Life History of the Tree Yellow

Life History of the Tree Yellow (Gandaca harina distanti)

Butterfly Biodata:
Genus: Gandaca Moore, 1906
Species: harina Horsfield, 1819
Subspecies: distanti Fruhstorfer, 1910
Wingspan of Adult Butterfly: 30-45mm
Caterpillar Local Host Plants: Ventilago maingayi (Rhamnaceae), Ventilago malaccensis (Rhamnaceae).

Physical Description of Adult Butterfly:

Tree Yellow has its vein 7 on the hindwing originating from well before the end of the cell. In contrast, Grass Yellow species has their rises at or just before the cell-end. On the upperside, the wings are pale lemon-yellow with a narrow black apical border on the forewing. In the female, this black border has a dentate projection along vein 4. On the underside, the wings are pale lemon-yellow without any markings.

Field Observations of Butterfly Behaviour:

The Tree Yellow is common in Singapore and can be found at multiple locations within the nature reserves. They regularly visit flowers for nectar and puddle on wet grounds for minerals.

Early Stages:

In Singapore, two plants in the nature reserves, Ventilago maingayi and Ventilago malaccensis, have been identified as larval hosts for Tree Yellow. The caterpillars feed on young leaves of the host plants. The caterpillars typically rest on the upperside of a leaf which has its leaf margin curled inwards to form a partial leaf shelter for the caterpillars.

Local host plant #1: Ventilago maingayi.

Local host plant #2: Ventilago malaccensis.

A mating pair of the Tree Yellow.

The eggs of the Tree Yellow are laid singly on a young shoot of of the host plant. The spindle shaped egg is laid standing at one end with a length of about 1.4-1.5mm. It is whitish in color and has indistinct shallow vertical ridges. The micropylar sits at the tip of the standing egg.

A mother Tree Yellow laying an egg on a young leaf of Ventilago maingayi.

An egg of the Tree Yellow on the young shoot of Ventilago maingayi.

An egg of the Tree Yellow.

The eggs take about 3-3.5 days to hatch. Each newly hatched caterpillar has a length of about 2mm and has a pale whitish head capsule. It has a cylindrical and pale whitish body covered with dorso-lateral and lateral rows of tubercles running lengthwise. As is the case for Eurema spp., each tubercle has a seta emerging from the middle of it with the tip of the seta bearing a droplet-like structure. These droplet-bearing setae is a feature seen in all five instars of the larval phase.

Two views of a newly hatched caterpillars of the Tree Yellow, length 2mm.

After hatching, the young caterpillar does not seem to follow the common habit of eating the empty egg shell for its first meal, instead it moves away to feed on the leaf lamina. The body colour turns pale yellowish brown as growth progresses. The body length reaches about 4mm in about 2 days before the moult to the 2nd instar.

Two view of a 1st instar caterpillar, length 2.5mm.

The body of the 2nd instar caterpillar is pale whitish to yellowish with a greenish tinge. Its head capsule is similarly coloured. This instar lasts about 2 days with the body length reaching about 7mm.

Two views of a 2nd instar caterpillar, early in this instar, length 3.5mm.

Two views of a 2nd instar caterpillar, length: 5mm

The 3rd instar caterpillar resembles the 2nd instar caterpillar closely with the body bearing a stronger greenish tinge than in the 2nd instar. This instar takes about 2 days to complete with body length reaching about 9-10mm.

Two views of a 3rd instar caterpillar, length: 8.8mm.

Two views of late 3rd instar caterpillar, dormant prior to its moult, length: 9.5mm.

A 3rd instar caterpillar of the Tree Yellow found in the central catchment reserve.

The body of the 4th instar caterpillar is little changed in appearance from its previous instars, with its body coloration more whitish overall. This penultimate instar takes about 2-3 days to complete with body length reaching about 16-17mm.

Two views of a newly moulted 4th instar caterpillar.

Two views of a 4th instar caterpillar, length: 12mm.

Two views of a late 4th instar caterpillar, dormant prior to its moult, length: 16mm.

A 4th instar caterpillar of the Tree Yellow found in the central catchment reserve.

The 5th and final instar does not bring along any drastic change in appearance in both the body and head capsule. Overall the caterpillar is more yellowish green than in the previous instars. The 5th instar lasts about 3-4 days, and the body length reaches up to 24-25mm.

A newly moulted 5th instar caterpillar of the Tree Yellow.

Two views of a 5th instar caterpillar, early in this stage, length: 19mm.

Two views of a 5th instar caterpillar, late in this instar, length: 24.5mm.

Two views of a late 5th instar caterpillar, ceased feeding and ready to become a pre-pupa.

On the last day of the 5th instar, the body of the caterpillar shortens and the body colour changes to pale yellowish jade green. It ceases feeding and comes to a halt on the underside of a leaf or a stem of the host plant. Here the caterpillar spins a silk pad and a silk girdle. With its posterior end secured to the silk pad via claspers, and the body suspended at the mid-section with the girdle, the caterpillar soon becomes immobile in this pre-pupatory pose.

The sad ending of a final instar caterpillar of the Tree Yellow. Here the parasitoid larvae had emerged from the caterpillar and pupated, leaving the caterpillar to die hours later.

A late 5th instar caterpillar of the Tree Yellow found in the central catchment reserve.

A pre-pupatory larva of the Tree Yellow.

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 the cremaster replacing claspers in attaching the posterior end to the silk pad, It has a pointed cephalic horn) and a slightly keeled wing pad, and its body is free of any spots/markings. The body colour is pale green throughout with the abdomen in paler green. Length of pupae: 17-19.5mm..

Two views of a pupa of the Tree Yellow.

Two views of a mature pupa of the Tree Yellow.

After about 4 days of development, the pupal skin turns translucent as the development within the pupal case comes to an end. The yellow coloration and back borders on the forewing upperside are now discernible. The following day, the adult butterfly emerges from the pupal case.

A newly eclosed Tree Yellow clinging onto its empty 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 James Chia, Lemon Tea YK, Nelson Ong, Mark Wong, Loke PF, Simon Sng, Frederick Ho, Sunny Chir and Horace Tan