Staggered larval time-to-hatch and insecticide resistance in the major malaria vector Anopheles gambiae S form

• Published in: Malaria journal 2010-12, Vol.9 (1), p.360-360, Article 360
• Main Authors: Kaiser, Maria L, Koekemoer, Lizette L, Coetzee, Maureen, Hunt, Richard H, Brooke, Basil D
• Format: Article
• Language: English
• Subjects: Animals; Anopheles; Anopheles - drug effects; Anopheles - growth & development; Anopheles gambiae; Aquatic insects; Aquatic organisms; Bio-assays; Bioassays; Breeding; Colonies; Colonies & territories; Congo; Crosses, Genetic; Detoxification; Disease Vectors; Drug therapy; Eggs; Experiments; Female; Females; Genetic aspects; Genetic crosses; Ghana; Hatching; Health aspects; Heredity; Human diseases; Insecticide Resistance; Insecticides; Insecticides - pharmacology; Laboratories; Larva - drug effects; Larva - growth & development; Larvae; Malaria; Mosquitoes; Mutation; Offspring; Pesticide resistance; Phenotypes; Phenotypic variations; Pleiotropy; Progeny; Resistance mechanisms; S form; Vector-borne diseases
• ISSN: 1475-2875; 1475-2875
• DOI: 10.1186/1475-2875-9-360

Anopheles gambiae is a major vector of malaria in the West African region. Resistance to multiple insecticides has been recorded in An. gambiae S form in the Ahafo region of Ghana. A laboratory population (GAH) established using wild material from this locality has enabled a mechanistic characterization of each resistance phenotype as well as an analysis of another adaptive characteristic - staggered larval time-to-hatch. Individual egg batches obtained from wild caught females collected from Ghana and the Republic of the Congo were monitored for staggered larval time-to-hatch. In addition, early and late larval time-to-hatch sub-colonies were selected from GAH. These selected sub-colonies were cross-mated and their hybrid progeny were subsequently intercrossed and back-crossed to the parental strains. The insecticide susceptibilities of the GAH base colony and the time-to-hatch selected sub-colonies were quantified for four insecticide classes using insecticide bioassays. Resistance phenotypes were mechanistically characterized using insecticide-synergist bioassays and diagnostic molecular assays for known reduced target-site sensitivity mutations. Anopheles gambiae GAH showed varying levels of resistance to all insecticide classes. Metabolic detoxification and reduced target-site sensitivity mechanisms were implicated. Most wild-caught families showed staggered larval time-to-hatch. However, some families were either exclusively early hatching or late hatching. Most GAH larvae hatched early but many egg batches contained a proportion of late hatching larvae. Crosses between the time-to-hatch selected sub-colonies yielded ambiguous results that did not fit any hypothetical models based on single-locus Mendelian inheritance. There was significant variation in the expression of insecticide resistance between the time-to-hatch phenotypes. An adaptive response to the presence of multiple insecticide classes necessarily involves the development of multiple resistance mechanisms whose effectiveness may be enhanced by intra-population variation in the expression of resistance phenotypes. The variation in the expression of insecticide resistance in association with selection for larval time-to-hatch may induce this kind of enhanced adaptive plasticity as a consequence of pleiotropy, whereby mosquitoes are able to complete their aquatic life stages in a variable breeding environment using staggered larval time-to-hatch, giving rise to an adult population with enha