RTI’1,II:S O N THE INBF,(’T V A V N A O N SCOTCH BROOM
107
within the pod wvity and dwellere within the pod gall produced by the
nritlgi. A ~ p h . f m 4 l i n nurotharnni. Ettch cwmplex is charactcrid by ito
own aet of hymmoptcrous parasites. The pod dwellers have one feature
in common, they overwinter either as adults, pupae or last instar larvae.
The temporary nature of the habitat excludes all species that overwinter aa eggs or young larvae. It is also surmised that all the twentythree species are able to live in this temporary ecological niche because
their life histories are spread out in time and their requirements for
space and food are sufficiently diverse.
The microhabitat ibelf is affected by the age of the host plant, since
older bushes produce smaller pods with fewer seeds. Thus the larvae
of the seed feeders, Apion and Bruchidius have a slightly reduced
chance of finding a seed in each consecutive year on the same bush.
Whether there is an alteration in the ‘food value’ of the seeds and the
pod tissues remains unknown. Another feature of this temporary habitat is “pod dehiscence”. Many larvae of Apion and their hymenopterous parasites are ejected and presumably die if they are too small to
pupate. Bruchidius larvae and their parasites are more protected in the
“cement cells” and probably complete development after they are flung
out with the seeds. Many midge larvae of Clinodipbcris and Leatodiplosicr are also ejected and unless they are fully grown, presumably die.
Although climatic changes cannot regulate an insect population they
may bring about drastic changes. This was seen in 1961 when the hot
dry weather of early spring was followed by sharp frosts at the end of
May. The early warm weather caused Asphondylia adults to emerge
from the bud galls before the pods were formed, i.e. emergence of the
midge and availability of habitat failed to synchronise. The direct effect
of frosts in May was to kill many growing pods (62% in Area 4) and
hence the eggs of the seed beetles laid on and in them. The indirect
effect was in the drastic reduction of the oviposition sites and the
consequent overcrowding and intraspecific competition for seeds
amongst the larvae of Bruchidius. As only one larva can develop in a
seed there was, simultaneously, interspecific competition between
Bruchidius and Apion larvae, the latter species being a t an advantage,
since it hatches first and its larvae have the “fir& choice” of feeding
sites.
Znter~pecifici rompetition also occurred between the midge larvae
within the pod gall. The gall of Asphondylia is a plant growth which
develops in response to insect infection and the midge larva develops
in the habitat of its own formation. The galls often contain the inquiline
specics Trotteria, which develops at the expense of the primary species.
Asphondylia is often “irritated” by the active larvae of the invader
and prevented from feeding and pupating.
107
within the pod wvity and dwellere within the pod gall produced by the
nritlgi. A ~ p h . f m 4 l i n nurotharnni. Ettch cwmplex is charactcrid by ito
own aet of hymmoptcrous parasites. The pod dwellers have one feature
in common, they overwinter either as adults, pupae or last instar larvae.
The temporary nature of the habitat excludes all species that overwinter aa eggs or young larvae. It is also surmised that all the twentythree species are able to live in this temporary ecological niche because
their life histories are spread out in time and their requirements for
space and food are sufficiently diverse.
The microhabitat ibelf is affected by the age of the host plant, since
older bushes produce smaller pods with fewer seeds. Thus the larvae
of the seed feeders, Apion and Bruchidius have a slightly reduced
chance of finding a seed in each consecutive year on the same bush.
Whether there is an alteration in the ‘food value’ of the seeds and the
pod tissues remains unknown. Another feature of this temporary habitat is “pod dehiscence”. Many larvae of Apion and their hymenopterous parasites are ejected and presumably die if they are too small to
pupate. Bruchidius larvae and their parasites are more protected in the
“cement cells” and probably complete development after they are flung
out with the seeds. Many midge larvae of Clinodipbcris and Leatodiplosicr are also ejected and unless they are fully grown, presumably die.
Although climatic changes cannot regulate an insect population they
may bring about drastic changes. This was seen in 1961 when the hot
dry weather of early spring was followed by sharp frosts at the end of
May. The early warm weather caused Asphondylia adults to emerge
from the bud galls before the pods were formed, i.e. emergence of the
midge and availability of habitat failed to synchronise. The direct effect
of frosts in May was to kill many growing pods (62% in Area 4) and
hence the eggs of the seed beetles laid on and in them. The indirect
effect was in the drastic reduction of the oviposition sites and the
consequent overcrowding and intraspecific competition for seeds
amongst the larvae of Bruchidius. As only one larva can develop in a
seed there was, simultaneously, interspecific competition between
Bruchidius and Apion larvae, the latter species being a t an advantage,
since it hatches first and its larvae have the “fir& choice” of feeding
sites.
Znter~pecifici rompetition also occurred between the midge larvae
within the pod gall. The gall of Asphondylia is a plant growth which
develops in response to insect infection and the midge larva develops
in the habitat of its own formation. The galls often contain the inquiline
specics Trotteria, which develops at the expense of the primary species.
Asphondylia is often “irritated” by the active larvae of the invader
and prevented from feeding and pupating.