Answers are grounded in this paper and cite their sources.
Pityophthorus orarius Bright is a small beetle which mines and kills shoots of Douglas-fir. The adult tunnels into the shoot in early summer and lays its eggs. Tunnelling of the larvae causes twig mortality indicated by characteristic "flagging".
No takes yet. Share an insight, caveat, or question.
Hedlin et al. (1970) studied this question.
Synapse has enriched 10 related papers. Consider them for comparative context: