06 December 2014

Life History of the Dark Brand Bush Brown

Life History of the Dark Brand Bush Brown (Mycalesis mineus macromalayana)


Butterfly Biodata:
Genus: Mycalesis Hübner, 1818
Species: mineus Linnaeus, 1758
Subspecies: macromalayana Fruhstorfer, 1911
Wingspan of Adult Butterfly: 40-45mm
Caterpillar Local Host Plants: Axonopus compressus (Poaceae, common names: Wide-leaved Carpet Grass, Cow Grass), Paspalum conjugatum (Poaceae, common names: Buffalo Grass, Hilo Grass).




Physical Description of Adult Butterfly:
On the upperside, the wings are dark greyish  brown with a large but obscure ocellus in space 2 of the forewing, and rarely any ocellus on  the hindwing. The male has a small, dark brown sex brand in space 1b of the forewing, and another one at vein 7 of the hindwing overlaid with a pale yellow hair tuff. On the underside, both wings are paler brown in ground colour and have a clear-whitish post-discal band. There is a series of ringed ocelli in the submarginal area on both wings. In the forewing, the submarginal ocelli usually include only one ocellus in each of spaces 2 and 5, with the former being much larger.  In the hindwing, there is a thin, dark indentation line  stretching down to (but not beyond) vein 1b. Furthermore, the  lower 4 ocelli in the hindwing (in spaces 1b, 2 and 3) are more or less aligned.



Field Observations of Butterfly Behaviour:
The Dark Brand Bush Brown is a common butterfly in Singapore. Adults are typically sighted flying in and around grassy patches at multiple locations across the island. As with other Satyrinae members, the adults fly in an erratic and jerky manner as their wings are closed for a relatively long period during flights.





Early Stages:
Two common grass species, Axonopus compressus and Paspalum conjugatum, have been recorded as larval hosts for the Dark Brand Bush Brown in Singapore so far. The caterpillars feed on leaves of the host plant, and have been observed to forcefully ejecting their frass pellets, a larval habit rarely seen outside the skipper/flat families. They tend to rest lengthwise on the underside of a leaf during pauses between feeds.

Dark Brand Bush Brown caterpillars in the act of catapulting frass pellets.

Local host plant #1: Axonopus compressus.

Local host plant #2: Paspalum conjugatum.

A mating pair of the  Dark Brand Bush Brown.

The eggs are laid singly on the underside of a grass blade. Each spherical egg (about 1.1mm in diameter) is pale translucent with a light greenish tinge. The surface appears to be smooth to the naked eyes, but is actually sculptured with a hexagonal reticulum when viewed with a macro lens.

A mother Dark Brand Bush Brown laying an egg on a blade of Axonopus compressus.

Two views of an egg of the Dark Brand Bush Brown .

Two views of a mature egg with the head clearly visible through the egg shell.

The egg takes about 3 days to hatch. The young caterpillar nibbles away a portion of the egg shell to exit and then proceeds to devour the rest of the egg shell almost entirely. It has a cylindrical body in whitish colour, and an initial body length of about 3.2mm. The body is covered with dorso-lateral and lateral rows of whitish setae. At the posterior end, there is a pair of backward-pointing processes. Its dark colored head features a number of setae and has a pair of short and rounded horns and a few lateral protuberances.

Two views of a newly hatched caterpillar, length: 3.1.mm

As a result of its leaf diet, the 1st instar caterpillar soon takes on a strong greenish undertone. As growth proceeds, the dorsum of the last two to three segments turns reddish. The first instar lasts about 2.5-3 days with the body length increases to about 6-6.5mm.

Two views of a 1st instar caterpillar, length: 5.5mm.

Two views of a late 1st instar caterpillar, dormant prior to its moult, length: 6mm.

In the 2nd instar, the cephalic horns become pointed and the two anal processes longer and thus pronounced. The few lateral conical protuberances on the head capsule are now much smaller and whitish in colour. The body is yellowish green. The head and body is also adorned with numerous minute tubercles, each with a single seta emanating from it. The 2nd instar lasts about 3 days with the body length reaches about 9.8mm.


Two views of a 2nd instar caterpillar, early in this stage, 7mm.

Two views of a 2nd instar caterpillar, length: 9.3mm.

Two views of a late 2nd instar caterpillar, dormant prior to its moult, length: 9mm.

The 3rd instar caterpillar mostly resembles the previous instar. The head capsule is dark brown in the cephalic horns and the basal areas around the mouth parts but pale brown elsewhere. This stage also takes 3 days to complete with body length reaching about 16-16.5mm.

Two views of 3nd instar caterpillar, early in this stage, length: 9.8mm.

Two views of a 3nd instar caterpillar, length: 14mm.

Two views of a late 3nd instar caterpillar, dormant prior to its moult, length: 15.5mm.

The 4th instar caterpillar bears a close resemblance to the 3rd instar caterpillar with no obvious change of any features or markings. The 4th instar lasts about 4 days with body length reaching about 23-25mm.

Two views of a newly moulted 4th instar caterpillar, length: 14.9mm.

Two views of a late 4th instar caterpillar, dormant prior to its moult, length: 19.5mm.

Two views of a late 4th instar caterpillar, dormant prior to its moult, length: 24.5mm.

The next moult brings the caterpillar to its 5th and final instar. Now the caterpillar could appear in two colour forms: a brown form which is mostly pale to dark reddish brown and a yellow form which is pale yellowish green. Feature wise, there is now a narrow band on the dorsum of the thorax. In addition, small black dorso-lateral spots appear at the joints between segments 2 to 7. Furthermore, faint oblique stripes adorns the body surface. Initially the head capsule bears similar markings to the previous instar, but this turns increasing dark to black as growth progresses. In a period of about 6 days, the body grows to a maximum length of about 40-41mm.

Two views of a 5th instar caterpillar, yellow form, length: 24mm.

Two views of a 5th instar caterpillar, brown form, length: 32mm.

Two views of a 5th instar caterpillar, brown form, late in this stage, length: 37mm.

Two views of a 5th instar caterpillar, brown form, late in this stage, length: 36mm.

Toward the end of the 5th instar for both colour forms, the body gradually shrinks in length and turn mostly yellowish green. Typically, the caterpillar will seek out a spot on the underside of a leaf blade to spin a silk pad. It then anchors itself there via its anal end, and assumes its upside-down pre-pupatory pose.

Two views of a 5th instar caterpillar, late in this stage, body shortened and body colour changed to mostly green.

A prep-pupa of the Dark Brand Bush Brown.

After one day as a pre-pupa, pupation takes place. The smooth pupa is mostly green throughout. It is somewhat angular in appearance, with a dorsal keel on the thorax and ridges defining the dorsal wing margins. There are a few small black spots dotting the wing pad margin. Dorso-lateral pairs of small whitish spots can be observed on abdominal segments 2-6. Length of pupae: 15-16mm.

A Dark Brand Bush Brown caterpillar moults to its pupal stage.

Three views of a pupa of the Dark Brand Bush Brown.

After 5.5-6 days of development, the pupa becomes darkened in color, and the ringed-spot on the forewings can now be seen through the pupal skin in the wing pads. The next day the eclosion event takes place with the adult butterfly emerges to start the next phase of its life cycle.

Three views of a mature pupa of Mycalesis persoides.

A newly eclosed Dark Brand Bush Brown.

References:
  • [C&P4] The Butterflies of The Malay Peninsula, A.S. Corbet and H.M. Pendlebury, 4th Edition, Malayan Nature Society.
  • 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 Bobby Mun, L C Goh, Loke PF, Frederick Ho, Khew SK and Horace Tan

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