176
N. W U F F
mirida are declining, but they are all in the adult stage and take larger
meals. Moreover, by then broom begins to acquire a bedraggled appearance, the leaves turn yellow and bear numerous blotches inflicted by
0. vireeeene and by the other members of the large broom fauna. These
may be among the reasons why 0. concolor is the leaat abundant of the
species and its populations remain relatively small. For this reason it
was of great interest to eee the enormous populations of 0. concolor
in California, where it has been introduced together with the host plant
(Waloff, 1966).
Sarothamnua a q a r i u s has been introduced to north America partly
deliberately and partly inadvertently in ballaat (Lindroth, 1957). In the
Pacific northwest it has spread so much that it hrts to be controlled
(Holloway, 1964a). 0. concolor and 0. virescena have become established
on broom along the coastal belt in Northern California, but only
0. concolor has coloniaed the broom areaa on the Sierran foothills. In
British Columbia broom abounds along the southern coctet and forms
dense thickets on Vancouver Island. There, Asciodema is also found
aa well aa 0. wirescene and 0. concolor.
The enormous populations of 0. concoh in the Sierran foothills and
even larger ones of 0. virescena on Vancouver Island remind one of the
“ecological explosions” described by Elton (1958). These “explosions”,
however, are local and are primarily determined by the distribution and
abundance of the host plant. The abundance of 0. mdbr in California
and of 0. vire.9cen.s in British Columbia (see Table LI) may have
occurred partly in response to climatic conditions, but the pressure
imposed on these species by their natural enemies waa also relaxed.
The mirida appear to be only lightly paraaitised and the predatory and
numerow Heterocotdylols and 0. adenocarpi are absent (Waloff, loc. cit.).
Moreover, at leaat in California, the “clean” healthy condition of the
host plant itself also may have contributed to the expansion of 0. wnmlor populations, where it reaches abundenoe which exc8BczB that of all
the five species of broom mirida in southern England.
The sizes of the populations of 0. C012COIOT and of 0. Virescene in the
Pacific Northwest are at least suggestive of the degree of interactions
between the five species of Miridae on broom and 0. condor, which is
the last in the “pecking order” in southern England, may expand and
form enormous populetiom in the ebsenoe of the other epecies.
N. W U F F
mirida are declining, but they are all in the adult stage and take larger
meals. Moreover, by then broom begins to acquire a bedraggled appearance, the leaves turn yellow and bear numerous blotches inflicted by
0. vireeeene and by the other members of the large broom fauna. These
may be among the reasons why 0. concolor is the leaat abundant of the
species and its populations remain relatively small. For this reason it
was of great interest to eee the enormous populations of 0. concolor
in California, where it has been introduced together with the host plant
(Waloff, 1966).
Sarothamnua a q a r i u s has been introduced to north America partly
deliberately and partly inadvertently in ballaat (Lindroth, 1957). In the
Pacific northwest it has spread so much that it hrts to be controlled
(Holloway, 1964a). 0. concolor and 0. virescena have become established
on broom along the coastal belt in Northern California, but only
0. concolor has coloniaed the broom areaa on the Sierran foothills. In
British Columbia broom abounds along the southern coctet and forms
dense thickets on Vancouver Island. There, Asciodema is also found
aa well aa 0. wirescene and 0. concolor.
The enormous populations of 0. concoh in the Sierran foothills and
even larger ones of 0. virescena on Vancouver Island remind one of the
“ecological explosions” described by Elton (1958). These “explosions”,
however, are local and are primarily determined by the distribution and
abundance of the host plant. The abundance of 0. mdbr in California
and of 0. vire.9cen.s in British Columbia (see Table LI) may have
occurred partly in response to climatic conditions, but the pressure
imposed on these species by their natural enemies waa also relaxed.
The mirida appear to be only lightly paraaitised and the predatory and
numerow Heterocotdylols and 0. adenocarpi are absent (Waloff, loc. cit.).
Moreover, at leaat in California, the “clean” healthy condition of the
host plant itself also may have contributed to the expansion of 0. wnmlor populations, where it reaches abundenoe which exc8BczB that of all
the five species of broom mirida in southern England.
The sizes of the populations of 0. C012COIOT and of 0. Virescene in the
Pacific Northwest are at least suggestive of the degree of interactions
between the five species of Miridae on broom and 0. condor, which is
the last in the “pecking order” in southern England, may expand and
form enormous populetiom in the ebsenoe of the other epecies.