Analysis On The Relationship Between The Difference Of Food Spectrum And Digestive Organs And Corresponding Enzymes In The Two Species Of Dioryctria Larvae(Lepidoptera:Pyralidae)

In Heilongjiang Province,the main pests endangering Pinus koraiensis and P.sylvestris var.mongolica are Dioryctria sylvestrella and D.abietella.The former endangers the cones,branches and trunk of P.koraiensis and the trunk of P.sylvestris var.mongolica,while the latter only endangers the cones of two hosts.In order to explore the relationship between the difference of food spectrum and digestive organs and corresponding enzymes in the two species of Dioryctria larvae,this study compared the structure of mouth organ and digestive tract of the two species of Dioryctria larvae,measured the contents of nutrients and secondary metabolites in P.koraiensis cones,branches and mixture of 2 mm deep xylem sapwood and phloem in the same area(hereinafter referred to as sapwood and phloem)of P.sylvestris var.mongolica trunk,and then compared and analyzed the enzyme activity data of digestive enzymes,detoxification enzymes and digestive enzymes of larvae feeding on corresponding host plant tissues.To explore the effects of nutrients and secondary metabolites in cones,shoots of P.koraiensis and sapwood and phloem of P.sylvestris var.mongolica trunk on the feeding choice of larvae.The main results are as follows:1.There are three obvious differences in the structure of mouthparts of two species of Dioryctria larvae: first,the spicule of the epipharynx of D.sylvestrella are more than that of D.abietella;Second,the number of incisors on the mandibular of D.sylvestrella than that on D.abietella;Third,the diameter of the spinneret bears an oriffis of D.sylvestrella are larger than that of D.abietella.The ultrastructural observation showed that the both of the two specices of Dioryctria have five kinds,sensilla trichomes,sensilla chaetica,sensilla basiconca,sensilla styloconica and sensillum digitiformium.There were two subtypes of sensilla trichomes,sensilla chaetica and sensilla styloconica,four subtypes of sensilla basiconca and only one subtype of sensillum digitiformium.There was no difference in the shape of sensilla trichomes and sensilla chaetica subtypes between the two,but there is a difference in length;The distribution position,shape and length of sensilla basiconca subtypes were different;There were significant differences in the length and width of sensilla styloconica between two species of Dioryctria larvae.2.The structure of the digestive tract of two species of Dioryctria larvae are similar.The digestive tract is composed of foregut,midgut and hindgut,and the midgut accounts for the largest proportion of the digestive tract.There is a cardiac valve between the foregut and midgut,and a pyloric valve between the midgut and hindgut.The foregut is divided into pharynx,esophagus,crop and proventriculus.It is hyaline membranous and has no structure of gastric cecum.There are backward growing thorns at the front of the esophagus,which can prevent food backflow.The hindgut consists of ileum,rectum and anus,without colon and rectal pad structure.There are monolayer epithelial cells in the foregut,which can grind food and temporarily store food;The midgut is muscular.The epithelial cell layer has columnar cells with dense microvilli on the top and tightly arranged goblet cells.The cytoplasm is rich in organelles,which plays an important role in food digestion and nutrient absorption.The hindgut contains a large number of muscle cells,which are more muscular than the foregut,and both have good contractility,so as to facilitate the accommodation and promotion of food.There are 6 Markov tubes in the front of the hindgut,and 3 on both sides of the gut.3.By measuring the difference of nutrient content of P.koraiensis cones,branches and sapwood and phloem of P.sylvestris var.mongolica trunk,combined with the data of different larval digestive enzymes feeding on Pinus koraiensis cones,branches and sapwood and phloem of P.sylvestris var.mongolica trunk,the relationship between feeding difference and corresponding enzymes of two species of Dioryctria larvae is clarified.The water content in the sapwood and phloem of P.sylvestris var.mongolica trunk and the branches of P.koraiensis is low,but the total sugar content is higher than that in the cones,indicating that the water has little or negative effect on the feeding choice of D.sylvestrella larvae,while the total sugar has a feeding induction effect of D.sylvestrella larvae.The D.sylvestrella larvae tend to eat host plants with high fat content.4.By measuring the difference of secondary metabolites content of P.koraiensis cones,branches and sapwood and phloem of P.sylvestris var.mongolica trunk,combined with the data of different larval detoxification enzymes and protective enzymes feeding on P.koraiensis cones,branches and sapwood and phloem of P.sylvestris var.mongolica trunk,the relationship between feeding difference and corresponding enzymes of two species of Dioryctria larvae is clarified.According to the data analysis,the synthesis of detoxification enzyme care in larvae is to resist the toxicity of two secondary metabolites of total phenols and flavonoids in host plants and improve the stress resistance of insects.The activities of detoxifying enzymes and protective enzymes of D.sylvestrella larvae feeding on different host plants can fluctuate with the content of secondary metabolites to resist the toxicity of secondary metabolites.Plant secondary metabolites had no avoidance and feeding effect on the larvae of D.sylvestrella.