OPHIOSTOMATOID FUNGI ASSOCIATED WITH THE LARCH BARK BEETLE IPS CEMBRAE IN CENTRAL EUROPE AND IN SCOTLAND
T KIRISITS 1, MJ WINGFIELD 2 and DB REDFERN 3
1 Institute of Forest Entomology, Forest Pathology and Forest Protection, Universität für Bodenkultur Wien, Hasenauerstraße 38, A-1190 Vienna, Austria; 2 Department of Microbiology and Biochemistry, University of the Orange Free State, Bloemfontein 9300, P. O. Box 339, South Africa; 3 Forest Research, Northern Research Station, Roslin, Midlothian EH 25 9SY, United Kingdom
Background and objectives
The larch bark beetle Ips cembrae is associated with various larch species (Larix spp.) in Europe and Asia. It was introduced into Scotland from continental Europe and was first recorded there in 1955. In the natural range of European larch (Larix decidua) I. cembrae is regarded as a secondary pest, usually infesting recently cut logs or weakened trees. However, it can cause serious damage in larch plantations outside its natural distribution. Like most bark beetle species I. cembrae acts as a vector for blue-stain fungi, some of which are suspected of helping to overwhelm the defense mechanism of the host tree. In Scotland, Ceratocystis laricicola has been described as an associate of I. cembrae . This Ceratocystis species kills bark and seems to contribute to dieback and death of larch . The aim of this study was to compare the fungal flora of I. cembrae in Central Europe and in Scotland.
Materials and methods
In order to get a comprehensive view of the ophiostomatoid fungi associated with this insect, isolations were made from adult beetles, larvae, pupae, from discoloured wood as well as from ascospores and conidia obtained from perithecia and asexual stages of the fungi sporulating in the beetle galleries. In 1997 the ophiostomatoid fungi associated with I. cembrae were investigated at various localities in Scotland by isolating from ascospores and conidia obtained from sexual and asexual stages occurring in galleries made by the insect in logs and windblown trees. Malt extract agar (2 %) supplemented with 100 mgl-1 streptomycin sulphate was used as the medium for isolations. Occasionally, 100 mgl-1 of cycloheximide was added.
Results and conclusions
Six species of ophiostomatoid fungi were found to be associated with Ips cembrae. These included Ceratocystiopsis minuta, Ceratocystiopsis sp., Ceratocystis laricicola, Ophiostoma brunneo-ciliatum, O. piceae and a Graphium species which is cycloheximide sensitive and thus appears to be unrelated to anamorphs of Ophiostoma. Based on frequency of occurrence, C. laricicola, O. brunneo-ciliatum and Graphium sp. appear to be the dominant associates of the insect both in Scotland and Austria. There were qualitative and quantitative differences in the species isolated from beetles, larvae, pupae, stained wood and from ascospores and conidia obtained from fungal stages occurring in the insect galleries. C. laricicola was rarely isolated from the insects but it was the dominant species in stained wood. Furthermore, it seems to be the primary invader of larch sapwood following attack by Ips cembrae, succeeded by O. brunneo-ciliatum and Graphium sp.. O. brunneo-ciliatum was the species most frequently obtained when isolations were made directly from the insects. The mycoflora of I. cembrae in Europe and in Japan share similarities, but there are also significant differences . Besides Ips typographus and Dendroctonus rufipennis, I. cembrae is the only bark beetle species known to be constantly associated with a Ceratocystis species.
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2. Westhuizen KvD, Wingfield MJ, Yamaoka Y, Kemp GH, Crous PWJ, 1995. Mycological Research 99, 1334-1338.