The Roles Of Serratia Infection Related With Resistance To Pathogenic Bacteria In Aphis Gossypii Glover

There are obligate symbionts and facultative symbionts in insects,obligate symbionts are mutualists that play some essential role,typically synthesizing nutrients missing from the insect’s diet,and facultative symbionts have more diverse effects,which range from parasitism to mutualism.Presently,the capacity of symbionts as defenders of their hosts has received more and more attentions,investigations from a range of endosymbionts indicated that some symbionts can protect their host against viruses,fungi in insect pests.However,the protection against bacteria is still unknown.This paper aimed to study the association of symbionts with resistance to pathogenic bacteria and explore new roles of symbionts in insects.The symbiont infection in Aphis gossypii Glover collected from field cucumber and pumpkin in Nanjing was compared by molecular biological detection method,the susceptibility to Serratia marcescens in A.gossypii with different symbiont infection was determined by bioassay,and the impact of S.marcescens on the community structure of endosymbionts in aphids was detected by spraying treatment.(1)Infection characteristic of endosymbionts in A.gossypii from Nanjing The symbiont infection in A.gossypii Glover collected from field cucumber and pumpkin in Nanjing was compared by molecular biological detection method.The results showed that symbiont infection in A.gossypii varied with host plants,six symbionts including Buchnera,Arsenophonus,Wolbachia,Serratia,Spiroplasma and Rickettsia were present in aphids from cucumber,and Rickettsia was not found in all the tested individuals from pumpkin.The infection incidence of Wolbachia,Spiroplasma and Rickettsia in aphids from cucumber were higher than that from pumpkin.(2)Effects of antibiotics on endosymbionts in A.gossypii To remove symbionts,aphids were fed on leavers treated with antibotics.The results showed that Spiroplasma in A.gossypii could be removed effectively by tetracycline,Arsenophonus and Serratia could be removed effectively by ampicillin,Arsenophonus was more sensitive to ampicillin than Serratia.(3)Effects of endosymbionts on susceptibility to Serratia marcescens in A.gossypii The susceptibility to Serratia marcescens in A.gossypii with different symbiont infection from cucumber and pumpkin was compared.The results showed that aphids collected from field cucumber harboring Arsenophonus,Wolbachia,Serratia,Spiroplasma and Rickettsia were more resistant to S.marcescens than that harboring Arsenophonus,Wolbachia,Spiroplasma and Rickettsia,and aphids collected from field pumpkin harboring Serratia were also more resistant to S.marcescens than that without Serratia.This indicated that Serratia in A.gossypii has association with the improvement of resistance to S.marcescens(4)Fluctuation of Serratia infection rate in A.gossypii under successive selection of S.marcescens and successive selection with S.marcescens did not affect the population trend index of A.gossypii.So there was significant difference in symbiont infection in A.gossypii collected from field cucumber and pumpkin in Nanjing,and the symbiotic bacteria Serratia has relation with improving its hosts’ resistance to the pathogenic bacteria S.marcescens.,the pathogenic bacteria resulted in an increase of Serratia infection in the host population...