Evolution of a new outbreak of Diprion pini L. in the south of the "Bassin parisien" I. Development of the gradation until 1982 and connection with environment factors

• Published in: Annales des sciences forestières Vol. 41; no. 4; pp. 375 - 404
• Main Authors: Geri, C, Goussard, F
• Format: Journal Article
• Language: French
• Published: 01.01.1984
• Subjects: Diprion pini; Diprionidae
• ISSN: 0003-4312

Following a new outbreak of Diprion pini L. in southern "Bassin parisien", a study was carried out for following insect populations evolution and for determining regulation factors. The record are constituted by regional surveys supported by simple infestation data, more detailed surveys at the large stand scale, observations of the evolution of every life cycle at the plot scale. The research is concerned basically by parasitism and diapause. This study confirms both factors are really "key factors" determining population evolution during all the outbreak phases: increasing, decreasing and latence. The outbreaks shifted from the South-West to the North-East, as was remarked during the earlier gradation. The newly established populations are poorly diapausing and escape from parasites. The relationships between attack intensity and structure and specific composition of forest environment are described. The results give us little hope of using sylvicultural means to establish stands better able to withstand sawfly outbreaks. Favouring black pine and diversifying tree species in the country may bring some for increasing resistance to diprion attacks.