Studies On Biological Control Of Monochamus Alternatus Hope By Using Insect Natural Enemies

The pine wood nematode, Bursaphelenchus xylophilus, is transmitted by Monochamusalternatus Hope (Coleoptera: Cerambycidae), which are not only the primary vector of B.xylophilus in China but also the important woodborers of native coniferous forests．To explorethe non-pubic hazard sustained way to control the pine sawyer, M. alternatus, the study onbiological control of M. alternatus by using insect natural enemies was carried out by author.These findings may serve as reference for establishment of technical criterions for naturalenemy release in forests and rational evaluation on the ability of natural enemies against thepest in fields.1. Study on breeding three species of Sclerodermus (Hymenoptera: Bethylidae) specieswith larvae of M. alternatus. The lethality rate, parasitism rate and mortality of hosts ofSclerodermus sp1. were75.56%,61.11%and90%respectively, were better than Sclerodermussp2. and S. guani in same conditions. Offspring's number per tube of the three bethylid specieswere81.38,52.05and73.71, were comparatively accordant and the difference is notsignificant(df=2,89, F=3.009, P=0.0545). The main factors effecting offspring's number pertube was size of the host larvae. Offspring's total number of Sclerodermus sp. was2.84and1.58times better than Sclerodermus sp2. and S. guani respectively.2. Using two species of Sclerodermus parasitoids to control the young larvae of M.alternatus was studied. Laboratory experiment indicated that Sclerodermus sp. could kill95.7%of the1st instar larvae,85.9%of the2nd instar larvae, and57.9%of the3rd instar larvaof the pine sawyer by stinging and host-feeding. In addition, the parasitoid completed ageneration on the2nd-3rd instar host larvae(parasitism); Parasitism rates of two species ofSclerodermus to M. alternatus young larvae increased with the increase of parasitoid density.However, the maximum parasitism rate of Sclerodermus sp. could be up to60%in the lab, wasmuch higher than S. guani. And the periods to control M. alternatus larvae using Sclerodermussp. were in the year after the eggs hatched and before3rd inster larvae stage. 3. Control rate of Sclerodermus sp. on the young larvae of M. alternatus. The response ofthis parasitoid to its host, in field and indoor mesh, was shown to be highly variable andunpredictable and between2%and15%of all parasitioids released entered a target pinesawyer-infested cutlog. The parasitoid did not respond differently to aggregations of1,3, or6pine sawyer-infested cutlogs. However, the performance of Sclerodermus sp. released ascarrying immature eggs of parasitized hosts was up to five times approximately better thanwhen the parasitoid was released as carrying mature eggs. Individual performance was, a singleparasitoid killed, on average, by a combination of host-feeding and parasitism, between2.1and7.7individual larva of the pine sawyer.4. Bio-control of M. alternatus by releasing eggs and adults of the parasitoid D.helophoroides. The parasitoid respond differently to DBH of5-8cm,10-15cm, or>18cmpine sawyer-infested cutlogs. The highest parasitism rate was72.41%in DBH of5-8cmcutlogs, significant difference between else(releasing eggs:df=2,8, F=25.947, P=0.0011；releasing adults:df=2,8, F=28.556, P=0.0009). During three periods(May, July, September) ofreleasing the parasitoid respectively, the parasitism rates of the pine sawyer larvae orderly were68.50%,21.63%and30.29%, May period was the best(releasing eggs:df=2,8, F=41.297,P=0.0003；releasing adults:df=2,8, F=17.608, P=0.0031).Among three plots of releasing theparasitoid eggs, the mean correction reducing rate of the pine sawyer larvae per tree was48.54%, and the mean correction reducing rate of infested trees was63.07%. Among threeplots of releasing the parasitoid adults, mean correction reducing rate of the pine sawyer larvaeper tree was47.00%, and the mean correction reducing rate of infested trees was68.00%. Thecontrolling results by releasing adults of the parasitoid were a little better than releasing eggs ofthe parasitoid by comparing the controlling effect, however there was no significant differencebetween them.5. Assessment of control effectiveness of natural enemies (Sclerodermus sp. and D.helophoroides) on M. alternatus by life table. Index of population trend of M. alternatus was1.09in biocontrol area, while6.95in CK area. The quantity of the second generation of M.alternatus in biocontrol area decreased to15.68percent of CK area. Results showed that the parasitoids(Sclerodermus sp. and D. helophoroides) are the dominant factors affecting thepopulation of M. alternatus.In this dissertation,the biology and ecology of Sclerodermus sp. and D. helophoroideswhich parasited on the M. alternatus, and releasing these natural enemies in field at differencedevelopment stages of M. alternatus, to control larvae and pupa of this pest, was studied. Baseon introduce biological factors—natural enemies of M. alternatus artificially into the forestecosystem, and combined with other biological factors in forest, to constructed the integratedmanagement techniques of M. alternatus mainly by biological control. Finally, population of M.alternatus was controled, and more important the spread and increase of pine wilt diseasecould be prevented effectively.