CONSUMPTION OF APICAL BUDS AS A MECHANISM OF ALLEVIATING HOST-PLANT RESISTANCE FOR EPIRRITA-AUTUMNATA LARVAE

Epirrita autumnata (Lep. Geometridae) larvae are free-feeding folivore s, which also consume apical buds of mountain birch (Betula pubescens ssp. tortuosa). In spring they damage both swelling apical buds and un furling leaves, and, in mid-summer, apical bud initials enclosing leaf primordia for the following year. Previous studies have shown that re moval of dormant or swollen apical mountain birch buds in spring incre ases the size and resource status of leaves emerging from remaining bu ds, and such leaves may become a better qualify diet for herbivores. A ssuming that larval damage to apical buds results in a similar increas ed resource status, larvae have a potential to increase the susceptibi lity of mountain birch leaves either rapidly, during the same season, or in a delayed manner, due to damage to buds of the following year. O ur experiments showed that experimental damage to bursting buds in spr ing did not lead to an induced susceptibility of leaves in the same se ason, but mid-summer damage to apical winter bud initials significantl y interacted with simultaneous defoliation, alleviating the delayed in ducible resistance of birches in the following year. However, compared to undefoliated control trees, no overall increase in susceptibility of foliage was observed. Thus, delayed amelioration due to consumption of apical buds may prolong E, autumnata outbreaks, but the absence of overall ameliorative effects suggests that bud consumption only does not contribute to the increase in density. Effects of debudding signif icantly varied among trees, and, for unknown reasons, larvae in experi ments consumed apical bud initials only at certain sites and in certai n trees. Sources of these variations have to be elucidated to be able to further generalize our results.