Comparison of transmission parameters between Anopheles argyritarsis and Anopheles pseudopunctipennis in two ecologically different localities of Bolivia

BACKGROUND: Anopheles (Anopheles) pseudopunctipennis is a recognized malaria vector in the slopes of the Andes of Bolivia. There, other species might be involved in malaria transmission and one candidate could be Anopheles argyritarsis. Although it is generally admitted that this species is not a malaria vector in the neotropical region, its potential role in transmission is still controversial and this situation has to be cleared, at least for Bolivia. Comparing the vectorial efficiency of An. pseudopunctipennis with that of An. argyritarsis could solve the question. METHODS: The two species were sampled throughout Bolivia to estimate their degree of co-existence in their distribution range. Vectorial efficiencies of the two species were compared in two ecologically different localities where the species were sympatric by analysing their vectorial capacities and components (i e, human biting rates, human biting index, survival, durations of the gonotrophic cycle and extrinsic cycle), and the entomological inoculation rates (EIR). Mosquitoes were sampled monthly during more than one year in the two localities. A monthly sample consisted in hourly captures in four houses (inside and outside) in each locality, during four consecutive nights. Climatic variables (temperature, humidity, potential evapo-transpiration and precipitations) were recorded to better understand variability in the entomological parameters. Relationships were analysed using multivariate methods. RESULTS: Anopheles pseudopunctipennis and An. argyritarsis are “altitude” species, sharing the same geographical distribution range in the Andes of Bolivia. No Plasmodium parasite was identified in An. argyritarsis and estimates of the vectorial capacity indicated that it is not a malaria vector in the two studied localities, unlike An. pseudopunctipennis which showed positive EIRs. This latter species, although not a very good malaria vector, exhibited better life traits values and better behavioural characteristics in favour of transmission as compared to An. argyritarsis. CONCLUSIONS: In the Andes of Bolivia, above 1000 m of altitude, An. pseudopunctipennis is likely to be the only malaria vector. There, it is present almost everywhere and priority control effort should be directed toward this species. Below 1000 m of altitude, vector incrimination should also be focused on other sympatric species (likely not An. argyritarsis) that might be locally important. From the present study, candidates would be among Anopheles rangeli, Anopheles triannulatus s.l., Anopheles trinkae, Anopheles nuneztovari s.l., Anopheles oswaldoi s.l. and Anopheles benarrochi s.l.