Host specificity of microsporidia pathogenic to forest Lepidoptera

The host specificity of microsporidian pathogens of Lepidoptera was studied in Bulgaria where native populations of Lymantria dispar and their endemic microsporidia occur. L. dispar and sympatric lepidopteran larvae were coll ected from four sites in central and western Bulgaria. Three species of mic rosporidia, Vairimorpha sp., Nosema sp,, and Endoreticulatus sp, are known to be endemic in three L. dispar populations, with one species in each popu lation. No microsporidia were found in a fourth L. dispar population. In ad dition to the L. dispar microsporidia, 11 isolates of microsporidia were re covered from the 1494 individual lepidopteran hosts collected in these site s. When fed to L. dispar, 3 isolates produced infections that were atypical of infections in the natural hosts; one additional isolate produced an aty pical infection in Spodoptera exigua. A Nosema sp. isolated from a noctuid host produced heavy infections in L. dispar larvae, Sequencing revealed tha t the noctuid microsporidium and the closely related Vairimorpha sp, and No sema sp, microsporidia from L. dispar are distinctly different isolates. Th ese investigations strengthen previous laboratory predictions of narrow hos t ranges for the Nosema and Vairimorpha microsporidia recovered from L. dis par in Europe. In addition, the Endoreticulatus sp., which was predicted fr om laboratory studies to be a generalist, was not found in Lepidoptera spec ies sympatric with L. dispar. The results from our study indicate that labo ratory testing may considerably underestimate the host specificity of many terrestrial microsporidia, Nevertheless, infectivity to nontarget hosts in the laboratory may set the stage for understanding the evolution of closely related microsporidia found in different host species. (C) 2000 Academic P ress.