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The Cossidae are a relatively small family that is most diverse in the tropics
and subtropics. There are 34 species in Borneo but only 7 in Japan (Inoue et
al. 1982). Two subfamilies have been recognised in the Oriental fauna, the
Cossinae and Zeuzerinae.
The larvae bore in the twigs and trunks of bushes and
trees and thus a number of species come into conflict with man, attacking timber
and fruit trees as well as bush crops such as cocoa, coffee and tea.
There have been two accounts of Oriental Cossidae
published relatively recently. Roepke (1957) monographed the species of Malaysia
and western Indonesia whilst Arora (1976) has treated the Indian fauna.
Adult
characteristics
The adult moths are usually large with elongate, slender forewings and
much shorter hindwings. The wing markings are usually cryptic, bark-like,
involving fine dark striae or reticulation. The abdomen is long, reflecting the
length of the forewings.
The male antennae are usually unipectinate or bipectinate. In the
Zeuzerinae they are broadly bipectinate over the basal half and almost filiform
distally, but a variety of structure is seen within the genus Cossus:
filiform, unipectinate, bipectinate.
The wing venation is illustrated in Figs. 3-5. The stem of vein M is
present and branches within the cells of both, wings. In Cossus the
forewing has a small, narrow areole from which vein M1 arises at a
point well separate from the cell (Fig. 3) whereas in the Zeuzerinae the areole
is large, broadly triangular, with M1 arising from where its
posterior angle abuts onto the cell. In the hindwing of Zeuzera vein Sc
is associated with the cell (Fig. 4) whereas in other Oriental cossids it is
free.
The frenulum is present, but mechanical interaction between the narrow
wings is also brought about through overlap between the two, a convexity to the
dorsum of the forewing overlying an expansion of the humeral area (Cossus) or
a central convexity of the anterior margin (Zeuzerinae) of the hindwing.
The two subfamilies differ in characters of the hind-tibiae (Arora
1976). These are dilated in the Cossinae and bear two pairs of spurs, but are
slender in the Zeuzerinae and have only one pair of spurs. In Xyleutes and
Zeuzera the arolium is lost, but not in the Cossinae, Phragmataecia and
Azygophleps (Arora).
In the male genitalia the uncus is usually broad and well developed. The
gnathi are linked by the characteristic scobinate, usually bilobed bulla in Cossus
(Roepke 1957), but occur as weak, separate, long and slender sclerotised
bands (lori) in the Zeuzerinae, though they are absent in Phragmataecia. The
valves in Cossus each have a basal spine and are linked by fusion of this
with the juxta; a scobinate process associated with the juxta basally and
sacculus ventrally, just ventral to the basal spine, may be homologous with the
ligula of the Zeuzerinae. The juxta in the Zeuzerinae is not so fused and has
simple lateral processes (the ligulae of Roepke) that extend dorsally on either
side of the aedeagus. The aedeagus is a simple rod in Cossus but in most
zeuzerines it is broad, short, apically deeply cleft into dorsal and ventral
longitudinally corrugate 'jaws'.
The female genitalia have the ovipositor lobes, eighth segment and the
apodemes/apophyses of both exceedingly elongate and slender (Fig. 67). This
slender ovipositor can often be seen extended in dried specimens and may be a
modification for insertion of eggs into crevices in bark.
Arora (1976) presented a phylogeny showing the relationships between the various genera in the Indian fauna. The divisions were usually based
on two states of a character, one of which is probably a plesiomorphy, hence the
morphological basis for his phylogeny is unsatisfactory. The definition of
genera within the Zeuzerinae also requires further investigation as will be
discussed below. The adult characters that show promise of apomorphy and may be
valuable in the definition of the two subfamilies, at least in the Old World
fauna, are, for the Cossinae, a dilated hind-tibia, a gnathus with a bulla, and
a basal spine to the valve, and, for the Zeuzerinae, loss of one pair of spurs
on the hind-tibia, a central dilation to the anterior margin of the hindwing,
partially bipectinate male antennae, and a cleft apex to the aedeagus.
Larval characteristics
Cossid larvae have characteristics that reflect their mode of life (Fracker
1915): wood and stem boring. The head is broad, longer than wide, and the
mandibles are large. The pinacula are heavily chitinised but the setae are
relatively reduced. The prothorax bears a distinctive plate or shield that has
the caudal margin smooth on Cossus but its dorsal half conspicuous and
strongly rugose in the Zeuzerinae. All prolegs are present, the crochets
arranged in a complete circle.
Gardner (1945) described larvae of a few of the Indian species and also
noted this difference of the prothoracic shield. Within the Zeuzerinae, Azygophleps
has the prothoracic rugosity relatively fine and even whereas in Zeuzera and
Xyleutes the rugosity is much coarser anteriorly. The crochets are
uniordinal in Azygophleps but biordinal or triordinal in Zeuzera and
Xyleutes.
Habitat preference
The species are almost entirely restricted to, or most common in,
lowland forests. Some Cossus species may be preferentially montane, and Zeuzera
lineata has also been recorded mainly from montane forests.
There is some tendency, particularly in Zeuzera and Xyleutes, for
species to be most common in ‘inundated' forests: alluvial, swamp and
mangrove. Inundation is periodic but it is likely that such habitats have lower
termite diversity than forests where the floor is never flooded. Such low
diversity has been observed in alluvial forest by Collins (1979) though wood
feeding species were not so affected as litter feeding ones. Cossidae may
therefore experience less competition for standing timber and moribund trees in
such habitats.
Zoogeography
The genus Cossus does not extend to Australasia, and Oriental
species are geographically much more localised than in the other genera. Borneo
at present has the highest recorded diversity for the genus in the Oriental
tropics. Zeuzera and Xyleutes include 40% of species widespread
through the Indo-Australian tropics, 45% Sundanian or more widely Oriental
species and only three species (15%) are endemic to Borneo. The genus Phragmataecia
has not been recorded from Borneo but is diverse in India (Arora 1976) and
known from Sumatra and Java (Roepke 1957).
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