Insecticide Susceptibility Levels of Phlebotomus Orientalis and P. Bergeroti (Diptera: Psychodidae) From Eastern and Northern Ethiopia.
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Date
2008-07
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Addis Ababa University
Abstract
The status of insecticides resistance was investigated in wild population of P. orientalis
from Melka-Worer (Eastern Ethiopia) and Libo-Kemkem (Northern Ethiopia) and
laboratory breed P. bergeroti (F1) from collection in Melka-Worer between December
2007 and June 2008. Sand flies were exposed to six insecticides approved by WHO for
indoor residual spray (IRS) and insecticides treated nets (ITNs). Standard WHO
diagnostic bioassay kits for susceptibility studies with WHO discriminating doses of
DDT (4%), malathion (5%) and permethrin (0.75%), lambda-cyhalothrin (0.05%),
deltamethrin (0.05%), alpha-cypermethrin (0.1%) impregnated papers were used. Knock
down every 5 minute up to 20 minute and every 10 minute up to one hour and mortality
of sand flies 24 hour after one hour of exposure was recorded. In population of P.
bergeroti from Melka-Worer mortality was over 98.8% with all insecticides tested (DDT,
permethrin, deltamethrin, lambda-cyhalothrin and malathion). The lowest 50% and 95%
knock down time (KT50 and KT95) recorded were 18.2 (15.8-20.8) minutes and 31.1
(27.3-37.9) minutes respectively for DDT followed by permethrin. However,
deltamethrin revealed the weakest knock down effect with KT50 30.6 (27.6-33.9) minutes
and KT95 46.3 (41.7-53.6) minutes. Phlebotomus orientalis in Melka-Worer showed more
than 98.8% mortality to DDT, permethrin, lambda-cyhalothrin, alpha-cypermethrin, and
deltamethrin. But it showed 93.75% mortality to malathion. The lowest KT50 was found
to be 8.2 (4.1-10.7) minutes for permethrin and the lowest KT95 21.3 (19.0-27.4) minutes
for lambda-cyhalothrin. DDT showed the lowest knock down effect at both values. The
Libo-Kemkem population of P. orientalis showed over 98.8% mortality to all insecticides.
Both permethrin at KT50 and alpha-cypermethrin at KT95 showed highest knock down
effect 11.7 and 21.1 minutes, respectively. But DDT showed the lowest knock down
effect at both level. Based on WHO criteria where susceptibility is defined by mortality
rate greater than 98% 24 hour after exposure, no evidence for resistance were found. This
implies the use of these insecticides during epidemic or high prevalence of disease would
be effective to control sand flies in the study areas though the low level of resistance in P.
orientalis to malathion in Melka-Worer needs to be confirmed.
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Biology