Life History of the Lemon Emigrant

Life History of the Lemon Emigrant (Catopsilia pomona pomona)

Butterfly Biodata:
Genus: Catopsilia Hübner, 1819
Species: pomona Linnaeus, 1775
Subspecies: pomona Linnaeus, 1775
Wingspan of Adult Butterfly: 50-70mm
Caterpillar Local Host Plants: Senna fistula (Fabaceae, common name: Golden Shower), Senna siamea (Fabaceae, common name: Kassod Tree, Siamese Cassia), Senna alata (Fabaceae, common name: Seven Golden Candlesticks).

A female Lemon Emigrant, -f. pomona.

Two male Lemon Emigrants, -f. alcmeone.

A male Lemon Emigrant, -f. hilaria.

Physical Description of Adult Butterfly:
Lemon Emigrant comes in a number of  forms for both sexes, but generally they are moderately large with wing upperside appearing in either white or yellow and black-bordered on the costa and termen of the forewing. There are two groups of forms; namely the 'crocale' group and the 'pomona' group.

• The 'crocale' group is characterized by having the upperside of antennae black, and the absence of silvery spots at cell-ends on the underside. The male -f alcmeone is mostly white above but yellow in the basal third of the wings and thinly bordered at the forewing apex. The females could appear in the jugurtha or the crocale form. The -f jugurtha is creamy white above with yellow wing base and black border on the forewing costa and termen of both wings. It has a series of black submarginal markings and a black spot at cell-end on the forewing. The -f crocale has a broad black distal border with a series of whitish spots embedded on both wings.
• The 'pomona' group is characterized by having the upperside of antennae red and the presence of red-ringed silvery spots at cell-ends on the underside. The male -f hilaria has similar upperside as the male -f alcmeone but with lesser extent of basal yellow area. The females could appear in the pomona, catilla or the nivescens form. The -f pomona has yellow wings with reduced black border and markings while -f nivescens is similar but with whitish wings. The -f catilla has large reddish patches on the underside.

A female Lemon Emigrant, -f. jugurtha.

A female Lemon Emigrant, -f. crocale.

A female Lemon Emigrant, -f. catilla.



Field Observations of Butterfly Behaviour:

The Lemon Emigrant is a common butterfly in Singapore. The fast flying adults can be found all over the island, at places such as the nature reserves, urban gardens, wastelands and housing estates. As with the other Catopsillia spp., the adults have the habit of visiting flowers and puddling on damp grounds.

A male Lemon Emigrant, -f. alcmeone.

A male Lemon Emigrant, -f. alcmeone.

A female Lemon Emigrant, -f. crocale.

Early Stages:

Across the region, the Lemon Emigrant is known to  utilize a number of host plants of the Senna genus. The most commonly utilized host plant in Singapore is the Golden Shower (Senna fistula). This plant is commonly cultivated across Singapore in gardens, parks, park connectors and even on the divider along major expressways. The caterpillars of the Lemon Emigrant feed on the relatively young leaves of the host plant.

Local host plant #1: Golden Shower (Senna fistula).

Local host plant #2: Senna siamea

A mating pair of the Lemon Emigrant (Left: female -f pomona; Right: male -f alcmeone).

Field Observations of Butterfly Behaviour:
The eggs of the Lemon Emigrant are typically laid singly on the upperside of a leaf 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 1.4-1.5mm. 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.

A mother Lemon Emigrant laying an egg on Senna alata. Left: In the act of depositing an egg. Right: Egg deposited and visible.

Left: fresh egg. Right: mature egg.

The egg takes about 2 days to hatch. The newly hatched has a length of about 2-2.2mm. It has a white head capsule bearing several short setae. Its body is creamy white with a yellowish tint 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 a newly hatched caterpillar, length: 2.2mm.

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 fast paced and the body length reaches about 4.5mm in this 1st instar which lasts about 1-1.5 days before the moult.

Two views of a 1st instar caterpillar, late in this stage, length: 4.5mm.

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. A whitish lateral band spanning the spiracles makes its debut in this instar. The 2nd instar lasts about 1-1.5 days with the body length reaching about 9mm.

Two view of a 2nd instar caterpillar, early in this stage, length: 4.8mm.

Two views of a 2nd instar caterpillar, length: 6mm.

Two views of a late 2nd instar caterpillar, dormant prior to its moult, length: 8.8mm.

The 3rd instar caterpillar resembles the 2nd instar caterpillar closely. This instar takes about 1-1.5 days to complete with body length reaching about 16mm.

Two view of a 3rd instar caterpillar, newly moulted, length: 8.6mm.

Two views of a 3rd instar caterpillar, late in this stage, length: 16mm.

Two views of a late 3rd instar caterpillar, dormant prior to its moult, length: 15.2mm.

In the 4th instar caterpillar, the whitish lateral band has a thin yellowish band lying above. Furthermore, above this yellowish band, some of the black tubercles come in much larger size than those further away, giving an impression of a black border to the whitish band. The thickness of this black border varies from specimen to specimen. This penultimate instar lasts 1.5-2 days with body length reaching about 23-26mm.

Two views of a 4th instar caterpillar, early in this stage, length: 16mm.

Two views of a 4th instar caterpillar, length: 19mm.

Two views of a late 4th instar caterpillar, dormant prior to its moult, length: 26.5mm.

The 5th instar does not usher in any significant change in the appearance. The whitish lateral band is typically broader and more prominent in this instar and the black border above it can vary from one which is very thick to one that is hardly distinguishable. This 5th instar lasts for 2.5-3 days, and the body length reaches up to 47mm.

Two views of a 5th instar caterpillar, early in this stage, length: 24mm.

Two views of a 5th instar caterpillar with thick black lateral band, length: 29mm.

Two views of a 5th instar caterpillar with a very thin black lateral band, length: 41mm.

Two views of a 5th instar caterpillar, late in this stage, length: 46mm.

On the last day of the 5th instar, the body of the caterpillar gradually shortens. 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 Lemon Emigrant on the underside of a leaf.

Another pre-pupatory larva of the Lemon Emigrant on the underside of a leaf.

A Lemon 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 blacked-tipped yellow pointed head, and its yellowish green body has a whitish yellow lateral line on each side. There is a dorsal protrusion with a thin yellow ridge line on the thorax. Length of pupae: 28-30mm.

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

Two views of a mature pupa of a female -f crocale Lemon Emigrant.

After about 5 days, the pupal skin turns translucent as the development within the pupal case comes to an end. The coloration and black borders on the forewing upperside are now discernible. The following day, the adult butterfly emerges from the pupal case.

A Lemon Emigrant butterfly emerges from its pupal case.

A newly eclosed female -f crocale Lemon Emigrant.

A newly eclosed male -f. alcmeone Lemon Emigrant.

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 Wong CM, Loke PF, Khew SK and Horace Tan