STUDIES ON THE INSECT FAUNA ON SCOTCH BROOM
113
(a) The effecta of pardtea
The adults were destroyed by a hymenopterous, braconid praaite
Perilitus dubiue (Weamael) and by a fungus Bcauueria baesiana (Bals.)
Vuill. The braconid destroyed 6 1 3 % of the spring and &!By0 of the
autumn beetles. Although P . dubuis ie univoltine its emergence is in
some way controlled by the host, i.e. the parasites from the spring
beetles emerge earlier than from the autumn ones (Richards, 1960;
Waloff, 1961). The fungus, Beauweria deefroys the beetles chiefly during
hibernation. From 0 to 26% of beetles were infected in different years,
but as the early stages of infection cannot be identified in dissections,
these percentages are underestimated. A few lsrvae of Phytodeeta were
also killed by Beauveria.
Parasitism of the larvae was low and only between 1 and 3% were
parasitised by the fly Meigenia rnutabilis (FallBn) (Tachinidae). Occasional larval parasites included the fly MacquartMc brevicornis (Macq.)
= [occduea Rond.] (Tachinidae) (Richards and Waloff, 1900) and the
hymenopterous parasites (Nepieeta sp. (Ichneumonidae) and Peditus
dubuie, i.e. the parasite of the adult stage. Lees than 10% of the eggs
were paraaitised by Hymenoptera, i.e. by Trichog7amma sp. (Trichogrammatidae) and by Tetrwtichwr sp. ( I h b p h i k )
(b) The eflect8 of predator8
An important aspect of this study was the quantitative evaluation
of predation by invertebrates on the population of the beetle. Predatory
insects were by far the greatest single cause of mortality of the eggs
and larvae of Phytodecta. Because of the long oviposition period (86112 days) the immature stages of the beetle remained open to predation
throughout the summer. In the first half of the oviposition period the
numbers of eggs in the field were much lower than the calculated num, bers, while the incidence of larval stages was extremely low. The population curves of the offspring generation tend to show bimodality, the
second peak of the immature stages occurring late in the season, when
the number of the ovipositing beetles was already declining. Since the
immature stages were not; prone to any obvious disease and were only
lightly parasitised, predators were implicated and their seasonal abundance investigated. Simultaneously the numbers of the most common
alternate prey were considered. The latter included the aphids Aphie
8arothmni Frannsen and Acyrth8iphon 8 p r t i i (Koch) and the psyllids
Arytaina genktae (Latreille) and Arytaina epadii Guerin-MenBville. In
the last two years of this study predation wm estimated by serological
means, i.e. by the precipitin test which depends on the interaction of
the Phytodecta material in the gut of the predator with the antibodies
in the blood serum of rabbits which had been inoculated with the
extract of the beetle (see Dempster, 1960). After conducting over
113
(a) The effecta of pardtea
The adults were destroyed by a hymenopterous, braconid praaite
Perilitus dubiue (Weamael) and by a fungus Bcauueria baesiana (Bals.)
Vuill. The braconid destroyed 6 1 3 % of the spring and &!By0 of the
autumn beetles. Although P . dubuis ie univoltine its emergence is in
some way controlled by the host, i.e. the parasites from the spring
beetles emerge earlier than from the autumn ones (Richards, 1960;
Waloff, 1961). The fungus, Beauweria deefroys the beetles chiefly during
hibernation. From 0 to 26% of beetles were infected in different years,
but as the early stages of infection cannot be identified in dissections,
these percentages are underestimated. A few lsrvae of Phytodeeta were
also killed by Beauveria.
Parasitism of the larvae was low and only between 1 and 3% were
parasitised by the fly Meigenia rnutabilis (FallBn) (Tachinidae). Occasional larval parasites included the fly MacquartMc brevicornis (Macq.)
= [occduea Rond.] (Tachinidae) (Richards and Waloff, 1900) and the
hymenopterous parasites (Nepieeta sp. (Ichneumonidae) and Peditus
dubuie, i.e. the parasite of the adult stage. Lees than 10% of the eggs
were paraaitised by Hymenoptera, i.e. by Trichog7amma sp. (Trichogrammatidae) and by Tetrwtichwr sp. ( I h b p h i k )
(b) The eflect8 of predator8
An important aspect of this study was the quantitative evaluation
of predation by invertebrates on the population of the beetle. Predatory
insects were by far the greatest single cause of mortality of the eggs
and larvae of Phytodecta. Because of the long oviposition period (86112 days) the immature stages of the beetle remained open to predation
throughout the summer. In the first half of the oviposition period the
numbers of eggs in the field were much lower than the calculated num, bers, while the incidence of larval stages was extremely low. The population curves of the offspring generation tend to show bimodality, the
second peak of the immature stages occurring late in the season, when
the number of the ovipositing beetles was already declining. Since the
immature stages were not; prone to any obvious disease and were only
lightly parasitised, predators were implicated and their seasonal abundance investigated. Simultaneously the numbers of the most common
alternate prey were considered. The latter included the aphids Aphie
8arothmni Frannsen and Acyrth8iphon 8 p r t i i (Koch) and the psyllids
Arytaina genktae (Latreille) and Arytaina epadii Guerin-MenBville. In
the last two years of this study predation wm estimated by serological
means, i.e. by the precipitin test which depends on the interaction of
the Phytodecta material in the gut of the predator with the antibodies
in the blood serum of rabbits which had been inoculated with the
extract of the beetle (see Dempster, 1960). After conducting over