Attached
Ips grandicollis (Eichhoff) is an inhabitant of the
subcortical tissues of coniferous trees, mainly Pinus species.
It has been classed as a pest of secondary importance, with the
potential to become a primary pest under outbreak situations,
both in its native habitat in North America and in South and
Western Australia (where it became established in about 1943).
Investigations carried out during this study have been
restricted to its major host species in Australia; Pinus radiata
D. Don. Factors which contribute to resistance of individual
trees to attack by.! .. grandicollis were investigated. The
defense mechanism usually involves the flow of resin from
reservoirs and ducts damaged by beetles during initial boring.
Failure to encounter any of these resin barriers, cessation of
boring and retreat ~as associated with secondary resin produced
by the damaged phloem cells. The absence of such defence
mechanisms in declining trees, resulted in continued boring.
During Dispersal, !. grandicollis was found to land randomly
on trees within a pine stand, the actual selection being made
after boring into the bark of the tree.
Dispersing adult !. grandicollis, either caught on pheromonebaited traps in the field or collected in the laboratory during
emergence from field infested logs, incluc1ed a high percentage of
mated females. Mating occurred only within galleries in the
bark. Some of the progeny adults, including siblings, mated before
emergence and later produced offspring. The number of females
(vi)
thus mated depended upon the time spent within the bark by
mature adults before emergence from the host in which they
developed. Virgin and mated females initiate galleries even in
the presence of male-initiated galleries. Moreover, males join
both virgin and mated females which have produced galleries.
Similarly, both virgin and mated females were accepted into
nuptial chambers by males.
A technique using GC/MS was developed to determine the
concentration of ipsenol in extracts of ••hole beetles.
Production of ipsenol in males began about 9 to 12 hr after
boring into suitable host material and this tended to coincide
with the appearance of faecal pellets in the frass. Adult males
which rejected bore-sites in 'resistant' trees had not produced
ipsenol. These data indicate that males do not feed and hence
do not produce any ipsenol until L~e decision to continue
boring has been made. This evidence supports the generally
accepted concepts of ipsenol production and its dependence on
feeding by the male, but it provides a more critical basis for
the development of secondary attraction of I. grwldicollis than
has so far been presented.
