Nosema portugal, N. SP., isolated from gypsy moths (Lymantria dispar L.) collected in portugal

A microsporidium Nosema portugal n. sp. was isolated from gypsy moths, Lymantria dispar L, collected near Lisbon, Portugal, in 1985. The life cycle includes two sequential developmental cycles, a primary and a secondary cycle. The primary cycle occurs in midgut epithelial cells, where primary spores are produced within 48 h. The primary spores immediately extrude their polar filaments, presumably to infect other cells. In the target tissues (salivary glands and fat body) the secondary development cycle is followed by the formation of environmental spores. Primary spores were also sometimes present in target tissues. Fresh unfixed and unstained primary spores have a large posterior vacuole and measured 4.8 x 2.7 &mgr;m. Ultrastructurally, they have 5-8 polar filament coils, a large posterior vacuole, abundant endoplasmic reticulum, and were binucleate. Mature unfixed and unstained environmental spores were highly refractive and the posterior vacuole and nuclei could not be seen through the spore coat. Fresh environmental spores measured 4.5 x 1.9 &mgr;m. Ultrastructurally, environmental spores were binucleate, with a typical polaroplast, 10-11 isofilar polar filament coils, and a series of 4-6 thin polar filament-like tubules situated at the posterior end of the row of typical polar filament coils. The ssu rRNA sequences strongly suggest that this species is more closely related to the Vairimorpha subgroup within the Nosema/Vairimorpha clade than to the Nosema subgroup. Copyright 1999 Academic Press.

Timing of an early sporulation sequence of microsporidia in the genus vairimorpha (Microsporidia: burenellidae)

An early sporulation event in the host midgut tissues has been reported for several species of microsporidia infecting Diptera, Hymenoptera, and Lepidoptera. The role of these primary spores, formed between 35 and 96 h postinfection per os, has been suggested to be the cell to cell spread of infection within the host, but the sequence of events during the early sporulation stages has been reported for only a few species of microsporidia. We investigated these early life cycle events for two species of microsporidia, Vairimorpha necatrix and Vairimorpha sp. from Lymantria dispar, tested in the laboratory hosts Spodoptera exigua and L. dispar, respectively. We injected hemolymph drawn from orally infected host larvae into uninfected larvae at time periods from 2 to 96 h postinfection to determine the timing of infection of the hemolymph and target tissues. Our studies demonstrated that, for both Vairimorpha species, the early sporulation in the midgut tissues is a discrete first stage of infection. Invasion of the hemolymph and infection of the target tissues follows maturation of "primary spores" in the midgut and coincides with the germination of these spores beginning approximately 30 h postinfection for hosts held at a constant 24 degreesC. The developmental stages of the microsporidia observed in the target tissues at specific time periods postinfection corresponded to the stages observed in the hemocytes, suggesting that sporoplasms from the germinating primary spores are directly injected into the target tissues and the hemolymph. Copyright 1998 Academic Press.

Sugar Acquisition during the Development of Microsporidian (Microspora: Nosematidae) Spores

Helicoverpa zea larvae were infected with Vairimorpha necatrix. The fat body was triturated and sporulation stages were fractionated according to buoyant density by Ludox density gradient centrifugation. Spores and sporulation stages formed two minor bands with buoyant densities of 1.072 and 1.121 g/ml, and two major bands with buoyant densities of 1.150 and 1.198 g/ml. The higher bands of less dense sporoblastic stages first appeared 96 hr following infection and the band containing the heaviest (1.198 g/ml) and most refringent mature spores appeared last, ca. 24 hr after the appearance of the other bands. Although the bands remained in the same relative positions regardless of the time after inoculation, the percentage of spores in Band 4 increased with time. The concentration of sugar in the spores from the 1.198-g/ml band was more than four times the concentration found in spores in the 1.150-g/ml band and accounted for more than 60% of the increase in spore weight between the two density classes. Similar tests with Nosema algerae yielded similar results, with sugars accounting for 88% of the increased spore weight. Sugar acquisition appears to occur during the attainment of the final spore density and perhaps signals spore maturation.

Host Specificity of Microsporidia (Protista: Microspora) from European Populations of Lymantria dispar (Lepidoptera: Lymantriidae) to Indigenous North American Lepidoptera

Results of traditional laboratory bioassays may not accurately represent ecological (field) host specificity of entomopathogens but, if carefully interpreted, may be used to predict the ecological host specificity of pathogens being considered for release as classical biological control agents. We conducted laboratory studies designed to evaluate the physiological host specificity of microsporidia, which are common protozoan pathogens of insects. In these studies, 49 nontarget lepidopteran species indigenous to North America were fed five biotypes of microsporidia that occur in European populations of Lymantria dispar but are not found in North American populations of L. dispar. These microsporidia, Microsporidium sp. from Portugal, Microsporidium sp. from Romania, Microsporidium sp. from Slovakia, Nosema lymantriae, and Endoreticulatus sp. from Portugal, are candidates for release as classical biological control agents into L. dispar populations in the United States. The microsporidia produced a variety of responses in the nontarget hosts and, based on these responses, the nontarget hosts were placed in the following categories: (1) no infection (refractory), (2) atypical infections, and (3) heavy infections. Endoreticulatus sp. produced patent, host-like infections in nearly two-thirds of the nontarget hosts to which it was fed. Such generalist species should not be recommended for release. Infections comparable to those produced in L. dispar were produced in 2% of the nontarget hosts fed Microsporidium sp. from Portugal, 19% of nontarget hosts fed Microsporidium sp. from Romania, 13% fed spores of Microsporidium sp. from Slovakia, and 11% of nontarget species fed N. lymantriae. The remaining nontarget species developed infections that, despite production of mature spores, were not typical of infection in L. dispar. We believe it is very unlikely that these atypical infections would be horizontally transmitted within nontarget insect populations in the United States.