Bark beetle feeding behaviors and their interaction with forest pathogens.

摘要

Dissection of digestive tracts showed that five bark beetle species, Ips paraconfusus, Dendroctonus jeffreyi, Tomicus piniperda, Scolytus multistriatus , and Phloeosinus sequoiae, feed beneath the bark as callow adults prior to emergence from brood trees. Callow I. paraconfusus and D. jeffreyi were found to ingest food material once the cuticle became yellow, while callow T. piniperda and S. multistriatus did not feed until their cuticles were light brown and black, respectively. Callow adults that were allowed to feed survived longer and became darker-colored individuals more frequently than starved beetles.;In a sequential extraction (hexane, methanol, and water) of ponderosa pine phloem and subsequent assay on alpha-cellulose, methanol and water extractives elicited significant feeding in both sexes of I. paraconfusus. The four most common sugars present in ponderosa pine phloem (sucrose, glucose, fructose, and raffinose), two pine stilbenes (pinosylvin and pinosylvin methyl ether), and ferulic acid glucoside, did not stimulate or reduce feeding when assayed with or without stimulatory methanol extractives. The mean length of phloem in the digestive tracts of male I. paraconfusus was significantly lower in beetles confined to the basal sections of ponderosa pines artificially-inoculated with Heterobasidion annosum, compared to those in trees which were mock-inoculated or uninoculated and did not contain the pathogen.;Less than 2% of all asymptomatic or pitch canker-symptomatic Monterey pine branches with green foliage were colonized by twig beetles, Pityophthorus spp., while approximately 50% of branches with yellow and red foliage contained twig beetles. Overall phoresy rates of emerging insects were significantly higher at Pebble Beach than at Oakland. At both sites, there was considerable seasonal variation in the proportion of branches colonized by twig beetles, the mean number of emerging twig beetles, and the phoresy rates of emerging insects. Chipping of branches reduced the emergence of Pityophthorus spp. and associates by approximately 95%, compared to intact branches. The pathogen was frequently isolated from one-year-old branches and chips, but was recovered from three-year-old branches in only 1 of 46 sampled.