The digitized grid cell data was used determine abundance of rice land
Anopheles larvae in the paddy and canal habitats in each study site. The abundance of 1
st instar larvae/dip collected in Rurumi and Kangichiri study sites was 0.99 and 1.95, respectively and significantly lower than 4.81 in the Kiuria study site (F = 5.16, df 2, 751, p < 0.01). Similarly, the abundance of 2
nd instar larvae differed significantly among villages with that of 0.66 in the Rurumi study site being significantly lower than 1.09 or 2.11 in Kangichiri and Kiuria study sites, respectively (F = 3.79, df 2, 751, p < 0.05). The abundance of 3
rd and 4
th instar larvae as well as that of pupae did not differ significantly among villages (F = 1.64, 0.97 and 1.04, df 2, 75, p > 0.05). Table
1. shows the abundance of rice land
An. arabiensis larvae/20 dips collected in the paddy and canal habitats at the 3 study sites. In the Kangichiri study site, the difference in the abundance of pupae and 1
st, 2
nd and 3
rd instar larvae collected in paddy and canal habitats was not significant (p > 0.05) while that of 4
th instar larvae was significantly higher in the paddy habitats than in the canals (F = 5.19, df 1, 179, p < 0.05). In the Kiuria study site, significantly higher abundance of 3
rd instar larvae were collected in the canals (F = 4.68, df 1, 179, p < 0.05) while the other immature stages did not differ significantly between canal and paddy habitats. In the Rurumi study site, paddy habitats had significantly higher abundance of 1
st and 2
nd instar larvae compared with the canals (F = 5.60 and 3.94, df 1, 188, p < 0.05) but the other immature stages did not vary significantly between paddy and canal habitats.
Table 1
Abundance of An. arabiensis larvae in paddies and canals identified using digitized grid cell and field sampled data
Kangichiri | Paddy | 160 | 57.10 | 1.64 ± 0.38 | 1.18 ± 0.25 | 0.24 ± 0.13 | 0.00 ± 0.00 | 0.40 ± 0.13 |
| Canal | 135 | 42.90 | 2.28 ± 1.16 | 0.99 ± 0.25 | 0.17 ± 0.10 | 0.07 ± 0.03 | 0.17 ± 0.05 |
Kiuria | Paddy | 122 | 62.80 | 5.50 ± 2.00 | 1.83 ± 0.59 | 0.14 ± 0.07 | 0.37 ± 0.35 | 0.27 ± 0.11 |
| Canal | 69 | 37.20 | 3.66 ± 0.85 | 2.59 ± 0.85 | 0.40 ± 0.10 | 0.04 ± 0.03 | 0.19 ± 0.09 |
Rurumi | Paddy | 106 | 68.60 | 1.42 ± 0.34 | 1.12 ± 0.45 | 0.08 ± 0.04 | 0.05 ± 0.03 | 0.16 ± 0.11 |
| Canal | 98 | 31.40 | 0.59 ± 0.12 | 0.23 ± 0.07 | 0.11 ± 0.04 | 0.01 ± 0.01 | 0.04 ± 0.02 |
The distribution of larvae in rice fields at different stages of the rice cycle is shown in Table
2. Six stages of rice growth were identified in each of the three study sites by the digitized grid. An analysis of variance test indicated the relative abundance of immature stages of
An. arabiensis at the three study sites to be significantly higher during the post-transplanting and the tillering stages of the rice growth (P < 0.05). In the other rice stages, the immature stages of
An. arabiensis were either absent or occurring in low numbers.
Table 2
Immature stages of An. arabiensis sampled in paddies containing different stages of rice growth using digitized grid data
Kangichiri | Ploughed | 25 | 1.41 | 0.95 | 0.09 | 0.00 | 0.36 |
| Flooded | 23 | 1.67 | 1.10 | 0.30 | 0.00 | 0.36 |
| Post transplanting | 30 | 6.02 | 3.00 | 1.89 | 1.20 | 0.99 |
| Tillering | 28 | 8.00 | 6.67 | 2.00 | 3.22 | 0.67 |
| Flowering/maturation | 27 | 0.01 | 0.00 | 0.02 | 0.01 | 0.00 |
| Fallow | 27 | 1.00 | 0.67 | 0.00 | 0.00 | 0.01 |
Kiuria | Ploughed | 22 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 |
| Flooded | 23 | 1.23 | 0.65 | 0.07 | 0.01 | 0.0 |
| Post transplanting | 21 | 5.58 | 1.63 | 0.17 | 0.51 | 0.19 |
| Tillering | 22 | 8.50 | 5.25 | 0.25 | 0.25 | 1.25 |
| Flowering/maturation | 20 | 0.02 | 0.00 | 0.01 | 0.0 | 0.00 |
| Fallow | 14 | 0.03 | 0.01 | 0.0 | 0.01 | 0.00 |
Rurumi | Ploughed | 18 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 |
| Flooded | 21 | 1.56 | 1.28 | 0.09 | 0.06 | 0.19 |
| Post transplanting | 20 | 5.73 | 3.37 | 1.17 | 1.03 | 0.47 |
| Tillering | 20 | 4.91 | 4.67 | 1.19 | 1.11 | 1.00 |
| Flowering/maturation | 15 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 |
| Fallow | 12 | 1.17 | 0.00 | 0.00 | 0.00 | 0.00 |
The relative abundance of rice land
An. arabiensis larvae in vegetated and non-vegetated canal habitats identified by the digitized grid and the statistical comparisons of larval abundance between the two categories are represented in Tables
3 and
4. In the Kangichiri study site, the relative abundance of 1
st and 2
nd instar larvae was significantly higher in non-vegetated than vegetated canals while the differences in the other aquatic stages was not significant. In the Kiuria study site, the abundance of all the 4 larval instars of
An. arabiensis was significantly higher in non-vegetated canals whereas in the Rurumi study site, the same trend was observed for the 2
nd and 3
rd instar larvae.
Table 3
Average number (± SE) of An. arabiensis larvae in vegetated and non-vegetated canals using the digitized grid data
Kangichiri | Present | 1.20 ± 0.31 | 0.87 ± 0.21 | 0.00 ± 0.00 | 0.00 ± 0.00 | 0.00 ± 0.00 |
| Absent | 24.50 ± 24.50 | 3.50 ± 3.50 | 0.18 ± 0.10 | 0.07 ± 0.03 | 0.17 ± 0.05 |
Kiuria | Present | 0.00 ± 0.00 | 0.00 ± 0.00 | 0.00 ± 0.00 | 0.00 ± 0.00 | 0.00 ± 0.00 |
| Absent | 3.83 ± 088 | 2.71 ± 0.89 | 0.72 ± 0.11 | 0.5 ± 0.03 | 0.20 ± 0.09 |
Rurumi | Present | 0.4 ± 0.17 | 0.10 ± 0.10 | 0.00 ± 0.00 | 0.00 ± 0.00 | 0.00 ± 0.00 |
| Absent | 0.64 ± 0.14 | 0.27 ± 0.08 | 0.14 ± 0.05 | 0.01 ± 0.01 | 0.05 ± 0.03 |
Table 4
Statistical values comparing the differences in An. arabiensis larval densities between the vegetated and non-vegetated canals
| df | t | Sig. | df | t | Sig. | df | t | Sig. |
1st instars | 134 | 22.22 | 0.00 | 68 | 0.86 | 0.03 | 97 | 0.87 | 0.35 |
2nd instars | 134 | 4.97 | 0.03 | 68 | 0.43 | 0.04 | 97 | 3.75 | 0.05 |
3rd instars | 134 | 0.15 | 0.70 | 68 | 0.68 | 0.04 | 97 | 0.02 | 0.04 |
4th instars | 134 | 0.23 | 0.64 | 68 | 0.08 | 0.06 | 97 | 0.01 | 0.93 |
Pupae | 134 | 0.60 | 0.44 | 68 | 0.22 | 0.64 | 97 | 0.35 | 0.55 |