04 April 2015

Life History of the Baron v2.0

Life History of the Baron (Euthalia aconthea gurda)


Butterfly Biodata:
Genus: Euthalia Hübner, 1819
Species: aconthea Cramer, 1777
Subspecies: gurda Fruhstorfer, 1906
Wingspan of Adult Butterfly: 50-70mm
Local Caterpillar Host Plant: Mangifera indica (Anacardiaceae, common name: Mango).





Physical Description of Adult Butterfly:
On the upperside, the male is dark brown with a broad obscure post-discal band on both wings. The inner edge of this band on the forewing bears several small whitish spots. The wings typically exudes a dark purplish tinge when viewed in sidelight. The female is larger and pale bluff brown, and the white spots on its forewing are larger and well defined. On the underside, the wings are paler and have a submarginal series of black spots on both fore- and hindwings. The proboscis is lime green.






Field Observations of Butterfly Behaviour:
The Baron is common in Singapore. They are mainly found in the urban areas, wastelands or abandoned farmlands where its host plant, Mango, is/was cultivated. The adults are strong flyers. Both sexes have the habit of visiting flowers or ripened fruits (either still on the mother plant or fallen to the floor).




Early Stages:
Thus far, only one plant, Mangifera indica (Mango), has been recorded as the local host for the Baron, although it is believed that it has several other alternatives. Caterpillars of the Baron feed on leaves of the host plant, and rest on the midrib on the leaf upperside between feeds.

Local host plant: Mangifera indica (common name: Mango).

The eggs are laid singly on a leaf (either under- or upperside) of the host plant. Each egg has a hemispherical shape with a base diameter of about 2.0mm. The surface is covered with large hexagonal depressions with hair-like protuberances emerging from adjoining corners. When freshly laid, the surface is moist and in pale green. Within hours, the moisture evaporates and the color turns to a darker shade of green.

Two views of an egg of the Baron.

Two views of a mature egg of the Baron.

After about 5 days, the 1st instar caterpillar emerges and proceeds to eat the eggshell as its first meal. The caterpillar is yellowish green in body colour and has a pale yellowish brown head capsule. Its body sports ten pairs of long, yellowish and "fleshy" dorso-lateral protuberances. Black setae emanate from the body below these long protuberances and from a series of short dorsal protuberances. The caterpillar grows from an initial length of about 5mm to 7.5mm in about 2.5-3 days.

A newly hatched caterpillar, resting after devouring its egg shell, length: 5mm.

Two views of a 1st instar caterpillar, length: 6mm.

A late 1st instar caterpillar, dormant prior to the moult, length: 7.5mm.

The body of the 2nd instar caterpillar is predominantly yellowish green. All ten pairs of short protuberances seen in the 1st instar have lengthened considerably. Each is projected horizontally with numerous branched spines and is almost always pressed to the leaf surface. The protuberance is mainly pale yellowish in color. On the dorsum, white patches appear between all ten pairs of protuberances. As growth progresses in this instar, these patches become conjoined, giving the appearance of a continuous dorsal band (which helps the caterpillar to blend in the surrounding when it rests on the midrib of a leaf). The 2nd instar lasts for 2.5-3 days with the body length reaching about 11-12mm before the moult to the 3rd instar. Note that the length given here and for later instars is measured between the head and the posterior end of the last body segment, excluding the length of protuberances projected head and behind the body segments.

A 2nd instar caterpillar, early in this stage, length: 7mm.

Two views of a 2nd instar caterpillar, length: 10mm.

A late 2nd instar caterpillar, dormant prior to its moult, length: 11.5mm.

The 3rd instar caterpillar is still greenish in body color. The protuberances have all become much longer in proportion. The branched spines appear almost like a bird's feather, with the secondary spines arranged neatly around the main spine. Some of the branched spines are black. Pale purplish dorsal spots, one to each segment, rather obscure at this stage, are embedded in the yellowish dorsal band. The 3rd instar lasts for about 3 days and reaches a length of about 20mm before the next moult.

A newly moulted 3rd instar caterpillar, length: 10.8mm.

A 3rd instar caterpillar, length: 16mm.

A late 3rd instar caterpillar, dormant prior to its moult, length: 20mm.

The 4th instar caterpillar has similar appearance as in the 3rd instar. Spines on each long greenish protuberance are mostly green with the exception of the distal pair which are black with white/yellow tips. The embedded purplish spots in the dorsal band are now more distinguishable. After about 7 days in this instar, and its body length reaching 25-26mm, the caterpillar moults to the 5th instar.

A newly moulted 4th instar caterpillar..

A 4th instar caterpillar, length: 20mm.

A late 4th instar caterpillar, dormant prior to its moult, length: 25.5mm.

The 5th instar caterpillar has a close resemblance to the 4th instar caterpillar. Besides its larger size, another feature which has a observable change is the embedded purplish spots in the dorsal band. These spots are now broader and more prominent in this final instar.

A newly moulted 5th instar caterpillar, length: 24mmmm.

A 5th instar caterpillar, late in this instar, length: 34mm.

The lateral view of a 5th instar caterpillar.

A 5th instar caterpillar found on a mango leaf in the Southern Ridges.

This final instar lasts about 10-11 days with the caterpillar reaching a length of about 34mm. On the last day, the caterpillar ceases its feeding activity and its body shrinks in length. It then seeks out a spot on the underside of a leaf and stays put. There it spins large quantity of silk threads to make a silk mound, to which its posterior claspers are then attached to. Now the pre-pupa hangs from this anchor point in a head-down posture. By this time, the dorsal band has whitened entirely. Later, a short transverse pale yellowish band appears on the dorsum about mid-body.

Two views of a pre-pupa of the Baron, early in this stage.

After about 1 day of the pre-pupal stage, pupation takes place. The green pupa is suspended with its cremaster firmly attached to the silk mound. It has a smooth body which tapers steeply towards each end from a yellowish transverse dorsal ridge (which ends at the wing case with a pale biege/brown spot). The dorsal ridge is marked with four brownish spots as it runs from the transverse band to mid-thorax. Two beige/brown spots appear laterally on the mid-thorax. Furthermore, two short biege/brown cephalic horns are also featured. Length of pupae: 18-20mm.

Two views of a pupa of the Baron.

Eight days later, the pupa becomes considerably darkened, especially in the wing case area, signaling the end of the development of the adult still encased within. The next day, the adult butterfly emerges.

Two views of a mature pupa of the Baron.

The eclosion event of a Baron butterfly.

A newly eclosed Baron clinging on 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 Koh Cher Hern, Nelson Ong, Mark Wong, Anthony Wong, Loke PF, Chng CK, Khew SK and Horace Tan

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