DYNAMICS O F FIELD POPULATION OF PINE LOOPER
209
B. THE LIFECYCLE OF THE PINE LOOPER
The geometrid, Bupalus piniarius L., chosen as an object for this
study, is univoltine (Fig. 1). The moths emerge from the litter in MayJune over a period of nearly five weeks. This emergence has a daily
periodicity, the moths appearing between 7 and 9 hr. The males start
appearing some days earlier than the females.
Immediately after having reached the surface the adults search for
an object, e.g. a small protruding stick, which enables them to hang
upside down and freely expand the wings to their full size. One or two
hours later, depending on temperature, the insects take flight. The
females soon settle down in the tree crowns, whereas the males take
part in a tumbling courtship flight, exhibited around the crowns during
the morning hours, i.e. shortly after the emergence of the females. The
function of this flight can be interpreted as a search for virgin females.
Copulation usually take place in the crowns, and 10-20 hours later the
females start egg deposition.
The eggs are deposited on the needles in clusters of 2 to 25. After
each act of oviposition the moth has a period of rest, and- before
resuming the laying act again - a short flight is performed as a result
of which the nearly 180 eggs of one female are more or less randomly
distributed on the crowns of several trees. The total number of eggs of
one female is laid within 8-14 days, the lifetime being highly dependent
on temperature. Normally, the last females t o emerge die about mid
July. After its natural death the oviduct of the female may still contain
up to 10 mature eggs with fully developed chorion; in the ovarioles,
a large number of oocytes in all stages of development is always
present.
The first instar larvae hatch about 20 days after oviposition. They
bite a hole in the chorion and leave it, but do not eat it, so that the
empty egg shells are still present on the needles some weeks after
hatching .
The young larvae disperse by crawling and soon afterwards start to
eat, making small grooves in the needles. The growth of the larvae is
slow, passing through five or six instars from 1,he beginning of July up
to mid October. During this period there is ctn enormous increase in
size, the body length increasing from 3 mm immediately after hatching,
up to 40 mm when fully grown.
The larvae descend to the litter from the beginning of October up to
mid November. They simply fall from the twjgs on to the moss cover
and normally penetrate into the litter layer with@ 10-15 minutes,
during which period they crawl around, presumably in search of a suitable place for penetration. The larvae which are ready to descend are
209
B. THE LIFECYCLE OF THE PINE LOOPER
The geometrid, Bupalus piniarius L., chosen as an object for this
study, is univoltine (Fig. 1). The moths emerge from the litter in MayJune over a period of nearly five weeks. This emergence has a daily
periodicity, the moths appearing between 7 and 9 hr. The males start
appearing some days earlier than the females.
Immediately after having reached the surface the adults search for
an object, e.g. a small protruding stick, which enables them to hang
upside down and freely expand the wings to their full size. One or two
hours later, depending on temperature, the insects take flight. The
females soon settle down in the tree crowns, whereas the males take
part in a tumbling courtship flight, exhibited around the crowns during
the morning hours, i.e. shortly after the emergence of the females. The
function of this flight can be interpreted as a search for virgin females.
Copulation usually take place in the crowns, and 10-20 hours later the
females start egg deposition.
The eggs are deposited on the needles in clusters of 2 to 25. After
each act of oviposition the moth has a period of rest, and- before
resuming the laying act again - a short flight is performed as a result
of which the nearly 180 eggs of one female are more or less randomly
distributed on the crowns of several trees. The total number of eggs of
one female is laid within 8-14 days, the lifetime being highly dependent
on temperature. Normally, the last females t o emerge die about mid
July. After its natural death the oviduct of the female may still contain
up to 10 mature eggs with fully developed chorion; in the ovarioles,
a large number of oocytes in all stages of development is always
present.
The first instar larvae hatch about 20 days after oviposition. They
bite a hole in the chorion and leave it, but do not eat it, so that the
empty egg shells are still present on the needles some weeks after
hatching .
The young larvae disperse by crawling and soon afterwards start to
eat, making small grooves in the needles. The growth of the larvae is
slow, passing through five or six instars from 1,he beginning of July up
to mid October. During this period there is ctn enormous increase in
size, the body length increasing from 3 mm immediately after hatching,
up to 40 mm when fully grown.
The larvae descend to the litter from the beginning of October up to
mid November. They simply fall from the twjgs on to the moss cover
and normally penetrate into the litter layer with@ 10-15 minutes,
during which period they crawl around, presumably in search of a suitable place for penetration. The larvae which are ready to descend are