Abstract
Artificial infection of mosquitoes with the endosymbiont bacteria Wolbachia can interfere with malaria parasite development. Therefore, the release of Wolbachia-infected mosquitoes has been proposed as a malaria control strategy. However, Wolbachia effects on vector competence are only partly understood, as indicated by inconsistent effects on malaria infection reported under laboratory conditions. Studies of naturally-occurring Wolbachia infections in wild vector populations could be useful to identify the ecological and evolutionary conditions under which these endosymbionts can block malaria transmission. Here we demonstrate the occurrence of natural Wolbachia infections in three species of black fly (genus Simulium), which is a main vector of the avian malaria parasite Leucocytozoon. Prevalence of Leucocytozoon was high (25%), but the nature and magnitude of its association with Wolbachia differed between black fly species. Wolbachia infection was positively associated with avian malaria infection in S. cryophilum, negatively associated in S. aureum, and unrelated in S. vernum. These differences suggest that Wolbachia interacts with the parasite in a vector host species-specific manner. This provides a useful model system for further study of how Wolbachia influences vector competence. Such knowledge, including the possibility of undesirable positive association, is required to guide endosymbiont based control methods.
Highlights
Wolbachia is the most common intracellular bacterium in insects and other invertebrates, infecting an estimated 40% of insect species[1]
Three species dominated the black fly community at Scottish forest sites from May to October 2015 (Table 1): Simulium aureum, S. vernum and S. cryophilum, with 4 additional species making up the remainder (Table 1)
Our analysis of black fly populations reveals for the first time the presence of seasonally stable Wolbachia and avian malaria infection in 3 Simulium species
Summary
Wolbachia is the most common intracellular bacterium in insects and other invertebrates, infecting an estimated 40% of insect species[1]. As creating stable lines of Wolbachia in Anopheles is very challenging, other studies have investigated the effect of Wolbachia on malaria parasites by directly infecting adult Anopheles mosquitoes with the endosymbiont; this process differs from stable transinfections as it does not result in the transmission of Wolbachia to the progeny. Two studies investigated the role of natural Wolbachia infection by curing endosymbiont infections in Aedes and Culex species with antibiotics and observing changes in susceptibility to avian malaria parasites. In both cases (Ae. fluviatilis and Cx. pipiens), antibiotic treatment led to a reduced susceptibility to avian malaria parasites (P. gallinaceum and P. relictum, respectively)[25,26]. The specificities of these tripartite host–parasite and endosymbiont associations in natural systems are poorly understood
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