162
N. WALOFF
field simultaneously, the annual periods of their maximum abundanoe
are spread out in time.
The coexistence of the species is probably also facilitated by the
differences in the details of their behaviour. Although the hibernating
eggs are laid on broom twigs, different parts of the shoots are selected by
each of the species (Waloff and Southwood, 1960). Heterocordylw lays
most of its eggs in the wood of the two-year-old stems, 0. vireclceru on
the sides of the green, current year’s twigs, Asin the superficid
tissues of the leaf bases of green shoots, 0. cadenmu+ in 1- or 2-year-old
stems, its eggs lying outside the xylem cylinder usually with the opercula lodged in one of the five stem ridges. Most of the eggs of 0. concozot
are found in the lateral depressions below the ridges of young stems.
There are also some differences in the feeding habits of the five species
(Dempskr, 1960, 1964, 1966). The mode of feeding on the host plant
was determined by electrocuting individuals while they were feeding,
cutting off their styleta and sectioning the plant. With the exception of
0. virescem the minds fed by pushing their stylets into the phloem of
vascular bundles of young growing stems, or occasion@lly into the vein
of a leaf. Orthotylus virescen.3 haa a much shorter rostrum than the others
(Waloff and Southwood, loc. cit.) and extracts the contents only of the
palisade tissue or of spongy parenchyma of the leaves. Asciodemu feeds
on gorse aa well as on broom. By precipitin testa Dempster (1964)
showed that each species fed on broom to the same extent throughout
its life, i.e. from the first instar to the adult stage.
All the species are also predacious, but none showed specificity in
their attack (Dempster, 1964) and the species of prey taken depended
on its size and availability. In precipitin tests sera containing antibodies against psyllids, aphids and Brthdylus were used, but it proved
impossible to separate the different species of Orthotylw.
The rate of feeding of one species of mirid upon another was first
tested in laboratory experiments (Dempster, 1966), and these together
with the precipitin tests indicated that 0. virmm is less predacious
than the other mirids (Table XLI). Hetermdylw and Asciodemu were
also tested against anti-Orthotylus serum and the results confirmed that
both species were feeding on Orthot&us in the field. The rate at which
they were feeding waa greater than indicated by Table XLII, since the
first instar Orthotylus remained in the predator’s gut for only 4-7 h.
As 0. virescens and 0. concolor ere the latest to hatch, they are particularly prone to attack by the earlier end hence larger nymphs and
by the adults of the other broom Miridae.
However, by much the most common prey in the field are psyllids
and aphids. Psyllids are exceptionally numerous in early spring when
H e t e r m d y l u s is abundant and many of them are destroyed by this
N. WALOFF
field simultaneously, the annual periods of their maximum abundanoe
are spread out in time.
The coexistence of the species is probably also facilitated by the
differences in the details of their behaviour. Although the hibernating
eggs are laid on broom twigs, different parts of the shoots are selected by
each of the species (Waloff and Southwood, 1960). Heterocordylw lays
most of its eggs in the wood of the two-year-old stems, 0. vireclceru on
the sides of the green, current year’s twigs, Asin the superficid
tissues of the leaf bases of green shoots, 0. cadenmu+ in 1- or 2-year-old
stems, its eggs lying outside the xylem cylinder usually with the opercula lodged in one of the five stem ridges. Most of the eggs of 0. concozot
are found in the lateral depressions below the ridges of young stems.
There are also some differences in the feeding habits of the five species
(Dempskr, 1960, 1964, 1966). The mode of feeding on the host plant
was determined by electrocuting individuals while they were feeding,
cutting off their styleta and sectioning the plant. With the exception of
0. virescem the minds fed by pushing their stylets into the phloem of
vascular bundles of young growing stems, or occasion@lly into the vein
of a leaf. Orthotylus virescen.3 haa a much shorter rostrum than the others
(Waloff and Southwood, loc. cit.) and extracts the contents only of the
palisade tissue or of spongy parenchyma of the leaves. Asciodemu feeds
on gorse aa well as on broom. By precipitin testa Dempster (1964)
showed that each species fed on broom to the same extent throughout
its life, i.e. from the first instar to the adult stage.
All the species are also predacious, but none showed specificity in
their attack (Dempster, 1964) and the species of prey taken depended
on its size and availability. In precipitin tests sera containing antibodies against psyllids, aphids and Brthdylus were used, but it proved
impossible to separate the different species of Orthotylw.
The rate of feeding of one species of mirid upon another was first
tested in laboratory experiments (Dempster, 1966), and these together
with the precipitin tests indicated that 0. virmm is less predacious
than the other mirids (Table XLI). Hetermdylw and Asciodemu were
also tested against anti-Orthotylus serum and the results confirmed that
both species were feeding on Orthot&us in the field. The rate at which
they were feeding waa greater than indicated by Table XLII, since the
first instar Orthotylus remained in the predator’s gut for only 4-7 h.
As 0. virescens and 0. concolor ere the latest to hatch, they are particularly prone to attack by the earlier end hence larger nymphs and
by the adults of the other broom Miridae.
However, by much the most common prey in the field are psyllids
and aphids. Psyllids are exceptionally numerous in early spring when
H e t e r m d y l u s is abundant and many of them are destroyed by this