26 October 2013

Life History of the Orange Emigrant

Life History of the Orange Emigrant (Catopsilia scylla cornelia)


Butterfly Biodata:
Genus: Catopsilia Hübner, 1819
Species: scylla Linnaeus, 1763
Subspecies: cornelia Fabricius, 1787
Wingspan of Adult Butterfly: 50-60mm
Caterpillar Local Host Plant: Senna surattensis (Fabaceae).


An Orange Emigrant taking nectar from a flower.

A male Orange Emigrant displaying its upperside.

A close-up view of the head of an Orange Emigrant.

Physical Description of Adult Butterfly:
On the upperside, the forewing is white with a black border and the hindwing is deep chrome-yellow. In addition, the female has a black post-discal fascia on the forewing and a series of black marginal spots on the hindwing. On the underside, the wings are yellow with intermittent, faint brown post-discal spots. A brown ring marking can be found at the cell-end on both wings.





Field Observations of Butterfly Behaviour:
The Orange Emigrant is considered a common butterfly in Singapore, though its occurrence is rather localized. The fast flying adults are typically found in parks, park connectors and gardens where its local host plant, Senna surattensis, is cultivated. As with the other Catopsillia spp., the adults have the habit of visiting flowers and puddling on damp grounds.



A close-up view of a portion of the hindwing showing the diffuse post-discal fascia is composed of loosely scattered brown scales.

Early Stages:
Across the region, the Orange Emigrant has several host plants in the Senna genus, including S. fistula (The Golden Shower). However the popular host plant in Singapore, and the only one found utilized so far, is Senna surattensis. This plant is commonly cultivated across Singapore in gardens, parks, park connectors and even on the divider along major expressways. The caterpillars of the Orange Emigrant feed on the leaflets of the host plant. At times, one could find numerous Orange Emigrant caterpillars feeding on the same plant, causing a serious degree of defoliation as a result.

Local host plant: Senna surattensis

A mating pair of the Orange Emigrant.

The eggs of the Orange Emigrant are typically laid singly on the upperside of a leaflet of the host plant. At times, more than one egg can be found on the same leaflet. The long spindle shaped egg is laid standing at one end with a length of about 1.8-1.9mm. It is white in color with vertical ridges and numerous indistinct and intermittent horizontal ridge lines. The micropylar sits at the tip of the standing egg.

Left: A mother Orange Emigrant laying an egg on a leaflet. Right: The mother butterfly took off, giving a view of its upperside and the egg laid (indicated by the red arrow).

Left: fresh egg. Right: mature egg showing the mouth part near the top.

The egg takes about 2 days to hatch. The newly hatched has a length of about 2.4mm. It has a white head capsule bearing several short setae. Its body is creamy white and featuring dorsal, dorso-lateral and lateral rows of small tubercles running lengthwise. Each tubercle has a short seta emerging from the middle of it.

Two views of newly hatched caterpillar eating the remnant of its egg shell.

After hatching, the young caterpillar proceeds to devour the remnant of the egg shell. The leaf diet will soon follow, and with that the body turns yellowish green. The growth is moderately fast paced and the body length reaches about 4.7mm in this 1st instar which lasts about 2 days before the moult.

Two views of a 1st instar caterpillar, length: 3.7mm.

Two views of a late 1st instar caterpillar, dormant prior to its moult, length: 4.8mm.

The 2nd instar caterpillar is yellowish green on all body segments and the head. The body is covered in rings (about five for each body segment) of numerous small dark tubercles from which very short setae emerge. The head capsule also features numerous similar tubercles. This instar lasts about 2 days with the body length reaching 7-8mm.

Two view of a 2nd instar caterpillar, length: 7mm.

Two views of a late 2nd instar caterpillar, dormant prior to its moult, length: 8mm.

The 3rd instar caterpillar resembles the 2nd instar caterpillar closely. This instar takes about 2 days to complete with body length reaching about 11-12mm.

Two view of a 3rd instar caterpillar, newly moulted, length: 8mm.

Two views of a 3rd instar caterpillars, length: 10.5mm.

A white to yellowish band running across the spiracles appears in the 4th instar caterpillar. Above the line, some of the black tubercles blanketing the body surface are larger than the rest, but these do not appear in great numbers to give an appearance of a dark band (as in the case for the Lemon Emigrant and the Mottled Emigrant). This penultimate instar lasts 2 days with body length reaching about 22-23mm.

Two views of a 4th instar caterpillar, early in this stage, length: 12.5mm.

Two views of a 4th instar caterpillar, length: 15mm.

The 5th instar does not usher in any significant change in appearance of the caterpillar. Now the dark tubercles covering the body surface are proportionately smaller, and the lateral white-yellow bands are more prominently featured. This 5th instar lasts for 4-5 days, and the body length reaches up to 40-42mm.

Two views of a 5th instar caterpillar, early in this stage, length: 21mm.

Two views of a 5th instar caterpillar, late in this stage, length: 38mm.

A 5th instar caterpillar sighted in a local university campus.

On the last day of the 5th instar, the body of the caterpillar shortens and changes to a dull shade of pale green. It ceases feeding and comes to rest on the midrib on the underside of a leaflet or the stem/stalk on the host plant. Here the caterpillar spins a silk pad and a silk girdle to secure itself and then becomes immobile in its pre-pupatory pose.

A pre-pupatory larva of the Orange Emigrant on the underside of a leaf stalk.

An Orange Emigrant caterpillar moults to its pupal stage.

Pupation takes place about 0.5-1 day later. The pupa secures itself with the same silk girdle as in the pre-pupal stage, but with a cremaster replacing claspers in attaching its posterior end to the silk pad on the stem. The pupa has a pointed head, and its yellow to yellowish green body has a bright yellow lateral line on each side. There is a dorsal protrusion with a yellow ridge line on the thorax. The keel formed by the tapering wing case is much less pronounced than those seen in the Eurema spp. Length of pupae: 25-26mm.

Two views of a pupa of the Orange Emigrant, dull yellowish green in colour.

Two views of a pupa of the Orange Emigrant, bright yellowish green in colour.

A pupa of the Orange Emigrant found on a S. surattensis plant in a local university campus.

Two views of the mature pupa of a male Orange Emigrant.

Two views of the mature pupa of a female Orange Emigrant.

After about 6 days of development, the pupal skin turns translucent as the development within the pupal case comes to an end. The yellow coloration and black borders on the forewing upperside are now discernible. The following day, the adult butterfly emerges from the pupal case.

An Orange Emigrant butterfly emerges from its pupal case.

A newly eclosed Orange Emigrant resting near its pupal case.

References:
  • [C&P4] The Butterflies of The Malay Peninsula, A.S. Corbet and H.M. Pendlebury, 4th Edition, Malayan Nature Society, 1992.
  • Butterflies of Thailand, Pisuth Ek-Amnuay, 2nd Edition, 2012.
  • A Field Guide to the Butterflies of Singapore, Khew S.K., Ink On Paper Communications, 2010.
Text by Horace Tan, Photos by Henry Koh, Brian Goh, Koh Cher Hern, Nelson Ong, Anthony Wong, Tan Ben Jin, Federick Ho, Sunny Chir and Horace Tan

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