An Evaluation On Pathogenicity Of Beauveria Bassiana Against Psoroptes Ovis Var.Cuniculi

Psoroptic mange in rabbit is a contagious,chronic and infectious disease with a main clinical feature of paper roll-like scab forming in the external auditory canal caused by Psoroptes ovis var.cuniculi.This mange can lead the rabbits to death in severe cases and cause huge losses to the rabbit industry.Currently,the chemical insecticide is the main control method against P.ovis var.cuniculi,but problems including drug resistance and residues in the meat are increasingly prominent,thus,we hope to find a new,green and effective control method against the psoroptic mange now.Beauveria bassiana is a highly effective and environmentally friendly bioinsecticide widely used in the control of agricultural and forestry pests.Some studies have confirmed that the entomopathogenic fungus can infect P.ovis,however,there is a lack of systematic evaluation of its clinical efficacy against psoroptic mange.Therefore,this study intended to use commercially available powder of B.bassiana to analyze the pathogenicity against P.ovis var.cuniculi in vitro and in vivo.Furthermore,the mechanism of the pathogenicity was analyzed on mRNA,protein and tissue levels of mites.And the main findings were as follows:1.Evaluation of Beauveria bassiana pathogenicity against Psoroptes ovis var.cuniculiIn order to evaluate the effective pathogenicity of B.bassiana against P.ovis var.cuniculi,in this study,we used an impregnation method to evaluate four concentrations of B.bassiana?4.26×10⁹,4.26×10⁸,4.26×10⁷,4.26×10⁶ conidia/mL?against P.ovis var.cuniculi in vitro.And the best pathogenic concentration?4.26×10⁹ conidia/mL?was screened to treat the psoroptic mange in rabbits by spraying to evaluate the therapeutic in vivo,sterile water?spray?and ivermectin?injection?as negative and positive control,respectively.Test mites immersed with four concentrations of a B.bassiana suspension exhibited dose-and time-dependent susceptibility responses;applying 4.26×10⁹conidia/mL resulted in 100%mortality of P.ovis var.cuniculi within in a 9-day period,with an LT₅₀ of 2.65 days.In vivo,rabbits infected with P.ovis var.cuniculi that were treated with 4.26×10⁹ conidia/mL of the B.bassiana fungal suspension showed a 100%therapeutic effect 3 days later,an efficacy greater than that provided by the anti-parasite drug ivermectin?62.21%?.Moreover,all rabbits treated with B.bassiana and ivermectin did not show symptoms of disease recurrence until 30 days post-treatment.Taken together,these results show that B.bassiana has high efficacy against P.ovis var.cuniculi;hence,it may offer a potentially effective biological insecticide for use against psoroptic mange.2.A preliminary study on acaricidal mechanism against Psoroptes ovis var.cuniculi of Beauveria bassianaIn order to clarify the acaricidal mechanism of B.bassiana against P.ovis var.cuniculi.In this study,we used the impregnation method to deal with P.ovis var.cuniculi in vitro by 4.26×10⁹ conidia/mL of B.bassiana.And then we collected these mites of 1-2d after treatment for histopathological observation,as well as we collected these mites of 1-7d after treatment and determined the protein level of acetylcholinesterase?AchE?,glutathione-s-transferase?GSTs?,carboxylesterase?CarE?,superoxide dismutase?SOD?and peroxidase?POD?by 96 hole micromethod,futher,we also destroyed the mRNA transcriptional level of the 5 enzymes by qPCR method at the same time.The results showed that the structure of lumen of the intestine?LU?of P.ovis var.cuniculi was after the infection of B.bassiana both1d and 2d,moreover,the basement membrane?MB?and the peritrophic matrix?MP?were broken off and the intestinal content?CI?was vacuolated.Furthermore,the detection of microassay and qPCR showed that AchE and GSTs increased at first and then decreased,while SOD and POD decreased first and then increased,and there were significant changes compared with the control group over the same period.Therefore,the intestinal structure of P.ovis var.cuniculi is the most susceptible to the B.bassiana.Taken together,it is assumed that B.bassiana may affect the intestinal digestive system,motor nervous system and energy metabolism system of P.ovis var.cuniculi,resulting in the death of mites.