128
N. W A M F F
No increase in the population owurred during the second period of
growth of broom, i.e. after pod formation.
B. D. Smith waa the first to investigate the effects of predators on
the populations on broom and although, later, more precise meaeurements of predation were developed by Dempster (1960, 1963, 1964,
1966), Smith’s results remain of interest. Experimentally he estimated
the numbers of aphids consumed by the commonest predators per unit
of time and estimated the numbera of predators on broom simultaneously
with those of Acyrthsiphon. The majority of insect predators killed up
to 10 aphids per day (Bee Table XXI). Therefore, when the aphids were
most numerous, the predators could not have been responsible for more
than a few hundred aphids per day, whereaa the population in samples
was increasing by more than 1000 per day.
However, the level at which A . spartii is controlled at the trough of
the population curve may well be dependent upon the kill by invertebrate predators and this could affect the height of the “peak” in the
subsequent year.
(d) The eflects of hymenopterous parasites. Acyrthosiphn w&s parasitised
by three genera of primary parasites, namely two species of Aphidius,
one of Ephedrus and one of Praon. The degree of hyperparasitism was
low and the species bred out included Asaphes (Chalcidoidea), Lygmerus
(Cerophrontidae) and Charips (Cynipoidea).
The percentage parasitism at the peak of the aphid numbers waa low
in all 3 years (0.5 in 1955, 0.3 and 0.7 in the two subsequent years).
The primary parasites as they emerged during the summer moved on
to aphids elsewhere.
The black aphid, Aphis sarothamni, was only rarely paraaitised,
although its colonies were often adjacent to those of A c y r t h s i p h . It
is possible that protection from the parasitic Hymenoptera was
afforded by ants ( h i u s niger L.) which attended only Aphis
sarothamni,
B. POPULATION STUDIES OF TWO SPECIES OF
PSYLLIDAE ON BROOM
Watmough (1963) etudied the two species of broom psyllids Arytaina
spartii Guerin-MenBville and -4rytaina genie2ae Latreille between 1960
and 1969 in Area 4. Apart from the extensive work of Clark (1962,
1963a, 1983b) in Australia, this is the only other study of populations
of PRyllidm.
1. L(fe histories
A . spartii is univoltine with a diapause in the egg stage. The eggs are
embedded in the surfaces of young shoots and their exposed sides are
N. W A M F F
No increase in the population owurred during the second period of
growth of broom, i.e. after pod formation.
B. D. Smith waa the first to investigate the effects of predators on
the populations on broom and although, later, more precise meaeurements of predation were developed by Dempster (1960, 1963, 1964,
1966), Smith’s results remain of interest. Experimentally he estimated
the numbers of aphids consumed by the commonest predators per unit
of time and estimated the numbera of predators on broom simultaneously
with those of Acyrthsiphon. The majority of insect predators killed up
to 10 aphids per day (Bee Table XXI). Therefore, when the aphids were
most numerous, the predators could not have been responsible for more
than a few hundred aphids per day, whereaa the population in samples
was increasing by more than 1000 per day.
However, the level at which A . spartii is controlled at the trough of
the population curve may well be dependent upon the kill by invertebrate predators and this could affect the height of the “peak” in the
subsequent year.
(d) The eflects of hymenopterous parasites. Acyrthosiphn w&s parasitised
by three genera of primary parasites, namely two species of Aphidius,
one of Ephedrus and one of Praon. The degree of hyperparasitism was
low and the species bred out included Asaphes (Chalcidoidea), Lygmerus
(Cerophrontidae) and Charips (Cynipoidea).
The percentage parasitism at the peak of the aphid numbers waa low
in all 3 years (0.5 in 1955, 0.3 and 0.7 in the two subsequent years).
The primary parasites as they emerged during the summer moved on
to aphids elsewhere.
The black aphid, Aphis sarothamni, was only rarely paraaitised,
although its colonies were often adjacent to those of A c y r t h s i p h . It
is possible that protection from the parasitic Hymenoptera was
afforded by ants ( h i u s niger L.) which attended only Aphis
sarothamni,
B. POPULATION STUDIES OF TWO SPECIES OF
PSYLLIDAE ON BROOM
Watmough (1963) etudied the two species of broom psyllids Arytaina
spartii Guerin-MenBville and -4rytaina genie2ae Latreille between 1960
and 1969 in Area 4. Apart from the extensive work of Clark (1962,
1963a, 1983b) in Australia, this is the only other study of populations
of PRyllidm.
1. L(fe histories
A . spartii is univoltine with a diapause in the egg stage. The eggs are
embedded in the surfaces of young shoots and their exposed sides are