESA 10 m product (Table 4 and Fig. 5). The built-up category was the most common across Grand Lomé, followed by grassland and tree cover (Table 4 and Fig. 5). Visually, each buffer is composed mainly by pixels representing the built-up category and therefore suggesting a highly urban surface (Fig. 5). The Chi Square test assessing whether larval abundance categories and land cover classes were associated showed a significant relationship (X2 = 2883.5, degrees of freedom = 14, p < 0.001), thus, land cover classes can be used to differentiate Ae. Aegypti larvae abundance categories. Consistently, tree cover, shrubland, and grassland had more pixels for traps with less than 500 larvae of Ae. aegypti (i.e., low category; Table 4). Land cover classes related with presence of water (i.e., permanent water bodies and herbaceous wetland) showed a larger number of land cover pixels for traps with medium and high numbers of Ae. aegypti larvae rather than for traps with lower numbers (Table 4).
Table 4
Distribution of the number of Aedes aegypti larvae across Grand Lomé using land cover data
Land cover name | Land cover class | Total number of pixels | High larval numbers (n = 18; 25.7%) | Medium larval numbers (n = 19; 27.1%) | High + Medium numbers (n = 37; 52.9%) | Low larval numbers (n = 33; 47.1%) |
Tree cover | 10 | 2,992 | 377 | 321 | 698 | 1,596 |
Shrubland | 20 | 932 | 131 | 47 | 178 | 576 |
Grassland | 30 | 7,074 | 620 | 1,235 | 1,855 | 3,364 |
Cropland | 40 | 958 | 25 | 300 | 325 | 308 |
Built-up | 50 | 122,303 | 21,201 | 21,964 | 43,165 | 35,973 |
Bare / sparse vegetation | 60 | 656 | 142 | 71 | 213 | 230 |
Permanent water bodies | 80 | 1554 | 539 | 238 | 777 | NA |
Herbaceous wetland | 90 | 521 | 8 | 150 | 158 | 205 |
Other species of mosquito larvae were collected during this study, including 902 Anopheles spp. larvae and 1,272 Culex spp. larvae, with higher numbers found in the rainy season (Supplementary material). The significance and epidemiological consequences of these other mosquito species will be reported separately.