Determination of efficacy of the four formulations in simulated
ponds
The trial was carried out in a screen house (7 x 3.5 x 2 m)
built on a pesticide free area at the ICIPE ground. The walls of the
screen house were made of netting material from the ground up to
1 m high and the roof was covered with a polyethene sheet (λmax =
205 nm). A total of 36 circular pools were dug in the ground of the
screen house to fit large cylindrical plastic dishes of 50 cm
diameter and 20 cm height. The dishes were filled with 3 litres of
spring water collected from Githurai River, Nairobi. The inside of
the dishes was smeared with a thin layer of mud from the floor of
the screen house to mimic the environment of natural aquatic
mosquito ponds. Early third instar An. gambiae s.s. Giles mosquito
larvae (100 in number) were introduced into each of the artificial
habitats and left for one hour to allow them to get acclimatized
before introducing test samples. Based on the preliminary
laboratory evaluation of these formulations, three concentrations
of methanolic extracts (50, 100 and 200 μg/ml) and powders of
plant materials (750, 1500 and 3000 mg) were selected to be
investigated at semi-field level. The ponds were covered with
modified ‘Saliternick’ mosquito cages (50 x 50 x 50 cm) which
were made from iron rods and covered with a net to prevent the
escape of emerging adults. Larval and pupal densities and
emergence of the adults was monitored after every 24 h. Standard
dipping technique with an enamel bowl (400 ml) was used to
sample larvae and pupae. This technique involves immersing a
mosquito dipper (enamel bowl, with a long handle) in ponds at an
angle of 45o (WHO, 2005).