Experimental transmission of a microsporidian pathogen from mosquitoes to an alternate copepod host.

Abstract

Meiospores of a microsporidian parasite Amblyospora sp. (Protozoa: Microspora) from larval Aedes cantator mosquitoes were directly infectious to an alternate copepod host, Acanthocyclops vernalis (Arthropoda: Crustacea). Infections ranged from 6.7% to 60.0% in laboratory tests when meiospores and copepods were maintained together for 10-30 days in filtered water from the breeding site or in a balanced salt solution. Pathogen development takes place within host adipose tissue and is fatal to the copepod. The entire developmental sequence of this microsporidian in the copepod is unikaryotic and there is no ultrastructural evidence of a sexual cycle or a restoration of the diploid condition in the alternate host. Single uninucleated spores similar to those previously described for the genus Pyrotheca are formed. Results demonstrate that haploid meiospores of Amblyospora from mosquitoes have the function of transmitting the pathogen to another host and that members of this genus are polymorphic and have at least three distinct developmental cycles, each producing a different spore.

Review of microsporidia-mosquito relationships: from the simple to the complex

“…Studies on mosquitoes led to the discovery of dimorphism for the microsporidia and documented that a single species of microsporidia can possess two morphologically and functionally distinct spore types (Hazard and Weiser 1968). To date, the only intermediate host systems for microsporidia have been determined for species of Amblyospora (10 species) (Andreadis 1985, 1999, Sweeney et al 1985, 1990, Becnel 1992a, White et al 1994, Becnel and Andreadis 1998, Micieli et al 1998, 2000a, Para-thelohania (1 species) (Avery and Undeen 1990), Duboscqia (1 species) (Sweeney et al 1993) and Hya-linocysta (1 species) (Andreadis 2002) from mosquito hosts; all of these require an obligate copepod intermediate host to complete the life cycle. Studies on this latter group of genera have also been instrumental in understanding polymorphism in microsporidia and the role of morphologically and functionally distinctive spore types.…”

“…This represented the first clear documentation of a link between infections in adults and progeny and proved that the two morphologically distinctive spores found in larvae and adult hosts (formerly believed to belong to two genera) represented a single species. While the role of binucleate spores in transovarial transmission continued to be documented, the means by which these microsporidia were transmitted horizontally remained a mystery until the discovery that meiospores formed in larvae were infectious to a copepod intermediate host (Andreadis 1985, Sweeney et al 1985. When ingested by mosquito larvae, the spores from the copepod intermediate host initiate a sequence of development that ends with binucleate spores in the adult female mosquito.…”

Cytoplasmic male killing elements in Adalia bipunctata (Linnaeus) (Coleoptera: Coccinellidae)

“…Male killing late in the life-span, on the other hand, is interpreted not in kin selective terms, but in terms of the cytoplasmically transmitted element, at a dead-end in males, promoting the horizontal transfer of the element in the manner adopted by most pathogens: replication within the host followed by dispersal into the environment. This is known in mosquitoes, where the death of males at the fourth instar allows the release of the parasite into the environment (Andreadis, 1985). The timing of male death is held to reflect the optimal proliferation time of the parasite within the organism .…”

Evolutionary strategies and adaptations for survival between mosquito-parasitic microsporidia and their intermediate copepod hosts: a comparative examination of Amblyospora connecticus and Hyalinocysta chapmani (Microsporidia: Amblyosporidae)

“…Amblyospora connecticus has a complex life cycle that includes host sex-dependent polymorphic development, the production of three morphologically and functionally distinct spore types, maternal-mediated vertical (transovarial) transmission, and horizontal transmission via obligatory development in an intermediate copepod host (Andreadis 1983(Andreadis , 1985a(Andreadis , 1988a(Andreadis , b, 1990. The life cycle is illustrated in Fig.…”