We recently discovered infections by a microsporidium closely related to Nosema fumiferanae in field populations of the light brown apple moth, Epiphyas postvittana (Walker) (Lepidoptera: Tortricidae), in the San Francisco region of California. E. postvittana originates from Australia and was first detected in California in 2006; therefore, our aim was to identify and determine the origin of the Nosema isolate. We characterized the pathogenicity, transmission pathways, and ultrastructure of this new Nosema isolate. In addition, we sequenced fragments of commonly used genetic markers (ITS, SSU, and RPB1), and examined the phylogenetic relationships between the Nosema isolate and other microsporidian species commonly found in lepidopteran hosts. The pathogenicity of the Nosema isolate was investigated by infecting second instar larvae of E. postvittana. Larval and pupal survivorship were reduced by 7% and 13% respectively, and pupation occurred 1-2d later in infected individuals than in healthy individuals. Emerging infected females died 5d earlier than healthy females, and daily fecundity was 22% lower. Hatch rate also was 22% lower for eggs oviposited by infected females. Vertical transmission was confirmed; spores were present in 68% of egg masses and 100% of the surviving larvae from infected females. Ultrastructure images, together with sequences from selected genetic markers, confirmed the Nosema isolate to be a member of the Nosema fumiferanae species complex (Nosema fumiferanae postvittana subsp. n.). The association of this pathogen with E. postvittana contributes further to the biotic resistance that E. postvittana has experienced since its introduction to California.
Keywords: Host range; Pathogen; Phylogeny; Sublethal effects; TEM.
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