WOUND REACTIONS OF SCOTS PINE (PINUS-SYLVESTRIS L) TO ATTACKS BY TOMICUS-PINIPERDA L AND IPS-SEXDENTATUS BOERN (GAL, SCOLYTIDAE)

Bark beetles Tomicus piniperda and Ips sexdentatus were artificially i nserted in Scots pines. Attacks were also provoked in other trees by a ttractants. Resin how corresponding to each introduction was measured in the case of artificial insertions. In all cases, gallery length, re action zone length and the total quantity of induced resin contained i n the whole reaction were measured 5-6 weeks after insertions or attac ks. The attempt of gallery construction (beginning of gallery boring) and the beginning of oviposition were also noted in each case, as well as the presence of associated fungi. Resin flow discouraged T. pinipe rda, but not I. sexdentatus, to attempt a gallery construction. For th e two beetle species, however, it played no role after gallery boring had started. Although tree induced reaction was present during gallery elongation, at least in the case of T. piniperda, it was not clear if it played a role in stopping gallery elongation and in failure of ovi position. Few beetles were killed by resin flow or by tree reaction. T he existence of oviposition was not related to attack density, tree ch aracteristics or presence of fungi. Fungi were involved in the develop ment of the induced reaction in response to I. sexdentatus attacks, bu t not in response to T. piniperda attacks. When expressing reaction zo ne length or resin quantity as a function of gallery length, galleries where oviposition had begun were clearly separated from those where i t had not. For galleries where oviposition did not occur, reaction zon e length was always correlated with gallery length for T. piniperda, a nd not for I. sexdentatus, but in the latter case the correlations exi sted when considering only galleries without fungi. Accumulation of in duced resin was always correlated with gallery length for the two spec ies. Therefore, a tree's induced reaction is not basically a defense r eaction. The results corroborate the hypothesis that it is a wound rea ction induced by mechanical stress due to gallery boring, and amplifie d by fungi when they are effective. For T. piniperda, the beetle borin g activity seems to be the only way to exhaust tree response capacity.