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Feeding Amount And Digestive Enzymes And Tree Decomposition Of Three Species Of Xylophagous Insects

Posted on:2008-12-27Degree:MasterType:Thesis
Country:ChinaCandidate:J M WangFull Text:PDF
GTID:2143360215486783Subject:Forest protection
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Both the impact on forest ecosystem and the loss of host forest are very large whenxylophagous insects outbreak. Former researchers have done some research work about harmsand risk analyses of xylophagous insects, however, none research papers of generally andsystematically analyzing the loss of host forest induced by xylophagous insects were reported.In this paper, loss of host forest induced by three species of xylophagousinsects—Monochamus alternatus, Tomicus piniperda and Pissodes punctatus—were analyzedand explained through three different angles: feeding amount, digestive physiology andcomparison of biochemical components between food and excrement of the insect. The lossstudied in the paper included losing biomass, microcosmic physical makeup of losing part,losing proportion and realistic decomposition degree of different materials, etc.The results of studying losing biomass of host forest induced by three insects revealed thatindividuals of Monochamus alternatus can cause the biggest loss of biomass in all of them:feeding amount of larva presented as exponential growth approximately. Mean total feedingamount of a larva(1 to 4 instar )can reach 24.40cm3. Adult daily mean feeding amount reached305.74 mm3 and mean total feeding amount were 25.28cm3. Larvae of P. punctatus can causebigger loss of biomass than that of T. piniperda, however, the opposite result was found inadults. Mean total feeding amount of larva(1 to 4 instar) of T. piniperda was about 0.29cm3,and 0.89cm3 for adult(90d). Mean total feeding amount of larva(1 to 4 instar) of P. punctatuswas about 0.37cm3, and 1.64cm3 for adult(360d).The results of microcosmic physical makeup and proportion of losing part revealed thatthere were 2 losing parts which formed forest loss—mineral elements and organic ones. In themineral elements' part, general loss of metallic elements was greater than solid non-metallicones. In the organic elements' part, loss of pectin, raw fibre(included cellulose, hemicelluloseand lignin, etc.), starch, raw fat and gross sugar were greater.The results of realistic decomposition degree of different materials of losing part revealedthat simple homogeneous polysaccharides as pectin, starch and fibre substances(includedcellulose and hemicellulose)were the main source of nutrition of xylophagous insects, and also were the main parts of host forests decomposed by xylophagous insects. There were 10digestive enzymes in larvae of Monochamus alternatus, the activity order arranged as pectinase>amylase>endo-β-1, 4-glucanase (Cx-ase)>hemicellulase>invertase>β-1, 4-glucosidase>exo-β-1, 4-glucanase (C1-ase)>lipase>trypsinlike enzyme>pepsin(8 digestive enzymeswere detected in adults, the activity order arranged as pectinase>amylase>hemicellulase>invertase>Cx-ase>C1-ase>lipase>trypsinlike enzyme); there were 8 digestive enzymes inTomicus piniperda and 6 in Pissodes punctatus, the activity order of Tomicus piniperdaarranged as pectinase>amylase>hemicellulase>invertase>C1-ase>trypsinlike enzyme>lipase>pepsin, and pectinase>amylase>Cx-ase>hemicellulase>invertase>C1-ase forlarvae and pectinase>amylase>hemicellulase>Cx-ase>invertase>C1-ase for adults ofPissodes punctatus. Nearly half of real digestion and utilization of food uptaked by threespecies of insects were pectin. The result pectinase has the highest activity under 55℃andpH=8.6. Pectinase had Michaelis constant Km=3.75 and Vmax=12500. The capability order ofthree species of insects decomposing fibre substances arranged as M. alternatus>P. punctatus>T. piniperda. Losing raw fibre of forest induced by larva stage of a M. alternatus was3782mm3, however, the real quantity of decomposition and consumption was 902.80mm3.Losing raw fat of forest induced by larva stage ofa T. piniperda was 9.95mm3, the real quantityof decomposition and consumption was 7.98mm3.
Keywords/Search Tags:xylophagous insect, Monochamus alternatus, Tomicus piniperda, Pissodes punctatus, feeding amount, digestive enzyme, tree decomposition
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