The development of GFP-expressing Metarhizium anisopliae (Hypocreales:Clavicipitaceae) on susceptible and resistant ticks (Acari: Ixodidae)

Abstract: The fungus Metarhizium anisopliae (Hypocreales: Clavicipitaceae) is an efficientbiological control agent of various arthropods, actively penetrating host cuticles via penetrationpegs, colonizing the host body, and causing host death. Laboratory assays against various hosts(ticks and insect) have revealed that while some hosts are highly susceptible to fungus, otherhosts are resistant to its infection. Results of previous studies of the factors involved in hostsusceptibility have suggested that cuticular compounds from susceptible and resistant hosts maydifferentially influence fungus development. This work describes the microscopic developmentof a GFP-expressing M. anisopliae strain on susceptible tick (Acari: Ixodidae), Rhipicephalusannulatus, and the resistant tick, Hyalomma excavatum. Conidia were observed germinating onall hosts examined. However, the fungus was observed penetrating the cuticles of the susceptiblehosts only and never into the resistant hosts. Moreover, growth of germinating conidia and thehyphae that developed from them was inhibited on resistant hosts and died within a few days.Analyzing these observations provides new information on the specificity and importance of eachevent of the host-pathogen interaction for a successful mycosis.