The recent gradation of the European pine sawfly Neodiprion sertifer in Carinthia (between Völkermarkt and Klagenfurt) started in 1995 in a total area of about 2500 ha. Meanwhile the infested area grew up to more than 5000 ha (about 400 ha of it heavily damaged). The infested pines (most of them Scots pines) grow in secondary stands (often mixed with spruce, larch, oak and beech) between 400 and 600m altitude.
The typical symptoms of older needle feeding by the Neodiprion larvae, which can be best seen during the second half of May, were observed first on older trees (60-100 years). In younger stands of Pinus sylvestris extensive damage on the needles were reported only in the following years.
This phenomenon is not typical for Neodiprion infestations in our country. The fox headed pine sawfly is known to be a pest of 20 to 30 years old pine afforestations and not of old trees.
The same area was already attacked by Neodiprion sertifer from 1960 to 1965. At that time N. sertifer was associated by Gilpinia pallida.
A very interesting fact is also the long duration of the gradation. N. sertifer outbreaks usually last 2-3 years, before the density drops to an uncritical level of less than 1-3% of the peak level. In the most cases the reason for the rapid break down of the gradation is the polyhedrosis-virus Borrelinavirus diprionis. But also parasitoids (cocoon parasitoids) reduce the sawfly population.
In order to get some information about the intensity of the sawfly-attack in the different parts of the infested area and to get data for making predictions about the expected attack in the following year, we tried to install a kind of monitoring system in 1997.