Email updates

Keep up to date with the latest news and content from BMC Infectious Diseases and BioMed Central.

Open Access Research article

Increase in susceptibility to insecticides with aging of wild Anopheles gambiae mosquitoes from Côte d’Ivoire

Mouhamadou S Chouaibou1*, Joseph Chabi2, Georgina V Bingham3, Tessa B Knox4, Louis N’Dri2, Nestor B Kesse1, Bassirou Bonfoh1 and Helen V Pates Jamet3

Author Affiliations

1 Centre Suisse de Recherche Scientifique en Cote d’Ivoire (CSRS), Abidjan, 01BP1303, Côte d’Ivoire

2 Vestergaard Frandsen, 13 Aborlebu Crescent North Labone, P. O. Box KA 30201, KIA, Accra, Ghana

3 Vestergaard Frandsen, Chemin de Messidor 5-7, Lausanne, CH - 1006, Switzerland

4 Vestergaard Frandsen, Waiyaki Way, ABC Place, PO Box 66889–00800, Nairobi, Kenya

For all author emails, please log on.

BMC Infectious Diseases 2012, 12:214  doi:10.1186/1471-2334-12-214

Published: 13 September 2012

Abstract

Background

Appropriate monitoring of vector insecticide susceptibility is required to provide the rationale for optimal insecticide selection in vector control programs.

Methods

In order to assess the influence of mosquito age on susceptibility to various insecticides, field-collected larvae of An. gambiae s.l. from Tiassalé were reared to adults. Females aged 1, 2, 3, 5 and 10 days were exposed to 5 insecticides (deltamethrin, permethrin, DDT, malathion and propoxur) using WHO susceptibility test kits. Outcome measures included the LT50 (exposure time required to achieve 50% knockdown), the RR (resistance ratio, i.e. a calculation of how much more resistant the wild population is compared with a standard susceptible strain) and the mortality rate following 1 hour exposure, for each insecticide and each mosquito age group.

Results

There was a positive correlation between the rate of knockdown and mortality for all the age groups and for all insecticides tested. For deltamethrin, the RR50 was highest for 2 day old and lowest for 10 day old individuals. Overall, mortality was lowest for 2 and 3 day old individuals and significantly higher for 10 day old individuals (P < 0.05). With permethrin, the RR50 was highest for 1 to 3 day old individuals and lowest for 10 day old individuals and mortality was lowest for 1 to 3 day old individuals, intermediate for 5 day old and highest for 10 day old individuals. DDT did not display any knockdown effect and mortality was low for all mosquito age groups (<7%). With malathion, the RR50 was low (1.54 - 2.77) and mortality was high (>93%) for all age groups. With propoxur, no knockdown effect was observed for 1, 2 and 3 day old individuals and a very low level of mortality was observed (< 4%), which was significantly higher for 5 and 10 day old individuals (30%, P < 0.01).

Conclusion

Results indicate that for An. gambiae s.l. adults derived from wild-collected larvae, there was an influence of age on insecticide susceptibility status, with younger individuals (1 to 3 days old) more resistant than older mosquitoes. This indicates that the use of 1 – 2 day old mosquitoes in susceptibility assays as recommended by the WHO should facilitate detection of resistance at the stage where the highest rate of the resistance phenotype is present.

Keywords:
Anopheles gambiae age; Insecticide resistance; Vector control