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We conducted a series of comparisons between root-infected and asymptomatic trees for a range of parameters
associated with host susceptibility to I. pini - O. ips complexes. These comparisons included field assays at the whole tree or
controlled bait level, and laboratory assays involving application of controlled treatments. Both groups of assays involved
behavioral tests with I. pini, and tree physiological responses to simulated I. pini - O. ips attack. The results are summarized
in Table 2.
Behavioral assays evaluated three phases of scolytid orientation to host trees: initial landing, host entry, and gallery
formation (Wood 1972, Elkinton and Wood 1980, Raffa and Berryman 1982c, Raffa 1988). Arrival rates to baited traps did
not differ between stem phloem strips from root-infected or healthy trees, stems artificially infected with various fungi
associated with Red Pine Decline, or volatiles associated with various intensities of stress (Table 2). When male I. pini were
caged directly onto trees, however, the entry rates were 2.4 X higher on trees adjacent to the margin of dead trees than on
trees farther into the stand. Prior excavations had demonstrated high levels of root disease in the former group (Klepzig et al.
1991). Three conclusions can be drawn from these results: (1) beetles can detect changes in stem phloem physiology and
Table 2.wComponents of I. pini colonization of P. resinosa affected by prior infestation with root-colonizing insects and
fungi
Parameter Treatment Comparison Result
a. Initial landing Host stem tissue Rootinfested vs. healthy trees ns
Host stem tissue Fungal-infected vs. non-infected ns
stems (Oi, On, Lt)
Volatiles etOH, ct-pinene, EtOH & tx-pinene, ns
vs. controls
b. Host entry Caging onto whole trees Root infected vs. healthy trees Prefer diseased trees: 7.X
c. Gallery formation Phloem strips Root weevil infected vs. healthy Prefer infested logs: 2.4X
logs
Amended phloem Nonpolai" extracts from constitu- Prefer healthy trees: 10X
tive stem phloem of rootinfected
vs. healthy trees
Amended phloem Nonpolar extracts from reaction Prefer diseased trees: 3.0X
stem phloem of root-infected
vs. healthy trees
Amended phloem Monoterpene contents present Prefer diseased trees: 3.5X
in reaction stem phloem of
root-infected vs. healthy trees
d. Constitutive resin Resin flow Stem phloem of root-infected ns
vs. healthy trees: 1.5m height
Stem phloem of root-infected Higher in healthy trees: 4X
vs. healthy trees: 10m height
e. Reaction resin a-pinene Root diseased vs. healthy trees Higher in healthy trees: 1.3X
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Data from Klepzig et al. (in prep.), Raffa and Smalley (in prep.).