[Parasitism of Ips sexdentatus (Insecta: Scolytidae) by Parasitorhabditis ipsophila (Nematoda: Rhabditidae)].

The study of parasitism percentages and contaminations intensity in Ips sexdentatus parasitized by P. ipsophila as well as the examination of the wormholes in the galleries of the bark beetle gave better insight into certain features of nematode biology. Larvae of I. sexdentatus could be infected, whereas pupae could not. Adults were contaminated from initial stages of maturation and throughout preswarming maturation. Following swarming and installation on a new tree, insects were rapidly decontaminated, but recontamination could occur by the end of oviposition. P. ipsophila larvae were found in the mesenteron before they penetrated into the hind gut. Seemingly, the parasite underwent no evolution within its host. All developmental stages of the nematode could be observed in the galleries of the bark beetle as long as the latter was present. No apparent relation exists between parasitism of the digestive tract by P. ipsophila and parasitism of the body or fat body by Parasitaphelenchus or Contortylenchus diplogaster. P. ipsophila exerts very limited effects on I. sexdentatus populations. A slight delay in swarming and initiation of oviposition, and a very low decrease in density of notches of oviposition and of eggs was observed, but the features of the gallery of oviposition (total length, length before the first notch) showed no alteration. No mortality was detected.