Experimental hut evaluation of bednets treated with an organophosphate (chlorpyrifos-methyl) or a pyrethroid (lambdacyhalothrin) alone and in combination against insecticide-resistant Anopheles gambiae and Culex quinquefasciatus mosquitoes.
BACKGROUND
Pyrethroid resistant mosquitoes are becoming increasingly common in parts of Africa. It is important to identify alternative insecticides which, if necessary, could be used to replace or supplement the pyrethroids for use on treated nets. Certain compounds of an earlier generation of insecticides, the organophosphates may have potential as net treatments.


METHODS
Comparative studies of chlorpyrifos-methyl (CM), an organophosphate with low mammalian toxicity, and lambdacyhalothrin (L), a pyrethroid, were conducted in experimental huts in Côte d'Ivoire, West Africa. Anopheles gambiae and Culex quinquefasciatus mosquitoes from the area are resistant to pyrethroids and organophosphates (kdr and insensitive acetylcholinesterase Ace.1R). Several treatments and application rates on intact or holed nets were evaluated, including single treatments, mixtures, and differential wall/ceiling treatments.


CONCLUSIONS
All of the treatments were effective in reducing blood feeding from sleepers under the nets and in killing both species of mosquito, despite the presence of the kdr and Ace.1R genes at high frequency. In most cases, the effects of the various treatments did not differ significantly. Five washes of the nets in soap solution did not reduce the impact of the insecticides on A. gambiae mortality, but did lead to an increase in blood feeding. The three combinations performed no differently from the single insecticide treatments, but the low dose mixture performed encouragingly well indicating that such combinations might be used for controlling insecticide resistant mosquitoes. Mortality of mosquitoes that carried both Ace.1R and Ace.1S genes did not differ significantly from mosquitoes that carried only Ace.1S genes on any of the treated nets, indicating that the Ace.1R allele does not confer effective resistance to chlorpyrifos-methyl under the realistic conditions of an experimental hut.
Asidi
Alex N
AN
London School of Hygiene & Tropical Medicine, London, WC1E 7HT, UK. Alex.asidi@lshtm.ac.uk
N'Guessan
Raphael
R
Koffi
Alphonsine A
AA
Curtis
Christopher F
CF
Hougard
Jean-Marc
JM
Chandre
Fabrice
F
Corbel
Vincent
V
Darriet
Frédéric
F
Zaim
Morteza
M
Rowland
Mark W
MW
D000110:Acetylcholinesterase / Q000235:genetics; D000818:Animals; D000852:Anopheles / Q000145:classification / Q000187:drug effects / Q000235:genetics; D001512:Bedding and Linens; D004390:Chlorpyrifos / Q000009:adverse effects / Q000031:analogs & derivatives* / Q000494:pharmacology; D003465:Culex / Q000145:classification / Q000187:drug effects / Q000235:genetics; D004338:Drug Combinations; D005260:Female; D005838:Genotype; D006801:Humans; D007303:Insect Vectors / Q000145:classification / Q000187:drug effects* / Q000235:genetics; D007305:Insecticide Resistance / Q000235:genetics; D007306:Insecticides / Q000494:pharmacology*; D008288:Malaria / Q000517:prevention & control; D009032:Mosquito Control / Q000379:methods*; D009570:Nitriles / Q000009:adverse effects / Q000494:pharmacology*; D011722:Pyrethrins / Q000009:adverse effects / Q000494:pharmacology*; D016896:Treatment Outcome
D004338:Drug Combinations; D007306:Insecticides; D009570:Nitriles; D011722:Pyrethrins; D000110:Acetylcholinesterase; D004390:Chlorpyrifos; C007031:chlorpyrifos-methyl; C037304:cyhalothrin