Host selection behavior of the Douglas-fir pitch moth, Synanthedon novaroensis (Hy. Edwards) (Lepidoptera:Sesiidae), related to intermediate silvicultural activities

Abstract

The Douglas-fir pitch moth (DFPM), Synanthedon novaroensis, is attracted to exudations of oleoresin and oviposits at wounds on the bole of host trees. Larvae then feed in subcortical regions of vigourously growing hosts. With the increase use of pruning in young stands of Douglas-fir, Pseudotsuga menzesii (Mirb.) Franco, the potential exists for the DFPM, attracted to pruning wounds, to create defects that would reduce the value of wood products and erode potential returns on this investment. Therefore, the objective of this study was to investigate the relationship between host selection behavior of the DFPM related to intermediate silvicultural activities such as pruning. Specific objectives of this study were to determine if DFPM demonstrates an ovipositional preference between: individual pruned Douglas-fir trees; clones of Douglas-fir; branch pruning wounds and wounds on the bole of Douglas-fir; pruning wounds made through the branch collar and wounds made outside the branch collar; and wounds made during different seasons of the year.A series of field experiments were conducted in young Douglas-fir stands in Western Washington from 1991-1997. The principal conclusions from these experiments were: DFPM host preference varies significantly between individual Douglas-fir trees; DFPM host preference varies significantly between clones of Douglas-fir; DFPM oviposits at wounds on the bole of a host more often than at wounds made outside the branch collar; DFPM oviposits significantly more often at pruning wounds made through the branch collar than at pruning wounds made outside the branch collar; and DFPM oviposits significantly more often at pruning wounds made in the spring than at pruning wounds made in summer, autumn, or winter.