172
N. WALOFF
Thus therc is an intricate network of relationships between L. orthotyli and L. ap*caZaa and their complexes of hosts. The numerical interactions of L. heterocordyli and Heterocurdylwr are simpler and are not
affected by the abundance of the later hatching species of broom
Miridae. This parrtsite and its host appear to exercise a regulating effect
on one another. So apparently do the earlier emerging strains of
L. orthotyli and Ascioderna, although this relationship is complicated
by the abundance of the alternate, host, 0. wirescens. In contrast, it
seems dbubtful that nymphal parasitism plays a major part in the
regulation of the three species of Qrthotylus (eee Table XLV) on broom.
It appears, however, that a degree of ecological homeostasis has evolved
between 0. adcmxurpi and 0. virescens and their nymphal parasites.
D. ARTHROPOD PREDATORS OF MIRIDAE ON BROOM
The arthropod predators of the five species of Miridae were studied
by the precipitin test (Dempster, 1966). Some twenty species of predator
were identified in which Heteroptera and various species of spiders
were numerically the most important. Over 6400 smears identified
the species which had fed on the minds and by far the largest number
of positives were obtained from various species of spiders (see Table
XLVIII). The three web-spinners, Meta, Araneua and Linyphia take
only adult bugs, the others take nymphs and adults as well. The
total number of spiders did not vary much during the three years of
thie study (1960-62), averaging about 10 per plant each year. The
numbers of individual species varied considerably however. The estimated rate of predation by spiders on Ortlrotylus adulta is given in
Table XLIX.
The feeding habits of three species of anthocorids have been analysed
by Dempster (1963). Anthucoris nenwrdis and A . sardhumni feed predominantly on broom psyllids, whereas A. newurn ie a more generd
predator. The broom miride are themselves predacious (see p. 173) and
are by far the most numerous predators living on broom and although
they do not feed at a very high rate (see TabIe XLVIII) they must take
considerable numbers of those species hatching later in the eeason.
Dempster (1960, 1964) considers that they mainly attack nymphs in
their first two instars. As Dempster (1960) points out mortality by
arthropod predators is likely to be highest during early nymphal life
and this will be particularly so for 0. vireacens and 0. concoEo7 which
hatch late in the season and are fed on by the earlier species of mirids.
Those predators which are capable of taking older nymphs, such as the
hunting spiders and nabids are present in lower numbers and predation
on older nymphs will be lees severe.
N. WALOFF
Thus therc is an intricate network of relationships between L. orthotyli and L. ap*caZaa and their complexes of hosts. The numerical interactions of L. heterocordyli and Heterocurdylwr are simpler and are not
affected by the abundance of the later hatching species of broom
Miridae. This parrtsite and its host appear to exercise a regulating effect
on one another. So apparently do the earlier emerging strains of
L. orthotyli and Ascioderna, although this relationship is complicated
by the abundance of the alternate, host, 0. wirescens. In contrast, it
seems dbubtful that nymphal parasitism plays a major part in the
regulation of the three species of Qrthotylus (eee Table XLV) on broom.
It appears, however, that a degree of ecological homeostasis has evolved
between 0. adcmxurpi and 0. virescens and their nymphal parasites.
D. ARTHROPOD PREDATORS OF MIRIDAE ON BROOM
The arthropod predators of the five species of Miridae were studied
by the precipitin test (Dempster, 1966). Some twenty species of predator
were identified in which Heteroptera and various species of spiders
were numerically the most important. Over 6400 smears identified
the species which had fed on the minds and by far the largest number
of positives were obtained from various species of spiders (see Table
XLVIII). The three web-spinners, Meta, Araneua and Linyphia take
only adult bugs, the others take nymphs and adults as well. The
total number of spiders did not vary much during the three years of
thie study (1960-62), averaging about 10 per plant each year. The
numbers of individual species varied considerably however. The estimated rate of predation by spiders on Ortlrotylus adulta is given in
Table XLIX.
The feeding habits of three species of anthocorids have been analysed
by Dempster (1963). Anthucoris nenwrdis and A . sardhumni feed predominantly on broom psyllids, whereas A. newurn ie a more generd
predator. The broom miride are themselves predacious (see p. 173) and
are by far the most numerous predators living on broom and although
they do not feed at a very high rate (see TabIe XLVIII) they must take
considerable numbers of those species hatching later in the eeason.
Dempster (1960, 1964) considers that they mainly attack nymphs in
their first two instars. As Dempster (1960) points out mortality by
arthropod predators is likely to be highest during early nymphal life
and this will be particularly so for 0. vireacens and 0. concoEo7 which
hatch late in the season and are fed on by the earlier species of mirids.
Those predators which are capable of taking older nymphs, such as the
hunting spiders and nabids are present in lower numbers and predation
on older nymphs will be lees severe.