EFFECT OF THE FOLIAGE OF DIFFERENT PINE SPECIES ON THE DEVELOPMENT AND ON THE OVIPOSITION OF THE PINE SAWFLY DIPRION PINI L (HYM, DIPRIONIDAE) .2. INFLUENCE ON EGG-LAYING AND INTERSPECIFIC VARIABILITY OF SOME ACTIVE SECONDARY COMPOUNDS

This paper is concerned with an experiment dealing with the ovipositio n of female sawfly (D. pini L.) which were made to lay eggs on the twi gs of ten different species or sub-species of pine. These, inturn, had previously been tested for their foliage edibility by the sawfly. Sub sequent reference is made to a number of analyses of the chemical comp osition of the respective needles of the ten species. These analyses r efer solely to diterpene resin acids and a number of polyphenols belon ging to the flavonoid group which were suspected of being injurious to the sawfly. Black pine needles provide a suitable environment for the oviposition of the sawfly, and the female sawfly appears to lay even more eggs on this foliage than observed in Scots pine. Sawfly performa nce attained with P. radiata, P. banksiana, and P. contorta were also relatively consistant with results obtained on Scots pine, confirming that sawfly may constitute a real danger for species of North American origin. On the other hand P. pinaster and P. strobus foliage proved h ighly unfavourable to egg laying. LOW egg-laying performance was also observed on P. uncinata needles. The analyses reveal significant varia tions in the chemical composition of pine-host needles with respect to species, while no apparant correlation is evident with regards to saw fly development. Nevertheless, Scots pine, which appears to provide th e best food, contains fewer resin acids (abietanes and primaranes) tha n other species. Scots pine foliage is the richest in more polar compo unds, while being poor in abietic acid content. The latter is more abu ndant in P. pinaster, which contains mainly primarane acid. With regar ds to polyphenols, the two flavonoids (characterised as taxifolin and its glucoside, which are especially apparant in Scots pine clones noxi ous for the sawfly) were not found in the remaining nine species or su bspecies of pine. Furthermore, no clear relationships appears to exist between insect performance and the level of catechin content in folia ge in the respective species.