108
N. WALOFF
Other interactions between the species included the effects of parasites. Over 80% of the Apion larvae on old broom were killed by
ectoparasites in 1960; various species were involved but the main one
was Iiabrocytus sequestor. In the same year, in the new broom area,
40% of Bruchidius larvae were killed by parasites, mainly by Trimpis
and to a lesser extent by Ilabrocytus.
In the pod gall, Asphondyliu is strictly parasitised only by PseudoCatoEaccUs and Eupelmus, since Aprostocetus larvae feed on Asphndylia
larvae, the fungal mycelium and t'he pod tissues. Moreover, Aprostwetus kills an Asphondylia larva before it oviposits on it, and thus
may be regarded more as a predator than a parasite.
Hyperparasitism is quit.e common in all the three complexes of insects
within the pod. Exact timing is important in this precarious mode of
life, but failure to synchronise the life histories of hosts and hyperparasites was common and frequentfly Mesopohbus larvae died of starvation when they developed from eggs laid on larvae of Habrocytw
which were too small.
In contrast to parasitism and to interspecific competition, predation
is not an important factor in population regulation within the broom
pod, since all the three complexes of insects are separated from each
other and protected from many external invertebrate predators. The
exceptions to this are the eggs of Rruchidiw which are laid on the
outside walls of pods and are exposed to the numerous predacious
species 3n broom. The larvae of the midge Lestodipl08is within the pods
are also predacious and kill many larvae of the phytophagous Clinod i p h i s and any other insects they encounter.
I V . PHYTOPHAGOUS INSECTS; DEFOLIATORS
Amongst the most common species that feed on broom leaves and
young stems at Silwood Park are the larval and adult stages of the
chrysomelid Phytodectn olivacea (Forster), the adults of the curculionid
Sitona regensteinensis Hbst., and the larvae of two geometrid moths
Chesias rufata (Fabricius) and C . legatella (Schiffermueller). These species
were never observed to cause defoliation of the broom bushes at
Silwood, although in some years they were abundant.
A. THE S T U D Y O F T H E NATURAL POPULATION O F
PHYTODECTA OLIVACEA
This study was made in broom Area 1. Some records of the numbers
of adult beetles were obtained in 1948-59, but detailed estimates were
made only from 1954 to 1959 (Richards and Waloff, 1961).
N. WALOFF
Other interactions between the species included the effects of parasites. Over 80% of the Apion larvae on old broom were killed by
ectoparasites in 1960; various species were involved but the main one
was Iiabrocytus sequestor. In the same year, in the new broom area,
40% of Bruchidius larvae were killed by parasites, mainly by Trimpis
and to a lesser extent by Ilabrocytus.
In the pod gall, Asphondyliu is strictly parasitised only by PseudoCatoEaccUs and Eupelmus, since Aprostocetus larvae feed on Asphndylia
larvae, the fungal mycelium and t'he pod tissues. Moreover, Aprostwetus kills an Asphondylia larva before it oviposits on it, and thus
may be regarded more as a predator than a parasite.
Hyperparasitism is quit.e common in all the three complexes of insects
within the pod. Exact timing is important in this precarious mode of
life, but failure to synchronise the life histories of hosts and hyperparasites was common and frequentfly Mesopohbus larvae died of starvation when they developed from eggs laid on larvae of Habrocytw
which were too small.
In contrast to parasitism and to interspecific competition, predation
is not an important factor in population regulation within the broom
pod, since all the three complexes of insects are separated from each
other and protected from many external invertebrate predators. The
exceptions to this are the eggs of Rruchidiw which are laid on the
outside walls of pods and are exposed to the numerous predacious
species 3n broom. The larvae of the midge Lestodipl08is within the pods
are also predacious and kill many larvae of the phytophagous Clinod i p h i s and any other insects they encounter.
I V . PHYTOPHAGOUS INSECTS; DEFOLIATORS
Amongst the most common species that feed on broom leaves and
young stems at Silwood Park are the larval and adult stages of the
chrysomelid Phytodectn olivacea (Forster), the adults of the curculionid
Sitona regensteinensis Hbst., and the larvae of two geometrid moths
Chesias rufata (Fabricius) and C . legatella (Schiffermueller). These species
were never observed to cause defoliation of the broom bushes at
Silwood, although in some years they were abundant.
A. THE S T U D Y O F T H E NATURAL POPULATION O F
PHYTODECTA OLIVACEA
This study was made in broom Area 1. Some records of the numbers
of adult beetles were obtained in 1948-59, but detailed estimates were
made only from 1954 to 1959 (Richards and Waloff, 1961).