STUDIES O N THE INSECT FAUNA ON SCOTCH BROOM
153
c. THE BIOLOUY O F TWO SPECIES O F SCOLYTID BEETLES O N BROOM
AND THEIR HYMENOPTEROUS PABASITES (M. R. Smith, 1958)
Two bark beetles occur on broom at Silwood Park, Phloeophfhe
rliododactylw (Marsh.) and Hylaetinue obeeurw (Marsh.). The former
was more abundant in 1956-58 and was studied in greater detail.
Phbeop&horu.s always attacks dead or dying wood, whereas Hylautinus forms galleries in living wood. The two speciea therefore do not
compete with each other for food or space.
1. The gaUeries fomzed by the ecolytids
Phloeophthorms constructs the parent gallery immediately below the
cork of dead or dying wood. It is typically Y-shaped, the base of the Y
being short and the total length of both arms rarely exceeding 3 cm.
There is only one entrance and there are no ventilating holes. Both
sexes participate in construction of the gallery, which they inhabit and
the eggs &re lrcid during the construction in niches and sealed off with
cement wood dust. The larvae tend to avoid each other and their
galleries radiate at right angles to the parent gallery.
H y b t i n u s never attacks dead wood, but frequently attacks the main
stem or branches of large diameter, usually at points of some previous
injury. When the main stem is attacked the bush usually dies, though
not necessarily in the same year. Most of the attacked bushes in Areas
1 and 2 were very old and probably on the verge of death. Occasionally
stems recovered from the attack of Hylaetinus, but they were weakened
and fiactured in strong winds. In this species the parent gallery tends
to be T-shaped, the arms lying at right angles to the grain of wood.
Usually the length of the arms is about 4 cm. The larval galleries lie at
right angles to the parent gallery, i.e. longitudinally to the stem and
rewh the length of 4 to 5 cm; the whole system is very untidy.
2. Life hi8tWie8
(a) Phloeophthhorms rhododaetylus is known to occur on broom and on
gorse, but at Silwood it hus never been found on Ulex. In southern
England Phloeophthurus is univoltine, but its life history is complicated.
The species overwinters as larvae and adults. The adults emerge out of
the galleries in spring (March and April) and construct new galleries;
the overwintered larvae continue their development and emerge in
summer, mainly in June and July. There are therefore two peaks of
emergence. The progeny in the galleries constructed in spring overwinter as adults, whereas the progeny produced in galleries constructed
in summer overwinter as larvae. No larvae pupate after September and
all the pupae become adults which do not oviposit until the followi;.:
spring, Therefore there are no eggs or pupao in the galleries in winter.
153
c. THE BIOLOUY O F TWO SPECIES O F SCOLYTID BEETLES O N BROOM
AND THEIR HYMENOPTEROUS PABASITES (M. R. Smith, 1958)
Two bark beetles occur on broom at Silwood Park, Phloeophfhe
rliododactylw (Marsh.) and Hylaetinue obeeurw (Marsh.). The former
was more abundant in 1956-58 and was studied in greater detail.
Phbeop&horu.s always attacks dead or dying wood, whereas Hylautinus forms galleries in living wood. The two speciea therefore do not
compete with each other for food or space.
1. The gaUeries fomzed by the ecolytids
Phloeophthorms constructs the parent gallery immediately below the
cork of dead or dying wood. It is typically Y-shaped, the base of the Y
being short and the total length of both arms rarely exceeding 3 cm.
There is only one entrance and there are no ventilating holes. Both
sexes participate in construction of the gallery, which they inhabit and
the eggs &re lrcid during the construction in niches and sealed off with
cement wood dust. The larvae tend to avoid each other and their
galleries radiate at right angles to the parent gallery.
H y b t i n u s never attacks dead wood, but frequently attacks the main
stem or branches of large diameter, usually at points of some previous
injury. When the main stem is attacked the bush usually dies, though
not necessarily in the same year. Most of the attacked bushes in Areas
1 and 2 were very old and probably on the verge of death. Occasionally
stems recovered from the attack of Hylaetinus, but they were weakened
and fiactured in strong winds. In this species the parent gallery tends
to be T-shaped, the arms lying at right angles to the grain of wood.
Usually the length of the arms is about 4 cm. The larval galleries lie at
right angles to the parent gallery, i.e. longitudinally to the stem and
rewh the length of 4 to 5 cm; the whole system is very untidy.
2. Life hi8tWie8
(a) Phloeophthhorms rhododaetylus is known to occur on broom and on
gorse, but at Silwood it hus never been found on Ulex. In southern
England Phloeophthurus is univoltine, but its life history is complicated.
The species overwinters as larvae and adults. The adults emerge out of
the galleries in spring (March and April) and construct new galleries;
the overwintered larvae continue their development and emerge in
summer, mainly in June and July. There are therefore two peaks of
emergence. The progeny in the galleries constructed in spring overwinter as adults, whereas the progeny produced in galleries constructed
in summer overwinter as larvae. No larvae pupate after September and
all the pupae become adults which do not oviposit until the followi;.:
spring, Therefore there are no eggs or pupao in the galleries in winter.