Chlenias auctaria

Chlenias auctaria Guenée, 1857
DIPTYCHINI, ENNOMINAE, GEOMETRIDAE, GEOMETROIDEA

Don Herbison-Evans
(donherbisonevans@yahoo.com)
and
Stella Crossley

Chlenias auctaria
early instar
(Photo: courtesy of Abby Phillips, Caulfield South, Victoria)

This Caterpillar has a complex pattern of coloured lines. Early instars have a dorsal yellow stripe. Each side of this are three broad black lines, each separated by a thin yellow stripe. The pair of black lines next to the dorsal yellow stripe contains three fractured thin white lines. The other two broad black lines contain two fractured thin white lines. The ventral pair meet under the caterpillar, and are separated by a narrow central ventral yellow line.

close-up of head and thorax
(Photo: courtesy of Abby Phillips, Caulfield South, Victoria)

The head capsule and anal plate are blue-green speckled with grey. The final abdominal segment deveops a similar colour and pattern to that of the head, no doubt confusing some predators into attacking the less important end first. The true legs are red, and there is a red splodge on each penultimate proleg.

Later instars develop a wide gray line along the middle of the dorsal yellow stripe, and later still that becomes split by a narrow white line. The three black lines along each side become black, green, and black, and their regular white markings degenerate into wiggles.

later instar
(Photo: courtesy of David Akers, Won Wron, Victoria)

This caterpillar has been recorded as feeding on over 17 species of unrelated plants, including:

Boneseed ( Chrysanthemoides monilifera, ASTERACEAE ),

Wattles ( Acacia, MIMOSACEAE ),

Gum Trees ( Eucalyptus, MYRTACEAE ),

Monterey Pine ( Pinus radiata, PINACEAE ),

Needlewood ( Hakea, PROTEACEAE ),

Cherry Ballart ( Exocarpos cupressiformis, SANTALACEAE ), and

Purple Coral Pea ( Hardenbergia violacea, VIOLACEAE ).

It has adapted so well to feeding on the introduced Monterey Pine that it has become an occasional pest in pine plantations.

The species has been studied to discover how and why it is so polyphagus. It was found that the mean pupal size of was significantly reduced by feeding on Pinus radiata (a non-native plant host) compared to two native host plants (Eucalyptus obliqua and Acacia mearnsii). The main reason for this seemed to be the higher ratio of dry weight to wet weight of plant material in the native plants compared to the introduced plant species; the larvae on Pinus radiata simply could not get enough nutrient to catch up to those feeding on the native plant species. So given that it develops poorly on such plants, why does it continue to use them for food?

It appears that the polyphagous nature of this species may be related to the dispersal behaviour in this group. First instar larvae are active dispersers, and spend the first two days of their life moving about by climbing to the top of the plant upon which the eggs were laid, spinning a silk balloon, then ballooning to other plants. The choice made by adult female moths appears to have little effect on the host that the larvae end up eating. Larvae must feed within two days of dispersal; whatever plant they end up on at the end of two days dispersal becomes their food plant, hence the ability to cope with eating very different host plants appears to be an adaptation to this mode of dispersal.

male, drawing by Achille Guenée, Uranides et Phalénites,
Histoire naturelle des insectes; spécies général des lépidoptères,
Volume 9, Part 10 (1857), plate 14, fig. 1,
Image courtesy of Biodiversity Heritage Library, digitized by Smithsonian Libraries.

The adult moths are grey with variable darker markings on the forewings.

female
(Photo: copyright Dave Britton)

Adult females do not fly very far from where they emerge from pupae, and lay large egg masses (around 200 eggs) on the top of plants. The eggs are oval and finely dimpled all over. They are initially white, but turn purple as they approach hatching.

eggs, magnified
(Photo: copyright Cathy Byrne)

The species is found in

Tasmania, and

The adult moths of the various species in the genus Chlenias are all very variable, and appear to be more variable than the variations between the species. The identification of the specimens pictured here may prove to be wrong when more work is done on this genus.