Influence of cell viability of freshly felled Pinuselliottii on the subcortical community associated with Ipsgrandicollis (Coleoptera: Scolytidae)

Abstract

The influence of living host cells in billets from freshly felled Pinuselliottii Engelm. on the development of Ipsgrandicollis (Eichhoff) brood and the associated gallery organisms was determined. Billets were either left untreated or fumigated with methyl bromide to kill cells in the cambium and outer sapwood prior to exposure to I. grandicollis. Cell viability was monitored with triphenyltetrazolium chloride. Both species composition and abundance of the mycoflora within the larval galleries differed between the fumigated and control billets. Abundance of the two most common species in the controls, Ophiostomaips (Rumb.) Nannf., a phytopathogenic blue-staining fungus, and its anamorph, Graphilbum sp., was reduced in the fumigated billets. This appeared to relate to the increased presence of saprophytic nonstaining fungi, usually not observed in I. grandicollis galleries until completion of the beetle life cycle. This altered fungal species composition had a detrimental effect on both the I. grandicollis brood and the associated mites and nematodes. Fumigation possibly provided a competitive advantage to the saprophytic fungi by eliminating localized host cellular responses, which normally retarded their development. Domination by this different suite of mycoflora apparently altered the establishment and development of I. grandicollis brood by accelerating the decay processes.