Application Of Beauveria Bassiana In The Control Of Aedes Mosquito And Its Transmitted Diseases

Background:Mosquito is an important vector,which can spread a variety of diseases.Zika virus(ZIKV)is a mosquito-borne flavivirus in the Flaviviridae family,which has posed a big threat to public health worldwide.ZIKV is spread mostly by the bite of an infected Aedes mosquito(Ae.aegypti or Ae.albopictus).Because there is no efficient vaccine or treatment for ZIKV available to date,mosquito control via insecticides is still the most frequently and widely used control strategy.The entomopathogenic fungus Beauveria bassiana,an environmentally friendly biological insecticide,has been proven to have a killing effect on mosquitoes.The application of Beauveria bassiana in the control of Zika virus disease and the construction of recombinant Beauveria bassiana with high virulence to mosquitoes is of great significance to vector control and prevention for mosquito-borne diseases.Methods:Firstly,Beauveria bassiana was applied to the prevention and control of Zika virus disease.The female Ae.albopictus mosquitoes(4-7 days after emergence)were exposed to a single infection of fungus B.bassiana(single fungus,SF),a single infection of ZIKV(single virus,SV),coinfection with the fungus and virus(coinfection,CI),or infection with neither(control).The survival time,the length of the first gonotrophic cycle from sucking blood to laying eggs and the amount of laying eggs of all mosquitoes were observed and recorded.In addition,on the seventh day of mosquito infection,the mosquitoes that were still alive were killed,and the virus infection of midgut,head and salivary gland were detected by qRT-PCR.The vectorial capacity of ZIKV transmitted by two groups of mosquitoes was calculated by the Ross-MacDonald model.In addition,to improve the insecticidal efficacy of the entomopathogen B bassiana,the fungus was genetically modified to express the insect-specific scorpion neurotoxin AaIT and Bacillus thuringiensis toxin Cyt2Ba,respectively.The virulence of the recombinant B.bassiana strain and the wild type strain to Aedes adults and larvae were measured by bioassays.Results:To evaluate the potential of the entomopathogenic fungus B.bassiana for ZIKV vector control,we compared the vectorial capacity of Ae.albopictus females blood-fed with ZIKV with or without exposure to Beauveria bassiana.We found that the fungal infection significantly decreased the amount of ZIKV by 3.6-,12.3-and 7.8-fold in mosquito midguts,heads and salivary glands respectively.On the other hand,the median survival time and fecundity of fungus-infected mosquitoes were reduced by 84.2%and 39.8%in comparison to the non-fungus-infected mosquitoes.The length of the first gonotrophic cycle was increased by 15.3%because of fungal infection.In addition,the recombinant B.bassiana expressing scorpion neurotoxin AaIT(Bb-AaIT)or Bacillus thuringiensis toxin Cyt2ba(Bb-Cyt2ba)was successfully constructed.The exogenous toxin gene can be stably inherited,transcribed and expressed in the recombinant fungi.The virulence of these recombinant strains against adults and larvae of Aedes mosquitoes was significantly improved.In addition,Bb-Cyt2Ba infection resulted in a dramatic reduction in the fecundity of the target mosquitoes.Conclusion:The entomopathogenic fungus,B.bassiana,can not only kill mosquitoes effectively,but also inhibit the replication of ZIKV in mosquitoes.In addition,recombinant B.bassiana genetically modified to express the insect-specific toxin AaIT or Cyt2Ba had higher virulence to adult and larva of Aedes mosquito.Thus,B bassiana,as a safe and effective biological insecticide,has a strong development and application value.