Abstract
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.
Highlights
Ticks are bloodsucking ectoparasites that can transmit pathogenic agents to humans and animals
Effect of Dopamine on the Survival of Ticks Treated with M. anisopliae
The group inoculated exclusively with the fungus (M) reached 17 ± 7% tick survival 72 hpi, while ticks injected with both DA and M. anisopliae (DM) exhibited 67 ± 13%
Summary
Ticks are bloodsucking ectoparasites that can transmit pathogenic agents to humans and animals. The southern cattle tick Rhipicephalus microplus (Acari: Ixodidae) is considered a major concern for livestock producers in tropical areas. This tick causes economical losses estimated at 3.24 billion dollars per year only in Brazil [1]. These losses are due to cattle mortality, the lower market value of leather, and reduced weight gain, milk, and meat production [2,3]. The inappropriate use of synthetic acaricides increases concerns about human and environmental health and advances the selection of resistant tick populations [4,5]. The use of entomopathogenic fungi to control ticks, Metarhizium (Hypocreales: Clavicipitaceae) and Beauveria (Hypocreales: Cordycipitaceae), has high potential [6,7,8,9,10,11]
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