Identification of two species within the Anopheles minimus complex in northern Vietnam and their behavioural divergences

Abstract

Elucidating the complex taxonomic status of the major malaria vector taxa and characterising the individual species within each complex is important for understanding the complexity of the vector system in the south-east Asian region and will allow to estimate the impact of vector control measures. This applies to countries such as Laos, Cambodia and Vietnam that spend about 60% of their malaria control budget on implementing vector control activities. We used isozyme electrophoresis to clarify the Anopheles minimus s.l. species composition in northern Vietnam and identify behavioural divergences of individual species. Using different collection methods, adult mosquitoes were caught at monthly intervals from June to November 1995 in four villages. An. minimus s.l. could be distinguished from closely related species, An. aconitus and An. jeyporiensis, at the Octanol dehydrogenase (Odh) enzyme locus. Significant positive Fis values gave clear evidence of nonrandom mating within the An. minimus s.l. population. The highest heterozygote deficiency was observed at locus Odh, which was diagnostic for 2 sympatric An. minimus species in Vietnam similar to the An. minimus A and C species known from Thailand. We found no evidence for restricted gene flow between monthly samples, villages, or collection methods in either of the two An. minimus species. They occurred in sympatry, but in different proportions depending on the collection site, and had dissimilar resting and biting behaviours. Thus a vector control strategy will have a nonuniform effect on the various components of this diverse vector system.

Population genetic structure of the malaria vector Anopheles minimus A in Vietnam

“…minimus A is more anthropophilic and endophilic than An. minimus C (Van Bortel et al, 1999). Neither species showed genetic differentiation between populations 50 km apart, and no genetic differences between samples collected by different collection methods (Van Bortel et al, 1999).…”

“…minimus complex were identified using Octanol dehydrogenase (Odh) allozyme profiles (Van Bortel et al, 1999). When Odh could not be scored, identification was done by the polymerase-chain reaction restriction fragment length polymorphism (PCR-RFLP) assay developed by Van Bortel et al (2000).…”

“…Idh-2 was, however, not used for the analysis of population structure since it was not consistently scored in Tinh Quang. Sample preparation and electrophoresis were performed as described in Smits et al (1996) and Van Bortel et al (1999).…”

“…minimus C (Van Bortel et al, 1999). Neither species showed genetic differentiation between populations 50 km apart, and no genetic differences between samples collected by different collection methods (Van Bortel et al, 1999). In Thailand, Sharpe et al (2000) found more mitochondrial DNA (mtDNA) variation within populations than between populations originating from different provinces and concluded that neither An.…”

“…An. minimus C is found in northern Vietnam, a few localities in Thailand and in southern China (Green et al, 1990;Van Bortel et al, 1999;Sharpe et al, 2000;Chen et al, 2002). An.…”