Abstract:
One way of evaluating insecticide formulations against malaria vector is to undertake insecticide
decay rate study for insecticide deposits on different Wall Surfaces using WHO cone assay. To
assess the decay rate of an insecticide deposits against adult female Anopheles mosquitoes, cone
bioassay test was conducted at different time intervals after the application of each candidate
insecticide on different wall surfaces. Therefore, the residual life of three candidate pyrethroid
insecticide formulations (deltamethrine 25%WG, lambdacyhalothrin 10%WP and
lambdacyhalothrin 10%CS) was evaluated on three different wall surfaces under field conditions
at two selected sites in Jimma zone. Deltamethrine 25%WG, lambdacyhalothrin 10%WP and
lambdacyhalothrin 10%CS were sprayed at the rate of 0.02-0.025, 0.02- 0.03 and 0.02- 0.025 gm
a.i /m2, respectively on different wall surfaces (painted, plastered and non plastered) of
randomly selected houses. Mean knockdown and mortality rates of An. gambiae s.l. exposed to
different wall surfaces sprayed with the different candidate insecticide formulations were
determined from April to August 2014. During the assay, WHO cones were fixed at three pointes
(0.5m, 1.0m & 1.5m) to the sprayed and control wall surfaces. The results of the study showed
that at week one, the highest mortality rates of mosquitoes exposed to painted surface sprayed
with labdacyaholtherin 10% WP and deltametherin 25% WG were 89.3% and 88%, respectively
while the lowest mortality rates of mosquitoes exposed to non-plastered and plastered surfaces
sprayed with labdacyaholtherin 10% CS were 72% and 68.6%, respectively. The mean mortality
rates of mosquitoes exposed to painted wall surfaces sprayed with the three insecticide
formulations was 48%. There was significant difference in mean knockdown and mortality rates
of populations An. gambiae s.l. between time of test and insecticide formulations (p < 0.05.).
Moreover, there was significant difference in mean knockdown rates of An. gambiae s.l. among
wall surface types. There was no significant difference in mean mortality rates of An. gambiae
s.l. among the three different wall surfaces (P > 0.05). In conclusion, populations of An.
gambiae s.l. showed resistance against the three candidate insecticide formulations.
