Page 4 - Volume 3, Issue 1, January 2010

© Benaki Phytopathological Institute
Karamaouna & Kontodimas 2
mainly resulting from the synergism of the
different terpenes contained in these plants
(12). Attraction of P. bicolor to Cupressaceae
(especially Cupressus, Juniperus, Thuja and
Callitris spp.) based on olfactory stimulus ex-
erted by the terpenes and sasquiterpenes
of these trees was proved in laboratory tri-
als using the olfactometer (10). Further tests
on the olfactive adaptation and allotrophy
of P. bicolor resulted in no feeding on an in-
habitual food-plant unless all the terpene
compounds were suppressed, in which case
the scolytid fed indiscriminately on wood of
any of the test tree species (11). In laboratory
bioassays, both sexes of the borer were at-
tracted to essential oils from the bark, xylem
and leaves (in descending order) of stressed
Platycladus orientalis (33).
Thin wind-broken branches or those dy-
ing from the cypress canker fungus Seiridium
cardinale (Wag.) Sutt. et Gibs. are commonly
infested during the endemic phase of P. bi-
color population. Well-developed, vigorous
trees after a sudden stress due to drought,
fire, root damage or heavy infection by S.
cardinale are preferred for breeding, where-
as suppressed trees are usually not attacked
(15, 25, 27). P. bicolor has been reported in
cypress plantations in Greece, being rath-
er rare (4), but it is known to cause serious
damage to nursery trees of Cupressaceae in
France and North Africa (18, Richard Thomp-
son, personal communication 2008). The sc-
olytid may also transmit the cypress canker
fungus, S. cardinale, in Cupressus, Juniperus
and Thuja (7, 16, 27, 32).
P. bicolor overwinters at both larval and
adult stage under the bark. In the Mediter-
ranean region adults emerge in late spring
or early summer and feed on twigs (6, 25).
Mating occurs in a chamber bored by the fe-
male. After mating, the pair tunnels under
the bark a brood chamber, which is at first a
short gallery around the entrance and then
it is extended along the grain of the wood.
Eggs are laid singly in chambers down both
sides of the central gallery. Larvae feed per-
pendicularly to the central egg gallery and
girdle the branch. The species completes 2
and 4 generations/year on Mediterranean
Cypress in Tunisia and Israel, respectively,
with extensive overlapping of generations
and 2-3 generations/year on Thuja trees in
China (6, 13, 15, 25).
Adults of P. bicolor feed on and may gir-
dle small twigs typically several inches back
from the tip for additional nourishment and
hibernation, causing discolored, dead tips
or “flags” hanging on the tree. Under an in-
tensive attack, the number of dead twigs is
very high (22). Excavation activity of galler-
ies occurs in early spring and summer and
ceases during winter. The gallery system
has a central tunnel running parallel to the
branch or trunk with numerous side tunnels
coming out of it at right angles (centipede-
like pattern). Trees subjected to attack weak-
en physiologically, grow less vigorously and
lose their ornamental appearance. There-
fore, the beetles contribute to the decline
and eventual death of the trees but they are
almost always not the primary cause (13, 22).
Natural enemies of P. bicolor com-
prise two predatory beetles, several para-
sitoid wasps and a parasitic mite primarily
recorded on Mediterranean Cypress in Is-
rael (25, 26). The predators Aulonium rufi-
corne (Olivier) (Coleoptera: Colytiidae) and
Laemophloeus spp. (Coleoptera: Cucujidae)
were found on material infested by P. bi-
color and another Phloeosinus species in Is-
rael (25). The parasitic mite Pyemotes tritici
Lagrèze-Fossat and Montane (Acarina: Pye-
motidae) achieved 67.3% parasitism 30 days
after its release under natural conditions in
China (35). The complex of the hymenopter-
an parasitoids consists of 6 pteromalids, 2
braconids, 1 eurytomid, 1 eulophid, 1 eu-
pelmid and 1 bethylid: Theocolax phloeosi-
ni sp.nov. (Hym.: Pteromalidae) on Juniperus
chinensis in China (34); Metacolus unifascia-
tus Forster (Hym.: Pteromalidae), Cerocepha-
la eccoptogastri Masi (Hym.: Pteromalidae),
Rhaphitelus maculatus Walker (Hym.: Pter-
omalidae), Heydenia pretiosa Forster (Hym.:
Pteromalidae), all on Mediterranean Cypress
in Israel (25, 26); Hecabolus sulcatus Curtis
(Hym.: Braconidae), Dendrosoter protuberans
(Nees) (Hym.: Braconidae) and the faculta-
tively parasitoid Eurytoma morio Boheman