Über das schädliche Auftreten der Diprion ‐ Arten ( Hym., Diprionidae ) in finnischen Kiefernbeständen in diesem Jahrhundert

Summary A report is given on the occurence of mass outbreaks of Diprion species in Finland between 1897–1962. Diprion sertifer appears locally at intervals from 5–6 years; heavy outbreaks occured with approximately 30 years intervals in 1897, 1932–33 and 1960–62. D. pini shows usually localised outbreaks, scattered over the whole country. There exists in both species an ecologically and climatically well definid centre of outbreaks, which is of larger extension in D. sertifer than in D. pini.