Tarmo Virtanen, Seppo Neuvonen, Pekka Niemelä, Ari Nikula, Martti Varama. (1996). Climate change and the risks of Neodiprion sertifer outbreaks on Scots pine. Silva Fennica vol. 30 no. 2–3 article id 5584. https://doi.org/10.14214/sf.a9229

Keywords: Pinus sylvestris; climate change; GIS; Neodiprion sertifer; cold tolerance; winter temperatures; insect outbreaks

Abstract | View details | Full text in PDF | Author Info

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

Category : Research article

article id 360, category Research article

Timo Kurkela, Tarmo Aalto, Martti Varama, Risto Jalkanen. (2005). Defoliation by the common pine sawfly (Diprion pini) and subsequent growth reduction in Scots pine: a retrospective approach. Silva Fennica vol. 39 no. 4 article id 360. https://doi.org/10.14214/sf.360

Keywords: height growth; NTM; defoliation; insect attack; needle density; needle production; needle retention; radial growth; herbivory

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The foliage status in the main stem of Scots pines (Pinus sylvestris) was studied retrospectively using the needle trace method (NTM) on a stand, seriously defoliated by the pine sawfly (Diprion pini) in the 1980s. Needle density increased abruptly in the seasons following the defoliation. The strongest reduction in annual needle production occurred one year later. As a consequence of lower needle production, the annual number of attached needles decreased three to five years after the defoliation. Needle retention and the average age of attached needles tended to increase after defoliation. In analyses of covariance with the NTM variables, needle density (logarithmic transformed values) and average age of attached needles, had the highest, significant, negative relationship with radial and height increments both in the period prior to the defoliation and in the time when the trees were suffering from defoliation. The relationships between height increment and the number of needles and needle loss were positive and significant. Also radial increment had a positive relationship with the number of needles but not with needle loss. Interestingly, an abrupt increase in the needle density gave a good indication of the effects of a sudden defoliation in pines.

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

article id 660, category Research article

Erkki Annila, Bo Långström, Martti Varama, Risto Hiukka, Pekka Niemelä. (1999). Susceptibility of defoliated Scots pine to spontaneous and induced attack by Tomicus piniperda and Tomicus minor. Silva Fennica vol. 33 no. 2 article id 660. https://doi.org/10.14214/sf.660

Keywords: Scots pine; defoliation; Scolytidae; Diprionidae; induced attack; Tomicus piniperda; Tomicus minor; Diprion pini

Abstract | View details | Full text in PDF | Author Info

In 1990–1991, Diprion pini extensively defoliated Scots pine (Pinus sylvestris L.) trees in Lauhanvuori National Park in southwestern Finland. Many trees lost all their foliage, while others had ca. 10% foliage left after the second year of defoliation. Outside the national park, many nearby stands were also heavily defoliated in 1990, but were sprayed with diflubenzuron (Dimilin®) in 1991. This protected the current year needles, corresponding to ca 30% of full foliage. In spring 1992, pine trees with 0, 10, 30 and 100% foliage remaining (10 small and 10 large trees in each category) were baited with pine bolts to induce stem attacks by pine shoot beetles. All baited trees were attacked by Tomicus piniperda and some by T. minor. The attacks failed in all these trees except those that were totally defoliated and some of the small trees with 10% foliage left. Many unbaited trees escaped attack entirely, but only totally defoliated trees were successfully colonized (i.e. produced brood). Attack densities and brood production figures peaked in baited, large and totally defoliated trees. None of the measures (cambial electrical resistance, resin flow, induced lesion length by fungal inoculation, amount of hydrocarbons or phenolic compounds) used to describe tree vigour at the time of attack gave better information than the estimated remaining foliage. We conclude that the risk for beetle-induced mortality following defoliation is a function of remaining needle biomass and beetle pressure. Even at high beetle densities (as was simulated by baiting of trees), trees with 10% of the foliage remaining were able to defend themselves against attacking pine shoot beetles.

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

Category : Research note

article id 23026, category Research note

Michael M. Müller, Leena Hamberg, Martti Varama. (2023). Palatability of Norway spruce needles infected with Lophodermium piceae to larvae of two sawfly species. Silva Fennica vol. 57 no. 3 article id 23026. https://doi.org/10.14214/sf.23026

Keywords: antagonism; herbivory; fungi; Neodiprion sertifer; Gilpinia pallida; palatability

Highlights: We describe the first experiment including both endophyte inhabited and endophyte free intact needles of Norway spruce for examining the possible effect of endophytes on the palatability of needles to insect larvae; The extent of needles consumed by neither of two sawfly species, Neodiprion sertifer and Gilpina pallida, differed depending on endophyte presence.

Abstract | Full text in HTML | Full text in PDF | Author Info

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

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