FOLIAGE EDIBILITY OF SCOTS PINE CLONES FOR DIPRION-PINI L (HYM., DIPRIONIDAE) .1. INFLUENCE OF THE CONSUMPTION OF NEEDLES OF DIFFERENT PINE CLONES ON THE DEVELOPMENT OF D-PINI

Foliage edibility of Scots pine clones of French and Polish origin (woodlands near Haguenau in Alsace and near Taborz in Mazury) is tested on the pine sawfly Diprion pini L. Feeding bioassays were first performed with larvae of the first instar, larval mortality being appreciated after 10 or 12 days of foliage feeding. These tests were realized in standard laboratory conditions (20-degrees-C, 16h30/7h30 photoperiod and 16-degrees-C, 15h/9h photoperiod) with the foliage of 27 clones selected according to morphological characteristics. These experiments enabled us to select 4 clones showing well differentiated capacities of edibility, to feed more aged larvae, from the 4th instar to cocoon spinning. Several biological characteristics as development rate, size, fecundity and diapause rate were then observed in addition to mortality on diprions fed with the foliage of these clones. This later test was carried out in natural conditions of temperature and photoperiod. The whole of these experiments shows that some clones are favourable or unfavourable to the sawfly survival and development. Unfavourable clones are mainly found in clone population of Taborz origin. In addition to high mortality, consumption of the needles of these pines induces decrease in foliage eating and deterioration of the physiological state of the surviving insects: decrease in size and in fecundity, changes in development and diapause rate. These effects are compared, by bioassays on aged larvae, to consumption incidence of the young needles.