INFLUENCE OF SOME SCOTS PINE CLONES ON DI PRION-PINI L (HYM, DIPRIONIDAE) DEVELOPMENT - NOXIOUS EFFECT IN-FIELD

The study attempts to confirm in nature the noxious effect of some Sco ts pine clones from Polish origin on Diprion pini. Up to now, this nox iousness has only been proved in standard laboratory conditions by fee ding the insects with cut pine shoots. Because significant natural pop ulations were lacking during recent years, the first experiments were carried out in 1991, 1992 and 1993 with larvae issued from a permanent rearing strain of D pini. These larvae were transferred to tree colle ctions of Orleans and Cadouin in Dordogne (France) and put on several vegetative copies of different Scots pine clones. These tests encounte red many difficulties due to the weakness of the laboratory strain in natural climatic conditions, the lack of synchronization between reare d insect and natural insect generations, the natural parasites and the distance between the lab and Cadouin. On the other hand, the real apt itudes of the clones in situ may only be proved during a real outbreak of the sawfly. However, an earlier mortality and a slower development are clearly shown when the insects develop on clones previously noted as unfavorable to D pini in laboratory bioassays.