An Ultrastructural Study of Vairimorpha necatrix (Microspora, Microsporida) with Particular Reference to Episporontal Inclusions During Octosporogony

Abstract

ABSTRACT. The life cycle of Vairimorpha necatrix was studied by electron microscopy. Disporous development has two distinct stages: 1) diplokaryotic meronts which are actively mitotic, and 2) diplokaryotic sporonts which are distinguished by reduced ribosome density and a thickened plasmalemma. After final division of the sporont, sporoblasts form spores which are ovocylindrical and measure 4.4 ± 0.08 × 2.3 ± 0.05 μm (mean ± SE). Octosporous development results in eight haploid spores being formed in a sporophorous vesicle. The uninucleate octospores were smaller than the binucleate dispores and the exospore was thicker but less crenulate in outline. Early in octosporogony, tubules are produced from the sporont plasmalemma and electron‐dense material accumulates in the episporontal space. The latter may be amorphous, vesiculated, or vacuolated in appearance and in later stages may take a stacked, lamellar form. At sporoblast formation, exospore material coats the plasmalemma and attached tubules; all inclusions in the episporontal space gradually disappear as spores are formed. These secretory products may have application to taxonomic distinction at the species level.

A new isolate of the microsporidium Vairimorpha necatrix (Microsporidia, Burenellidae) recorded in the azores

“…Ultrastructural observations were consistent with descriptions of V. necatrix developing in Helicoverpa (Heliothis) zea (Boddie) (Moore and Brooks, 1992;Mitchell and Cali, 1993). Mature diplokariotic spores had a long narrow morphology (Fig.…”

Vairimorpha disparis n. comb. (Microsporidia: Burenellidae): A Redescription and Taxonomic Revision of Thelohania disparis Timofejeva 1956, a Microsporidian Parasite of the Gypsy Moth Lymantria dispar (L.) (Lepidoptera: Lymantriidae)

“…The type species of the genus, V. necatrix (Kramer 1965), although of low host specificity, is clearly a different species. The number of polar filament coils is different for spores produced in the S2ss and S2oct cycles, and secretory products in the episporontal space are lamellar rather than web‐like (Moore and Brooks 1992). Differences are also found among other lepidopteran Vairimorpha species (Table 3).…”

A new microsporidian species, Vairimorpha ocinarae n. sp., isolated from Ocinara lida Moore (Lepidoptera: Bombycidae) in Taiwan

“…15), but they did not develop into an amorphous mass or meshwork like that observed in V. necatrix (Moore and Brooks, 1992;Mitchell and Cali, 1993), V. disparis (Vavra et al, 2006), and V. heterosporum (Moore and Brooks, 1994). Moore and Brooks (1994) proposed that episporontal inclusions may be used as taxonomic features among species.…”

“…Typically, the fat body is the primary target tissue for lepidopteran Vairimorpha species, and cells are often hypertrophic and filled with both diplokaryotic spores and octospores (Canning et al, 1999;Darwish et al, 1989;Mitchell and Cali, 1993;Moore and Brooks, 1992;Moore and Brooks, 1994), unlike the fat body atrophy observed in V. ocinarae infections.…”