Molecular characterization of an entomopathogenic fungus: its pathogenesis in black-legged tick, Ixodes scapularis (Say) (Acari: Ixodidae)

Issue Date

4-2009

Abstract

Ticks are among the most important eight-legged pests because they carry pathogenic and symbiotic microorganisms including fungi. A fungus was isolated from a female black-legged tick, Ixodes scapularis, removed from a white-tailed deer for the identity of the fungus. The pathogenesis of the fungus in nymphs of I. scapularis was documented. The isolate (SCIs3-2) was a Beauveria species. The fungus produced smooth-walled conidia and mycelia that bore clustered flask-shaped or swollen conidiophores. The PCR amplicons of the ITS and EF1-α gene of SCIs3-2 were sequenced. The primer set ITS4 and ITS5, that targets the ITS regions of the nuclear rDNA, amplified an approximately 600 bp PCR product. Phylogenetic analyses of the ITS and EF1-α sequence revealed that isolate SCIs3-2 is Beauveria cf. bassiana, a species closely related to, but distinct from, B. bassiana sensu stricto. Conidia adhered immediately to tick cuticle and germinated 24 to 48 hours post challenge. Development of the germ tube was slow but penetration of the fungus into the hard cuticle and intersegmental membrane of legs was observed. With the formation of an appresorium, direct penetration of the germ tube was observable. There was also infection through the natural openings of the tick, i,e. pores of the spiracular plate. Growth of hyphae was directed into the cuticle and internal infection was evident 10 to 14 days post challenge. Budding blastospores and hyphae were visible in extirpated tissues. The fungus grew out of the tick's cuticle produced conidia on surface of the cadaver 20-28 days post challenge.

Source or Periodical Title

Philippine Entomologist

ISSN

0048-3753

Volume

23

Issue

1

Page

37-55

Document Type

Article

Frequency

semi-annually

Physical Description

illustrations ; tables

Language

English

En – AGROVOC descriptors

BEAUVERIA BASSIANA; IXODES SCAPPULARIS; IXODES; ACARINA; ENTOMOGENOUS FUNGI; CONIDIOPHORES; PATHOGENESIS

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