STUDIES ON THE INSECT FAUNA ON SCOTCH BROOM
176
biological competition is greatest between congeneric species is incorrect, or there is some more dominating influence in the opposite
direction which overshadows any effect of competition.
Although the five species of Miridae have similar life histories and
co-exist on the same host plant, and although the three species of
Orthotylw are closely related, it is doubtful whether they can be wferred to aa true ecological homologuee (Waloff, 1966). Their dates of
eclosion from the overwintered eggs and henw the annual peaks in
populations are spaced out in time. It is true that Asciodema and
0. adenocarpi overlap closely, but the latter species is confined to broom
whereas AsciaEema haa an alternate host plant in gorse. There are also
differences in behaviour. For instanoe in the choice of oviposition sites
by each species, in the rates of dispersal of the adults from the breeding
sites (p. 190) and in the feeding habits in at least two of the species.
0. virescens has a much shorter rostrum than the others and is considerably less predacious, whereas AsciodenuG can feed on gorse as well
aa on broom.
Heterocordylus is the first to hatch in spring. Its population is more
isolated in time and appears to interact closely with that of its nymphal
parasite Leiophron hterocordyli. This mirid also escapes the two other
Leiophron species which attack the other broom bugs. But there is a
cries-crow network of relations between L. orthotyli and its two main
hosts, Asciodema and 0. virescens and a h between L. apicalis and
0. adenocarpi and 0. concolor. The populations of these parasites expand
and contract within those of their alternate hosts. When one host become8 more abundant than the other, the braconid population may
expand within it and in time will exercise severe pressure on the population of the less abundant host. This appeared to happen when the
population of 0. virescene expanded in 1902 and that of Asciodema was
heavily parasitised for two consecutive years. In this way the mirid
populations affect one mother indirectly. The direct effect is through
predation.
All broom Miridae are predacious as well aa phytophagous, moreover
they outnumber all the other predators on broom. Dempster has repeatedly shown that they indulge in fratricidal predation and there is
little reason to think that they are not cannibalistic. As Dempster (1966)
considers that they mainly feed on the first, two nymphal instars, the
numbers of the early hatching Heterocordylw are not affected by the
abundance ofi'the other four species. The late hatching 0. virmcens
appears to be severely attacked by the predacious Heterocordylus,
Asciodema and the most abundant of the five species - 0. adenocarpi.
CbtbtyZm virescens itself is mainly phytophagous and takes little animal
food. By the time 0. concolor hatches the populations of the first three
176
biological competition is greatest between congeneric species is incorrect, or there is some more dominating influence in the opposite
direction which overshadows any effect of competition.
Although the five species of Miridae have similar life histories and
co-exist on the same host plant, and although the three species of
Orthotylw are closely related, it is doubtful whether they can be wferred to aa true ecological homologuee (Waloff, 1966). Their dates of
eclosion from the overwintered eggs and henw the annual peaks in
populations are spaced out in time. It is true that Asciodema and
0. adenocarpi overlap closely, but the latter species is confined to broom
whereas AsciaEema haa an alternate host plant in gorse. There are also
differences in behaviour. For instanoe in the choice of oviposition sites
by each species, in the rates of dispersal of the adults from the breeding
sites (p. 190) and in the feeding habits in at least two of the species.
0. virescens has a much shorter rostrum than the others and is considerably less predacious, whereas AsciodenuG can feed on gorse as well
aa on broom.
Heterocordylus is the first to hatch in spring. Its population is more
isolated in time and appears to interact closely with that of its nymphal
parasite Leiophron hterocordyli. This mirid also escapes the two other
Leiophron species which attack the other broom bugs. But there is a
cries-crow network of relations between L. orthotyli and its two main
hosts, Asciodema and 0. virescens and a h between L. apicalis and
0. adenocarpi and 0. concolor. The populations of these parasites expand
and contract within those of their alternate hosts. When one host become8 more abundant than the other, the braconid population may
expand within it and in time will exercise severe pressure on the population of the less abundant host. This appeared to happen when the
population of 0. virescene expanded in 1902 and that of Asciodema was
heavily parasitised for two consecutive years. In this way the mirid
populations affect one mother indirectly. The direct effect is through
predation.
All broom Miridae are predacious as well aa phytophagous, moreover
they outnumber all the other predators on broom. Dempster has repeatedly shown that they indulge in fratricidal predation and there is
little reason to think that they are not cannibalistic. As Dempster (1966)
considers that they mainly feed on the first, two nymphal instars, the
numbers of the early hatching Heterocordylw are not affected by the
abundance ofi'the other four species. The late hatching 0. virmcens
appears to be severely attacked by the predacious Heterocordylus,
Asciodema and the most abundant of the five species - 0. adenocarpi.
CbtbtyZm virescens itself is mainly phytophagous and takes little animal
food. By the time 0. concolor hatches the populations of the first three