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Preliminary studies on the efficacy and establishment ofRoptrocerus xylophagorum [Hym.: Torymidae], a parasitoid ofIps grandicollis [Col.: Scolytidae], in Australia
Authors:P R Samson  J Smibert
Institution:(1) Deparment of Entomology, Waite Agricultural Research Institute, 5064 Glen Osmond, S.A., Australia;(2) Present address: Entomology Branch, Department of Primary Industries, Meiers Road, 4068 Indooroopilly, Qld, Australia
Abstract:Parasitization ofIps grandicollis Eichhoff byRoptrocerus xylophagorum (Ratzeburg), and intra-specific competition withinIps broods, were studied under laboratory conditions. Largest numbers of immatureR. xylophagorum were found in logs sampled when about half theIps brood were callow adults. Rates of parasitization rarely exceeded 20 %, and were usually much lower. Numbers of parasitoids were not affected by bark thickness. In the absence of parasitism,Ips broods suffered a density-dependent mortality which increased greatly in intensity and continued to act later in development of the broods when initial densities of larvae exceeded a threshold of about 400 per 1 000 cm2 of bark. The possible significance of this mortality is discussed in relation to the ability of parasitoids to reduceIps numbers. A field experiment was done to investigate the ability ofR. xylophagorum to establish in a new habitat. Populations were established for 1 or more generations by releasing 50 females at sites prepared by supplying small numbers of logs containing immatureIps.
Keywords:Roptrocerus xylophagorum                      Ips grandicollis            scolytid population dynamics  scolytid biological control  parasitoid efficacy
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