178
N. WALOFF
VIII. PREDATORS OF BROOM INSEOTS
A. THE PRRCLPITIN TEST
The fauna on broom is heavily preyed on by a large complex of
arthropod predators, both on the bushes and in broom litter. Birds also
feed on the insects exposed on the bushes in spring and summer and on
the stem miners in autumn and winter. A list of the most common predators is given in Table L I I , where predators which have been ascertained by the precipitin test are denoted by P, observed feeding in the
field by 0, and in the laboratory by L. This list of predators and of prey
is by no means exhaustive and probably the only insects that escape
the full onslaught of arthropod predation are those in protected microhabitats, i.e. within the broom pod and the stem mines. But even these
microhabitats do not afford full protection, aa the larvae of the midge
Lestodiplosis, within the pods, devour all the other living inhabitanta,
while the mines of the scoIytid beetles harbour the predacious Limop&ua ater.
In his work on predation on the broom fauna, Dempster carried out
over 40 000 precipitin tests. These were further supplemented by 2000
tests by Watmough (1963) and 1600 by Danthanmayana (1966).
Dempster’s papers on this subject (1959, 1960, 1963, 1964, 1966) form
a unique series, as he not only identified a large number of predators,
but also raised the subject to a quantitative level. To m e s s the effects
of predthors quantitatively, abundance of a prey and of i B potential
predators has to be known and also how long a meal will remain detectable within a predator’s gut. The details of the precipitin teat are
given in Dempster’s papers, but briefly it is b d on the interaction of
prey material in the gut of a predator with antibodies in the blood
serum of rabbits which have been inoculated with an extract of prey.
By these means Dempster (loc. cit.) identified the most important predators on broom and in the broom litter, the natural prey of three
species of Anthocoris on broom, the feeding habita of the five speciea of
broom Miridae and the arthropod predators of these Miridae.
It is always surprising to see the low percentage of any predator
population that is feeding on a prey (e.g. in Table LV) but there are
many predatory species, very few of them are selective in their diet
and their combined action may destroy an enormous proportion of a
prey population. Thus the arthropod predators accounted for 81% of
Phytodecta population recruited into Area 1 in 1958.
The most common prey on broom are psyllids, followed by aphids
and then by the moth Leucoptera. The five species of broom E d a a
rank very high in abundance, but they are phytophagous as well aa
predacious. Also, they both prey on other inaecta (including one another)
N. WALOFF
VIII. PREDATORS OF BROOM INSEOTS
A. THE PRRCLPITIN TEST
The fauna on broom is heavily preyed on by a large complex of
arthropod predators, both on the bushes and in broom litter. Birds also
feed on the insects exposed on the bushes in spring and summer and on
the stem miners in autumn and winter. A list of the most common predators is given in Table L I I , where predators which have been ascertained by the precipitin test are denoted by P, observed feeding in the
field by 0, and in the laboratory by L. This list of predators and of prey
is by no means exhaustive and probably the only insects that escape
the full onslaught of arthropod predation are those in protected microhabitats, i.e. within the broom pod and the stem mines. But even these
microhabitats do not afford full protection, aa the larvae of the midge
Lestodiplosis, within the pods, devour all the other living inhabitanta,
while the mines of the scoIytid beetles harbour the predacious Limop&ua ater.
In his work on predation on the broom fauna, Dempster carried out
over 40 000 precipitin tests. These were further supplemented by 2000
tests by Watmough (1963) and 1600 by Danthanmayana (1966).
Dempster’s papers on this subject (1959, 1960, 1963, 1964, 1966) form
a unique series, as he not only identified a large number of predators,
but also raised the subject to a quantitative level. To m e s s the effects
of predthors quantitatively, abundance of a prey and of i B potential
predators has to be known and also how long a meal will remain detectable within a predator’s gut. The details of the precipitin teat are
given in Dempster’s papers, but briefly it is b d on the interaction of
prey material in the gut of a predator with antibodies in the blood
serum of rabbits which have been inoculated with an extract of prey.
By these means Dempster (loc. cit.) identified the most important predators on broom and in the broom litter, the natural prey of three
species of Anthocoris on broom, the feeding habita of the five speciea of
broom Miridae and the arthropod predators of these Miridae.
It is always surprising to see the low percentage of any predator
population that is feeding on a prey (e.g. in Table LV) but there are
many predatory species, very few of them are selective in their diet
and their combined action may destroy an enormous proportion of a
prey population. Thus the arthropod predators accounted for 81% of
Phytodecta population recruited into Area 1 in 1958.
The most common prey on broom are psyllids, followed by aphids
and then by the moth Leucoptera. The five species of broom E d a a
rank very high in abundance, but they are phytophagous as well aa
predacious. Also, they both prey on other inaecta (including one another)