Biology Reference
In-Depth Information
Structure does not
consistently
transport fungi
Structure
consistently
transports fungi
PIT
(with
no to few setae)
SAC
(pocket/tube)
SETAL
BRUSH
Glandular
Nonglandular
Glandular
Nonglandular
Glandular
Nonglandular
Glandular
Pit
Mycangium
Nonglandular
Pit
Mycangium
Glandular
Sac
Mycangium
Nonglandular
Sac
Glandular
Brush
Mycangium
Nonglandular
Brush
Mycangium
Mycangium
FIGURE 7.2
Schematic for classiÝcation of mycangia by coarse structure and presence of glands.
have been observed, but their Ýne structure has not been fully described (Farris and Funk, 1965;
Livingston and Berryman, 1972). A number of glandular types are associated with insect exoskel-
etons (Noirot and Quennedey, 1974). Bark and ambrosia beetle mycangial glands thus far described
are most commonly class III glands (glands with direct ducts to the surface of the exoskeleton)
(Farris and Funk, 1965; Schneider and Rudinsky, 1969; Barras and Perry, 1971; Levieux et al.,
1991), although some mycangia may be associated with more than one gland type (Happ et al.,
1971; Cassier et al., 1996).
The secretions produced by glands associated with bark beetle mycangia are believed to support
the growth of fungal propagules, protect spores and mycelium from desiccation, and act selectively
against fungi not symbiotic with the beetle (Schneider and Rudinsky, 1969; Happ et al., 1971;
Barras and Perry, 1971; Barras and Perry, 1972; Paine and Birch, 1983). Glandular secretions of
several ambrosia beetles contain fatty acids, phospholipids, sterols, and amino acids and inÞuence
the growth of ambrosial fungi while in the mycangium (Norris, 1979). Glands associated with
mycangia of the related bark beetles may produce similar secretions and function in a similar
manner, but there have been few if any studies to document the nature and function of gland
products in these insects.
Mycangia have arisen independently several times in the Scolytidae, underscoring the impor-
tance of fungi to this group of beetles. Although type of mycangium is often genus speciÝc, the
presence or type of mycangium can vary even within a single genus. For example, within
Dendroctonus
, Ýve species possess complex glandular sac mycangia on the pronotum functional
only in females (Barras and Perry, 1971, 1972), while two species possess sac mycangia (glan-
dular status unknown) on the maxillary cardines that are functional in both sexes (Whitney and
Farris, 1970; Six and Paine, 1997). Still other
species possess pit mycangia
consisting of shallow pits in combination with sparse setae (Lewinsohn et al., 1994). Some
Dendroctonus
Dendroctonus
species, including
D. valens
LeConte,
D. micans
(Kugelann), and
D. terebrans
(Olivier), remain uninvestigated for the presence of mycangia; however, as these beetles show
little consistency in fungal associates (Lieutier et al., 1992; Klepzig et al., 1995; D.L. Six,
unpublished data), they may be nonmycangial.
F
A
UNGAL
DAPTATIONS
Ophiostomatoid fungi are well adapted to dispersal by arthropods (Malloch and Blackwell, 1993).
Most produce ascomata with ostiolate necks that extrude ascospores (sexual spores) at heights
where they are most likely to be encountered by insects and other arthropods. Ascospores are
