The aim of the present study was to analyze ten native Metarhizium spp. isolates as to their UV‐B tolerances. Comparisons included: different fungal propagules (conidia, blastospores, or microsclerotia [MS]); conidia in aqueous suspensions or in 10% mineral oil‐in‐water emulsions; and conidia mixed with different types of soil. The UV‐B effect was expressed as the germination of conidia or culturability of blastospores and MS relative to nongerminated propagules. Metarhizium anisopliae LCM S05 exhibited high tolerance as blastospores and/or MS, but not as conidia; LCM S10 and LCM S08 had positive results with MS or conidia but not blastospores. The formulations with 10% mineral oil did not always protect Metarhizium conidia against UV‐B. Conidia of LCM S07, LCM S08, and LCM S10 exhibited the best results when in aqueous suspensions, 24 h after UV‐B exposure. In general, conidia mixed with soil and exposed to UV‐B yielded similar number of colony forming units as conidia from unexposed soil, regardless the soil type. It was not possible to predict which type of propagule would be the most UV‐B tolerant for each fungal isolate; in conclusion, many formulations and propagule types should be investigated early in the development of new fungal biocontrol products.

Background: Ticks are obligate bloodsucking parasites responsible for significant economic losses and concerns with human and animal health, mainly due to the transmission of pathogens. Entomopathogenic fungi have been intensively studied as an alternative strategy for tick control that can be used in combination with synthetic acaricides in the integrated management of ticks. Here, we investigated how the gut bacterial community of Rhipicephalus microplus is shaped after Metarhizium anisopliae treatment and how the tick susceptibility to the fungus is affected after disrupting gut bacterial microbiota. Methods: Partially engorged tick females were artificially fed with pure bovine blood or blood plus tetracycline. Two other groups received the same diet and were topically treated with M. anisopliae. The guts were dissected, and the genomic DNA was extracted 3 days after the treatment; the V3–V4 variable region of the bacterial 16S rRNA gene was amplified. Results: The gut of ticks that received no antibiotic but were treated with M. anisopliae exhibited lower bacterial diversity and a higher occurrence of Coxiella species. The Simpson diversity index and Pielou equability coefficient were higher in the gut bacterial community when R. microplus were fed with tetracycline and fungus-treated. Ticks from fungus-treated groups (with or without tetracycline) exhibited lower survival than untreated females. Previous feeding of ticks with the antibiotic did not change their susceptibility to the fungus. Ehrlichia spp. were not detected in the gueated groups. Conclusions: These findings suggest that myco-acaricidal action would not be impacted if the calf hosting these ticks is under antibiotic therapy. Moreover, the hypothesis that entomopathogenic fungi can affect the bacterial community in the gut of R. microplus engorged females is endorsed by the fact that ticks exposed to M. anisopliae exhibited a dramatic reduction in bacterial diversity. This is the first report of an entomopathogenic fungus affecting the tick gut microbiota. Graphical

Dopamine (DA) is a biogenic monoamine reported to modulate insect hemocytes. Although the immune functions of DA are known in insects, there is a lack of knowledge of DA’s role in the immune system of ticks. The use of Metarhizium anisopliae has been considered for tick control, driving studies on the immune response of these arthropods challenged with fungi. The present study evaluated the effect of DA on the cellular immune response and survival of Rhipicephalus microplus inoculated with M. anisopliae blastospores. Exogenous DA increased both ticks’ survival 72 h after M. anisopliae inoculation and the number of circulating hemocytes compared to the control group, 24 h after the treatment. The phagocytic index of tick hemocytes challenged with M. anisopliae did not change upon injection of exogenous DA. Phenoloxidase activity in the hemolymph of ticks injected with DA and the fungus or exclusively with DA was higher than in untreated ticks or ticks inoculated with the fungus alone, 72 h after treatment. DA was detected in the hemocytes of fungus-treated and untreated ticks. Unveiling the cellular immune response in ticks challenged with entomopathogenic fungi is important to improve strategies for the biological control of these ectoparasites.

Dopamine modulates ticks and insect hemocytes and links these arthropods’ nervous and immune systems. For the first time, the present study analyzed the effect of a dopamine receptor antagonist on the survival, biological parameters, phagocytic index, and dopamine detection in the hemocytes of ticks challenged by Metarhizium anisopliae. The survival and egg production index of Rhipicephalus microplus were negatively impacted when ticks were inoculated with the antagonist and fungus. Five days after the treatment, the survival of ticks treated only with fungus was 2.2 times higher than ticks treated with the antagonist (highest concentration) and fungus. A reduction in the phagocytic index of hemocytes of 68.4% was observed in the group inoculated with the highest concentration of the antagonist and fungus compared to ticks treated only with fungus. No changes were detected in the R. microplus levels of intrahemocytic dopamine or hemocytic quantification. Our results support the hypothesis that dopamine is crucial for tick immune defense, changing the phagocytic capacity of hemocytes and the susceptibility of ticks to entomopathogenic fungi.