Intestinal Responses Of The Oriental Fruit Fly Bactrocera Dorsalis After Ingestion Of An Entomopathogenic Bacterium Strain

Bactrocera dorsalis(Hendel)is the main fruit fly pest of tropical and sub-tropical countries.The application of insecticides to manage this pest has led to serious resistance problems;therefore,new ways to control B.dorsalis are required.Pathogenic bacteria are sources of biocontrol agents for pest management.Here,we investigated the gut responses of B.dorsalis after ingestion of the entomopathogenic bacterium,Serratia marcescens PS-1,which was isolated from Phyllotreta striolata.Our findings provide new insights into the insect gut response to pathogenic bacterial invasion and may aid the development of new strategies for the biological control of B.dorsalis.The main findings were as follows:1.S.marcescens PS-1 is pathogenic to B.dorsalis adults,as oral ingestion of this strain induced approximately 90% mortality within 5 days.Histological analyses revealed that PS-1 damaged the intestinal epithelium.At 6 h post-infection(hpi),the epithelial cells of infected flies contained translucent vacuoles.At 12 hpi,epithelial cells from infected insects displayed abnormal microvilli compared with noninfected adults.The gut lumen was filled with bacteria and epithelial cells had been destroyed at 24 hpi.2.We generated a gut transcriptomic dataset using RNA-Seq at two time points(6 and24 h)after PS-1 infection.We found that genes encoding the peritrophic matrix constituent were down-regulated,while genes involved in lipid and glycan metabolism,and renewal of the gut epithelium,along with genes encoding digestive enzymes and stress response factors,were up-regulated.In addition,14 cecropin genes were identified and cloned from B.dorsalis.To our knowledge,the number of cecropins identified in the present study is greater than that reported in the insects of earlier studies.Moreover,some of the cecropins identified were significantly down-regulated after PS-1 treatment.