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Vairimorpha imperfecta n.sp., a microsporidian exhibiting an abortive octosporous sporogony in Plutella xylostella L. (Lepidoptera: Yponomeutidae)

Published online by Cambridge University Press:  01 September 1999

E. U. CANNING ,
A. CURRY ,
S. CHENEY ,
N. J. LAFRANCHI-TRISTEM  and
M. A. HAQUE
E. U. CANNING
Affiliation:
Department of Biology, Imperial College of Science, Technology and Medicine, London SW7 2AZ
A. CURRY
Affiliation:
Public Health Laboratory, Withington Hospital, Manchester M20 2LR
S. CHENEY
Affiliation:
Department of Biology, Imperial College of Science, Technology and Medicine, London SW7 2AZ
N. J. LAFRANCHI-TRISTEM
Affiliation:
Department of Biology, Imperial College of Science, Technology and Medicine, London SW7 2AZ
M. A. HAQUE
Affiliation:
Present address: Department of Entomology, Bangladesh Agricultural University, Mymensingh 2202, Bangladesh.
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Abstract

The microsporidian genus Nosema is characterized by development in direct control with host cell cytoplasm, diplokaryotic nuclei throughout development and disporous sporogony. The genus Vairimorpha exhibits the same features plus an octoporous sporogony producing uninucleate spores in a sporophorous vesicle. A microsporidium from diamondback moth, Plutella xylostella, falls between Nosema and Vairimorpha in that it initiates but fails to complete the octosporous sequence in this host. The name Vairimorpha imperfecta n.sp. is proposed. Merogony is mainly by formation of buds from multinucleate meronts, the buds remaining attached in chains. Diplokaryotic spores measure 4·3×2·0 μm (fresh) and have 15·5 coils of the polar tube in 1 rank. The octosporous sporogony is aborted owing to irregular formation of nuclear spindles, incomplete cytoplasmic fission and bizarre deposition of electron-dense episporontal secretions. Phylogenetic analyses of the sequences of the small subunit rRNA genes of V. imperfecta and of several Nosema and Vairimorpha spp. place V. imperfecta in a clade with Nosema spp. from Lepidoptera rather than in the clade containing the more typical species of Vairimorpha. It is suggested that the ancestors of the Vairimorpha/Nosema complex of species exhibited both disporous and octosporous sporogonies, as does the type species of Vairimorpha, Vairimorpha necatrix. It would follow that true Nosema spp. have lost the ability to express an octosporous sequence and that V. imperfecta is in the process of losing it. It is proposed that the genera Nosema and Vairimorpha be placed in the same family Nosematidae Labbé 1899, rather than in separate families and orders as at present.

Keywords

Vairimorpha imperfecta n.sp.Plutella xylostellaultrastructurerDNA sequencegenetic analysis
Type
Research Article
Information
Parasitology , Volume 119 , Issue 3 , September 1999 , pp. 273 - 286
Copyright
1999 Cambridge University Press

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