View Image Gallery of Family Cossidae

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.

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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