Articles by Martti Varama

The European Pine Sawfly (Neodiprion sertifer Geoffroy) is one of the most serious defoliators of Scots pine (Pinus sylvestris L.) in northern Europe. We studied the pattern in the regional occurrence of the outbreaks of N. sertifer in Finland in years 1961-90, and made predictions about the outbreak pattern to the year 2050 after predicted winter warming. We tested whether minimum winter temperatures and forest type and soil properties could explain the observed outbreak pattern. We analysed outbreak patterns at two different spatial levels: forest board- and municipal-level.

The proportion of coniferous forests on damage-susceptible soils (dry and infertile sites) explained a significant part of the variation in outbreak frequency at small spatial scale (municipalities) but not at large spatial scale (forest boards). At the forest board level, the incidence of minimum temperatures below -36 °C (= the critical value for egg mortality) explains 33% of the variation in the outbreak pattern, and at the municipal level the incidence of cold winters was also the most significant explaining variable in northern Finland. Egg mortality due to cold winters seems to be the most parsimonious factor explaining why there have been so few N. sertifer outbreaks in northern and north-eastern Finland. We predict that climate change (increased winter temperatures) may increase the frequency of outbreaks in eastern and northern Finland in the future.

• Virtanen, E-mail: tv@mm.unknown
• Neuvonen, E-mail: sn@mm.unknown
• Niemelä, E-mail: pn@mm.unknown
• Nikula, E-mail: an@mm.unknown
• Varama, E-mail: mv@mm.unknown

• Kurkela, Finnish Forest Research Institute, Vantaa Research Unit, P.O. Box 18, FI-01301 Vantaa, Finland E-mail: timo.kurkela@metla.fi
• Aalto, Finnish Forest Research Institute, Rovaniemi Research Unit, P.O. Box 16, FI-96301 Rovaniemi, Finland E-mail: ta@nn.fi
• Varama, Finnish Forest Research Institute, Vantaa Research Unit, P.O. Box 18, FI-01301 Vantaa, Finland E-mail: mv@nn.fi
• Jalkanen, Finnish Forest Research Institute, Rovaniemi Research Unit, P.O. Box 16, FI-96301 Rovaniemi, Finland E-mail: rj@nn.fi

• Annila, Finnish Forest Research Institute, P.O. Box 18, FIN-01301 Vantaa, Finland E-mail: erkki.annila@metla.fi
• Långström, Swedish University of Agricultural Sciences, Dept of Entomology, P. O. Box 7044, S-750 07 Uppsala, Sweden E-mail: bl@nn.fi
• Varama, Finnish Forest Research Institute, P.O. Box 18, FIN-01301 Vantaa, Finland E-mail: mv@nn.fi
• Hiukka, Finnish Forest Research Institute, P.O. Box 18, FIN-01301 Vantaa, Finland E-mail: rh@nn.fi
• Niemelä, University of Joensuu, Faculty of Forestry, P.O. Box 111, FIN-80101 Joensuu, Finland E-mail: pn@nn.fi

Unequivocal evidence on the antagonistic effects of endophytic fungi associated with woody plants against insect herbivores has been documented in only a few cases so far. Experimental evidence of the significance of needle endophytes to coniferous trees has remained scant because it is difficult to obtain trees with needles free of endophytes that could be used as comparable controls for trees infected with endophytes. Previously we reported a new methodology to get Norway spruce (Picea abies (L.)  Karst.) saplings without needle endophytes and to inoculate them with a needle endophyte Lophodermium piceae (Fuckel) Höhn. Here we describe the first trial where spruce saplings with and without needle endophytes were provided as substrate for insect larvae. We transferred larvae of two sawfly species, Neodiprion sertifer Geoffroy and Gilpina pallida Klug, to the seedlings. Even though the main host of these sawfly species is not Norway spruce, but Scots pine (Pinus sylvestris L.), they are also known to occasionally feed on spruce. In this experiment the larvae did not develop to pupae with the provided spruce substrate but consumed measurable amounts of needles. No significant difference was found between the extent of needles consumed by either of the two sawfly species in inoculated and uninoculated saplings.

• Müller, Natural Resources Institute Finland (Luke), Forest Health and Biodiversity, P.O. Box 2, 00791 Helsinki, Finland https://orcid.org/0000-0003-3699-2139 E-mail: micms.muller@gmail.com
• Hamberg, Natural Resources Institute Finland (Luke), Forest Health and Biodiversity, P.O. Box 2, 00791 Helsinki, Finland https://orcid.org/0000-0002-0009-7768 E-mail: leena.hamberg@luke.fi
• Varama, Natural Resources Institute Finland (Luke), Forest Health and Biodiversity, P.O. Box 2, 00791 Helsinki, Finland E-mail: martti.varama@pp.inet.fi