Figure 1.
Ahero Irrigation scheme, sampling points for area sampler and emergence trap.
Layout of rice paddies (1 acre each) in the Ahero Irrigation scheme (total area 2,168 acres) and location of the scheme in Kenya. The Ahero Irrigation Research Station (AIRS) is located within the scheme. The river Nyando is the water source for the scheme. a: Sketch of the entire scheme (courtesy of AIRS) and b: Schematic diagram showing the nine sampling points for the area sampler in a rice paddy, the emergence trap and the positions to which the emergence trap was moved.
Figure 2.
Timeline for rice growth, maintenance and application of Aquatain.
The dashed horizontal line indicates the water level that was maintained during various stages of rice crop and drainage 10–14 days before harvest. The diagram also shows when a herbicide, nitrogenous fertiliser, and an insecticide were applied to the rice paddies. Broken arrows represent the two applications of Aquatain.
Figure 3.
Emergence trap, field bioassay and evaporation measurement.
a. Floating emergence trap. Arrow indicates the sleeve used to aspirate the adult mosquitoes and non-target organisms. b. Bucket used for the field bioassay on Aquatain efficacy. Arrow indicates the 25 cm2 holes at the bottom. c. Tubs with 15 rice plants, planted in a 20 cm soil layer. A 4 cm water layer was added to these tubs to measure evaporation.
Figure 4.
Air temperature and rainfall during the study period.
Daily air temperature (minimum and maximum, °C) and rainfall (mm) measured during the study period (courtesy of AIRS).
Figure 5.
Average number (±S.E.) of early (L1–2) and late (L3–4) anopheline and culicine larvae per sampling site.
Average (± SE; n = 6) of early stage (L1–2) and late stage (L3–4) anopheline and culicine larvae per sampling point. The broken arrow indicates the first Aquatain application (1 ml/m2). The solid arrow represents the second Aquatain application (2 ml/m2). The square brackets on the top represent the overall comparison of the control and treated paddies before application (pre-application, 5/4–3/5) and after first (11/5–21/5) and second application (28/5–7/6). n.s., non-significant; *, p<0.05; **, p<0.01; ***, p<0.001 (Generalized estimating equations). Similar small case letters on every bar represent no significant difference (t-test, p<0.05) in the control and treatment paddies on that sampling date.
Table 1.
Average number (S.E.) of larvae, pupae and adults collected before and after Aquatain applications.
Figure 6.
Average number of anopheline and culicine adults in the emergence trap.
Average number (± SE; n = 6) of anopheline and culicine adults collected in the emergence trap per day in the control and treatment paddies before application (pre-application) and after first and second application. n.s., non-significant; *, p<0.05; ***, p<0.001 (Generalized estimating equations).
Figure 7.
Water level and volume as a measure of water loss due to evaporation.
a: The water level (cm) in the control and treated tubs (with rice plants and soil) on each sampling date. Arrows represent Aquatain application (1 ml/m2). b: The volume of water lost (Liters) from the control and treatment tubs in the assays (without rice plants and soil).
Table 2.
Average number ± S.E. (total number) of non-target organisms collected with the area sampler or emergence traps.
Table 3.
Average (S.D.) Plant height, plant density, number of tillers and crop yield in the control and treatment paddies.