Ultrastructural and Cytotoxic Effects of Metarhizium robertsii Infection on Rhipicephalus microplus Hemocytes

Abstract

Metarhizium is an entomopathogenic fungus widely employed in the biological control of arthropods. Hemocytes present in the hemolymph of invertebrates are the cells involved in the immune response of arthropods. Despite this, knowledge about Rhipicephalus microplus hemocytes morphological aspects as well as their role in response to the fungal infection is scarce. The present study aimed to analyze the hemocytes of R. microplus females after Metarhizium robertsii infection, using light and electron microscopy approaches associated with the cytotoxicity evaluation. Five types of hemocytes (prohemocytes, spherulocytes, plasmatocytes, granulocytes, and oenocytoids) were described in the hemolymph of uninfected ticks, while only prohemocytes, granulocytes, and plasmatocytes were observed in fungus-infected tick females. Twenty-four hours after the fungal infection, only granulocytes and plasmatocytes were detected in the transmission electron microscopy analysis. Hemocytes from fungus-infected tick females showed several cytoplasmic vacuoles with different electron densities, and lipid droplets in close contact to low electron density vacuoles, as well as the formation of autophagosomes and subcellular material in different stages of degradation could also be observed. M. robertsii propagules were more toxic to tick hemocytes in the highest concentration tested (1.0 × 10 8 conidia mL −1 ). Interestingly, the lowest fungus concentration did not affect significantly the cell viability. Microanalysis showed that cells granules from fungus-infected and uninfected ticks had similar composition. This study addressed the first report of fungal cytotoxicity analyzing ultrastructural effects on hemocytes of R. microplus infected with entomopathogenic fungi. These results open new perspectives for the comprehension of ticks physiology and pathology, allowing the identification of new targets for the biological control.

Schizophyllum commune induced oxidative stress and immunosuppressive activity in Spodoptera litura

“…SOD catalyzes the dismutation of superoxide anion to hydrogen peroxide, which is subsequently detoxified to oxygen and water by catalase, ascorbate peroxidase or GST. Previous studies have demonstrated that, after fungal infection, protection systems of insects are activated to ward off infection and to maintain the normal physiological activities [38][39][40][41][42]. In our study, a significant increase in CAT, APOX and SOD activities were noticed in larvae of Spodoptera litura after treatment with ethyl acetate extract of Schizophyllum commune.…”

Metarhizium Anisopliae Challenges Immunity and Demography of Plutella xylostella

“…Hemocytes, upon invasion, play a vital role to defuse the pathogen activities by employing different biological processes such as phagocytosis and encapsulation [ 62 , 63 ]. Arthropods can produce various types of hemocytes depending upon the type of infection they face [ 64 ].…”

Comparative effectiveness of Metarhizium rileyi, novaluron, and glyphosate on immune system, development, and redox metabolism of Anticarsia gemmatalis

“…Interestingly, entomopathogenic fungi have a variety of mechanisms that can neutralize the host defenses, such as the production of secondary metabolites able to suppress the insect immune system (Dubovskiy et al, 2013). Fiorotti et al (2019) demonstrated that the entomopathogen Metarhizium robertsii negatively affected Rhipicephalus microplus tick hemocytes, probably causing cell death. De Paulo et al (2018), in the hemocyte quantifications performed after inoculation in M. robertsii and M. anisopliae, found notable changes in the number of hemocytes in R. microplus, with reduction of approximately 80% in females.…”