140
N. WALOFF
population of A. e p r t i i increased until 1961, when a crash occurred. Thie
was probably caused by intraspecific competition among the nymphs
for swollen buds which provide both food and shelter and a h by
emigration of a large proportion of the adult population. It is probable
that in 1961 the nymphal population of A. 8prtii was near the maximum that the habitat could support.
A. genistae is bivoltine, and in the expanding habitat its numbers
reached their peak in 1969, when predator numbers were low. High
numbers of this psyllid were maintained for three successive generations and then they crashed, This crash was probably caused by emigration of adults, which appears to be density dependent and by the action
of predators on the second generation.
The populations of A. genistcre never reached the high densities of
A. spurt4 probably because the latter species is a t an advantage,
hatching earlier in spring and occupying many of the available open
buds, i.e. the sites of food and shelter sought by both species.
c. PhZGdO9W8 &WdU% (FABRICIUS) A N D ITS EQQ PARASITES
The biology of a number of shield bugs and of their egg parmitea,
and of Piezodorw lituratw, which lives on broom and on gorse, haa
been studied by Javahery (1967). Piez&ua is univoltine and hibernates in the adult stage, away from the breeding site. In May the adults
immigrate into the broom plantation and the immature stages are
found between June and August. Adults of the new generation appear
in August. The population of this pentatomoid in Area 4 haa always
been low, the highest recorded number of nymphs being 6600 and that
of the adults 2000. In August the newly emerged adults feed, remain
immature and fly off to aestivate on the nearby deciduous and coniferous treee. There they do not feed, and remain immature and by
October migrate to sheltered hibernation sites under grasses and in
grass tussocks.
Fecundity of P i e z o d m waa investigated both in the field and in the
laboratory. In field conditions at an average temperature of 13"C, 13
females laid an average of 149 eggs in ten batches each. The average
fecundity of twenty females at 20°C waa forty-five eggs, that of twenty
females at 28°C thirty-nine eggs. The rapid fall off in reproductive rate
at the higher temperatures indicated that this shield bug is well
adjusted to the conditions of a temperate climate.
The eggs of Piezodorzls are attacked by four scelionid parasites, two
of the genus Aeokw and two of genus Telenumus. The two A s o h
species are new, whereas the T e l e m u a ( T . truncatue Mayr, and
T. 8okolovi M a p ) are new to Britain (Javahery, in preparation). In
Yateley, Hants, 44% of the 320 eggs of Piezodorwr collected on gorse
N. WALOFF
population of A. e p r t i i increased until 1961, when a crash occurred. Thie
was probably caused by intraspecific competition among the nymphs
for swollen buds which provide both food and shelter and a h by
emigration of a large proportion of the adult population. It is probable
that in 1961 the nymphal population of A. 8prtii was near the maximum that the habitat could support.
A. genistae is bivoltine, and in the expanding habitat its numbers
reached their peak in 1969, when predator numbers were low. High
numbers of this psyllid were maintained for three successive generations and then they crashed, This crash was probably caused by emigration of adults, which appears to be density dependent and by the action
of predators on the second generation.
The populations of A. genistcre never reached the high densities of
A. spurt4 probably because the latter species is a t an advantage,
hatching earlier in spring and occupying many of the available open
buds, i.e. the sites of food and shelter sought by both species.
c. PhZGdO9W8 &WdU% (FABRICIUS) A N D ITS EQQ PARASITES
The biology of a number of shield bugs and of their egg parmitea,
and of Piezodorw lituratw, which lives on broom and on gorse, haa
been studied by Javahery (1967). Piez&ua is univoltine and hibernates in the adult stage, away from the breeding site. In May the adults
immigrate into the broom plantation and the immature stages are
found between June and August. Adults of the new generation appear
in August. The population of this pentatomoid in Area 4 haa always
been low, the highest recorded number of nymphs being 6600 and that
of the adults 2000. In August the newly emerged adults feed, remain
immature and fly off to aestivate on the nearby deciduous and coniferous treee. There they do not feed, and remain immature and by
October migrate to sheltered hibernation sites under grasses and in
grass tussocks.
Fecundity of P i e z o d m waa investigated both in the field and in the
laboratory. In field conditions at an average temperature of 13"C, 13
females laid an average of 149 eggs in ten batches each. The average
fecundity of twenty females at 20°C waa forty-five eggs, that of twenty
females at 28°C thirty-nine eggs. The rapid fall off in reproductive rate
at the higher temperatures indicated that this shield bug is well
adjusted to the conditions of a temperate climate.
The eggs of Piezodorzls are attacked by four scelionid parasites, two
of the genus Aeokw and two of genus Telenumus. The two A s o h
species are new, whereas the T e l e m u a ( T . truncatue Mayr, and
T. 8okolovi M a p ) are new to Britain (Javahery, in preparation). In
Yateley, Hants, 44% of the 320 eggs of Piezodorwr collected on gorse