Submitted to: Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/18/2012
Publication Date: 5/15/2012
Citation: Ment, D., Churchill, A.C., Gindin, G., Belausov, E., Glazer, I., Rehner, S.A., Rot, A., Donzelli, B.G., Samish, M. 2012. Resistant ticks inhibit Metarhizium infection prior to hemocoel invasion by reducing fungal viability on the cuticle surface. Environmental Microbiology. 14(6):1570-1583. Interpretive Summary: Ticks and tick-transmitted diseases are major problems in cattle production. Although some fungi are known to be capable of controlling ticks, determining which fungi are the most effective requires knowledge of the way that fungi invade the ticks. In this research tick-killing fungi were marked with a fluorescent substance so that researchers could observe the processes involved in invading and destroying the ticks. The fluorescent substance revealed that certain fungus isolates could penetrate the hard outside surface of the tick and then kill it. Thus, the use of the fluorescent substance provides a significant new method for determining the efficacy of fungi in controlling ticks. This research will be used by scientists who are working to control cattle ticks without the use of harmful chemicals.
Technical Abstract: We studied disease progression of, and host responses to, four species in the M. anisopliae complex expressing green fluorescent protein (GFP). We compared development and determined their relative levels of virulence against two susceptible arthropods, the cattle tick Rhipicephalus annulatus and the lepidopteran Galleria mellonella, and two resistant ticks, Hyalomma excavatum and R. sanguineus. M. brunneum Ma7 caused the greatest mortality of R. annulatus, M. robertsii ARSEF 2575 and M. pingshaense PPRC51 exhibited intermediate levels of virulence, and M. majus PPRC27 caused low mortality of cattle ticks. Conidia of all four species germinated on all hosts examined, but on resistant hosts, sustained hyphal growth was inhibited and GFP emission steadily and significantly decreased over time, suggesting a loss of fungal viability. Cuticle penetration was observed only for the three most virulent species infecting susceptible hosts. Cuticles of resistant and susceptible engorged female ticks showed significant increases in red autofluorescence at sites immediately under fungal hyphae. This is the first report 1) of tick mortality occurring after cuticle penetration but prior to hemocoel colonization and 2) that resistant ticks are capable of killing Metarhizium after conidial germination on the outer surface of the cuticle.