STUDIES ON THE INSECT F A U N A ON SCOTCH BROOM
161
riws steadily as the brood grows older and takes up more space and
Fig. 8 illustrates the increase in competition with the rise in density.
Moreover, this intraspecific competition also had an indirect effect, aa
in very dense cultures many of the adufts that reached mat,urity were
small, failed to emerge from the galleries and died within them.
Yet another factor that caused death of H y h t i n u s was contributed
by the host plant. In contrast to Phloeophthutw which attacks dead
broom, Hylastinus attacks living plants. It is probable that the amount
of sap in the stem controls the initial choice of a site for gallery construction. On several occasions, however, sap-filled galleries with dead
eggs of H y h t i n u s were found on young healthy stems.
VII. SPECIES ON BROOM THAT ARE BOTH PRYTOPHAGOUS AND
PREDACIOUS; MIRIDAE, HETEROPTERA
It isxommonly supposed that closely related species of similar habits
are unlikely to occur in the same habitat, or if they do, their habits are
likely to change in some way. Therefore the occurrence of three closely
related species of Orthotylue, namely 0. adenoearpi (Perris), 0. virescens
(Douglas and Scott) and 0. concolor (Kirschbaum), of another Orthotyline - Heterocordylus tibialis (Hahn) and yet another Phyline mirid
of the same appearance and size, Asciodemu obsoletum (Fieber) on the
same host plant is a phenomenon of both ecological and evolutionary
interest. The first four species are essentially restricted to broom, while
the last is also found on gorse (Ulex europaewr L.).
From 1958 to 1965 0. W. Richards, J. P. Dempster and N. Waloff
have been studying the biology of these mirids and the following is an
account of some aspects of our work.
A. THE LIFE HISTORIES
The five species are univoltine, hatching from overwintered eggs in
early spring or early summer. Hetermdylus hatches first in March or
April, followed by Asciodema and 0. ademcarpi in April or May. 0.
virescens hatches from mid-May to early June and 0. concolor usually after
mid-June. Eclosion spreads over three months and this is reflected in
their geographical distribution. Thus, 0. adenocarpi has a wide southern
Atlantic range (Southwood, 1957), whereas 0. viresceas extends into
southern Europe, Asia Minor and North Africa (Stichel, 1937). The
distribution of 0. eoncolor is less well documented, but Southwood
(verbal communication) considers that it is probably not unlike that of
0. virescens and, if anything, it is relatively more abundant in southern
Europe.
Although there are days, or weeks, when the five species occur in the
161
riws steadily as the brood grows older and takes up more space and
Fig. 8 illustrates the increase in competition with the rise in density.
Moreover, this intraspecific competition also had an indirect effect, aa
in very dense cultures many of the adufts that reached mat,urity were
small, failed to emerge from the galleries and died within them.
Yet another factor that caused death of H y h t i n u s was contributed
by the host plant. In contrast to Phloeophthutw which attacks dead
broom, Hylastinus attacks living plants. It is probable that the amount
of sap in the stem controls the initial choice of a site for gallery construction. On several occasions, however, sap-filled galleries with dead
eggs of H y h t i n u s were found on young healthy stems.
VII. SPECIES ON BROOM THAT ARE BOTH PRYTOPHAGOUS AND
PREDACIOUS; MIRIDAE, HETEROPTERA
It isxommonly supposed that closely related species of similar habits
are unlikely to occur in the same habitat, or if they do, their habits are
likely to change in some way. Therefore the occurrence of three closely
related species of Orthotylue, namely 0. adenoearpi (Perris), 0. virescens
(Douglas and Scott) and 0. concolor (Kirschbaum), of another Orthotyline - Heterocordylus tibialis (Hahn) and yet another Phyline mirid
of the same appearance and size, Asciodemu obsoletum (Fieber) on the
same host plant is a phenomenon of both ecological and evolutionary
interest. The first four species are essentially restricted to broom, while
the last is also found on gorse (Ulex europaewr L.).
From 1958 to 1965 0. W. Richards, J. P. Dempster and N. Waloff
have been studying the biology of these mirids and the following is an
account of some aspects of our work.
A. THE LIFE HISTORIES
The five species are univoltine, hatching from overwintered eggs in
early spring or early summer. Hetermdylus hatches first in March or
April, followed by Asciodema and 0. ademcarpi in April or May. 0.
virescens hatches from mid-May to early June and 0. concolor usually after
mid-June. Eclosion spreads over three months and this is reflected in
their geographical distribution. Thus, 0. adenocarpi has a wide southern
Atlantic range (Southwood, 1957), whereas 0. viresceas extends into
southern Europe, Asia Minor and North Africa (Stichel, 1937). The
distribution of 0. eoncolor is less well documented, but Southwood
(verbal communication) considers that it is probably not unlike that of
0. virescens and, if anything, it is relatively more abundant in southern
Europe.
Although there are days, or weeks, when the five species occur in the