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Forest Semilooper
 
Insect:  Declana floccosa Walker (Lepidoptera: Geometridae)



Forest and Timber Insects in New Zealand No. 50
 
Based on M.K. Kay (1982)
 

Fig.1 - Adults of the forest semilooper are highly variable in wing colour and patterning.  Actual size.

Type of injury
The caterpillar of Declana floccosa eats the foliage of host plants.
 
Hosts
The caterpillar feeds on a wide range of native and exotic broad-leaved and coniferous shrubs
and trees. Exotic hosts include Pinus radiata (radiata pine) and other Pinus species, Pseudotsuga
menziesii (Douglas fir), Larix (larch), and Eucalyptus.
 
Distribution
This native insect occurs throughout New Zealand.
 
Economic importance
Declana floccosa is common in all New Zealand forests and ranks after two species of
Pseudocoremia (Selidosema) as the most frequently encountered looper-type caterpillar on
radiata pine and Douglas fir. However, populations are never as high as those of P. suavis
(Leaflet No.11) and the insect is of little economic importance. Only one outbreak - on Larix
decidua (European larch) at Naseby Forest, Central Otago, in 1958- has been recorded, but the
extent of the damage was not quantified.
 
Description, life history, and habits
The moth, which has a wingspan of 27-35 mm, is extremely variable in colour and patterning
(Fig.1). The forewings are rather narrow for a moth of the family Geometridae and have a
ground colour of white or grey. A series of dark- grey, occasionally brown to orange lines or dots
cross the wing, and there is usually a more or less distinct jagged line near the base of the wing
and another about one-third of the distance in from the tip. Other lines may also be present. The
hindwing is white to pale grey, often with two indistinct lines of shading near the middle and a
broad dark band at the outer edge. Thorax and abdomen are stout and generally the same colour
as the wings. The tip of the abdomen usually has a tuft of white hairs, and the underside of the
thorax is densely covered with long white hairs. The antennae of the male are comb-like while
those of the female are thread-like.
 
The moth is nocturnal and is attracted to light. During the day it is usually observed at rest on
fences and tree trunks where its mottled grey colouring causes it to closely resemble a patch of
lichen (Fig.2).

Fig. 2 - Adult of the forest semilooper at rest.  (x2)


Fig.3 Young forest semilooper caterpillar on radiata pine.  (x2.5)
 
Eggs are laid upright on the foliage of the host plant either singly or slightly attached to each
other, and in rows with up to 50 eggs in each row. The eggs, which are oval in shape and slightly
narrower at one end, are a bluish green at first but turn to dark brown in a few days and then
become reddish brown. They hatch in 10-14 days.
 
The caterpillar is a semilooper, having three pairs of thoracic legs and three pairs of abdominal
"prolegs"; only when it is very young does it arch its body when moving as much as a true
looper, which has two pairs of prolegs. There are five instars or larval stages, and colour pattern
is as variable as in the moth. The first instar is small, up to 6 mm long, and it is very difficult to
see the first pair of prolegs. The caterpillar at this stage is grey to brownish pink with various
marbling effects, but is pale red between the body segments and so appears banded (Fig.3). The
second instar is similar in colour but the red bands are not so distinct. The third instar has a pair
of warts on the upper side of the eighth abdominal segment, and minute soft projections along
the sides in line with the base of the legs. The underside of the fourth and fifth instars is
flattened, the warts are still present, and the minute soft projections on the sides of the body are
now considerably branched. These elaborately-frilled projections disrupt the outline of the
caterpillar and help to camouflage it on lichen-encrusted twigs and on foliage. Caterpillars can
vary greatly in the amount of body ornamentation, from those with a more or less smooth body,
to those of extremely rough form with small bristly warts on most segments. They can be one
colour throughout, or elaborately marbled in yellow-green, pale green, pinkish brown, brown and
pale green, or black and light grey.


Fig.4 - Fully grown forest semilooper caterpillar on Douglas fir.  (x1.5)


Fig.5 - Loose silk cocoon partly torn open to show pupa of the forest semilooper. (x2)

The fully grown caterpillar is 20-30 mm long (Fig.4) and can reach this stage within 4 weeks of
hatching. It feeds mostly at night and usually rests hidden during the day on twigs or foliage.
When fully grown the caterpillar descends to the ground on a silken thread and pupates either on
or just inside the litter layer in a loose cocoon usually incorporating dead leaf or needle
fragments (Fig.5). Pupation lasts for at least 4 weeks.
 
The life cycle of D. floccosa is not well known. Although all life forms may be found throughout
the year, evidence from light-trapping of moths and records of caterpillar abundance suggest that
there is only one main generation per year.
 
Control
No control measures have been necessary. Populations are kept in balance by natural agents such
as certain parasitic braconid and ichneumonid wasps, or by inclement weather. The tachinid fly
Pales feredayi (Hutton) is also known to parasitise the caterpillars. If insecticidal treatment were
ever required any spray recommended for leaf-eating insects should be suitable.
 
References
Hudson, G.V. 1928: "The Butterflies and Moths of New Zealand" Ferguson and Osborn,
Wellington, 386 p. 
Kay, M.K. 1982: Declana floccosa Walker (Lepidoptera: Geometridae). Forest semilooper. New
Zealand Forest Service, Forest and Timber Insects in New Zealand No. 50.
 
 
Compiled: 1982.