Abstract
Ips acuminatus (Gyllenhall) andTomicus piniperda (L.) were the main scolytid beetles in Scots pine,Pinus sylvestris L., outbreak areas near Orleans, France during 1978-1979.Ips acuminatus attacked thin-bark logs whileT. piniperda attacked thick-bark logs. More than 150 species of insects were associated with these scolytids. Forty-five species (31 predators and 14 parasitoids) were confirmed as natural enemies of bark beetles. Three predators were abundant:Thanasimus formicarius L. (Col.: Cleridae),Rhizophagus depressus (F.) (Col.: Rhizophagidae) andMedetera spp. (Dipt.: Dolichopodidae). The first two were especially frequent in galleries ofT. piniperda, whileMedetera spp. were more abundant in galleries ofI. acuminatus. The main parasitoids wereRhopalicus tutela (Walker) andR. brevicornis Thomson (Hym.: Pteromalidae),Coeloides abdominalis Zetterstedt andC. melanostigma Strand,Dendrosoter middendorfi Ratzeburg andD. hartigii Ratzeburg, andSpathius rubidus Rossi (Hym.: Braconidae). These parasitoids are polyphagous. However,C. abdominalis was obtained fromT. piniperda but not fromI. acuminatus, while 5.rubidus andD. hartigii were obtained fromI. acuminatus but not fromT. piniperda. Temporal and relative abundance of natural enemies ofT. piniperda andI. acuminatus were studied. The predatorsR. depressus andT. formicarius had complementary limiting effects on bark beetles as adults and larvae ofR. depressus fed mainly on scolytid eggs, whileT. formicarius adults attacked scolytid adults and the clerid larvae preyed upon scolytid larvae. The predatory pressure applied byT. formicarius andR. depressus toT. piniperda early during the spring was later complemented by a series of parasitoids and other predators. This sequential timing of the natural enemies ofT. piniperda suggests that the interactions among the guild are more complementary than adverse. Differential timing of the natural enemies in logs infested byI. acuminatus and some evidence of competition between the predatorsMedetera spp. and parasitoids suggested a less effective control of this scolytid.
Published Version
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