STUDIES OH THE INSECT FAUNA ON SCOTCH BBOOH
146
2. The 2ife h i d a y
L. spartijoliella is univoltine and overwinters in the larval stage in
green broom twigs. Adult emergence begins in the first half of June and
reaches its peak in early July. There is a rapid fall off in numbers and
only a few moths remain in the field by late Auguat. The life of the
adult population is long and is determined by its protracted emergence;
life of individual moths last only 14-2 weeks.
The females emerge with about one-third of their eggs mature, but
oviposit only after copulation which takes place within a week after
emergence. Most eggs are laid on the young twigs of the lower branches,
this habit reflecting the height of flight of the females. Fecundity and
longevity of the moths is directly correlated with temperature. Under
experimental conditions the greatest number of eggs was laid at 20°C
(a mean of 72, limits 56139) i.e. at the mean summer temperature of
a temperate climate.
After 13-18 days incubation the small yellow larvae eat their way
through the chorion directly into the plant tissues. There are six larval
instars and the first five are within the linear mine. Only one larva
occupies a mine. Overwintering is in the 3rd, 4th and 5th larval instars,
the three stages occurring simultaneously. The larvae are well adapted
to withstand low temperatures, the undercooling points of the fourth
and fifth instars being -17°C an4 of the sixth -13.7"C. Throughout
the winter, feeding and moulting are retarded, but not completely
stopped and by April all the larvae reach the sixth and their final
instar. They continue to feed within the mine for three to four weeks
and then assume a wandering stage, leaving the mine and pupating in
spindle-shaped cocoons on the sides of twigs. The length of the pupal
period is approximately six weeks.
3. The nzetlwds of eampling a d e e t i d b n of recruitment and d i t y
The immature stages were sampled by examination of broom cuttings
of known weight. The total amount of the gwen broom material in
Area 4 waa also estimated. The addlts were sampled by beating eighths
of broom bushes onto a collecting tray and by recording the numbers
emerging in muslin cages, which enclosed known fractions of the bushes.
Throughout the 3 years of this study there was always an excess of
emerging males and the sex ratio was 18:049? in 1904, 1&0.72? in
1905 and 13:0.989 in 1966. Moreover, more females than males flew
out of the plantation and dispersd. The methods of sampling moths
in flight are described in another section (p. 190).
The regrension equation method (Richards and Waloff, 1954) for
estimating the numbers recruited at each stage w m suitable for the
analysis of the sampling data, but fecundity in the field was calculated
146
2. The 2ife h i d a y
L. spartijoliella is univoltine and overwinters in the larval stage in
green broom twigs. Adult emergence begins in the first half of June and
reaches its peak in early July. There is a rapid fall off in numbers and
only a few moths remain in the field by late Auguat. The life of the
adult population is long and is determined by its protracted emergence;
life of individual moths last only 14-2 weeks.
The females emerge with about one-third of their eggs mature, but
oviposit only after copulation which takes place within a week after
emergence. Most eggs are laid on the young twigs of the lower branches,
this habit reflecting the height of flight of the females. Fecundity and
longevity of the moths is directly correlated with temperature. Under
experimental conditions the greatest number of eggs was laid at 20°C
(a mean of 72, limits 56139) i.e. at the mean summer temperature of
a temperate climate.
After 13-18 days incubation the small yellow larvae eat their way
through the chorion directly into the plant tissues. There are six larval
instars and the first five are within the linear mine. Only one larva
occupies a mine. Overwintering is in the 3rd, 4th and 5th larval instars,
the three stages occurring simultaneously. The larvae are well adapted
to withstand low temperatures, the undercooling points of the fourth
and fifth instars being -17°C an4 of the sixth -13.7"C. Throughout
the winter, feeding and moulting are retarded, but not completely
stopped and by April all the larvae reach the sixth and their final
instar. They continue to feed within the mine for three to four weeks
and then assume a wandering stage, leaving the mine and pupating in
spindle-shaped cocoons on the sides of twigs. The length of the pupal
period is approximately six weeks.
3. The nzetlwds of eampling a d e e t i d b n of recruitment and d i t y
The immature stages were sampled by examination of broom cuttings
of known weight. The total amount of the gwen broom material in
Area 4 waa also estimated. The addlts were sampled by beating eighths
of broom bushes onto a collecting tray and by recording the numbers
emerging in muslin cages, which enclosed known fractions of the bushes.
Throughout the 3 years of this study there was always an excess of
emerging males and the sex ratio was 18:049? in 1904, 1&0.72? in
1905 and 13:0.989 in 1966. Moreover, more females than males flew
out of the plantation and dispersd. The methods of sampling moths
in flight are described in another section (p. 190).
The regrension equation method (Richards and Waloff, 1954) for
estimating the numbers recruited at each stage w m suitable for the
analysis of the sampling data, but fecundity in the field was calculated