17 May 2014

Life History of the Gram Blue

Life History of the Gram Blue (Euchrysops cnejus cnejus)

Butterfly Biodata:
Genus: Euchrysops Butler, 1900
Species: cnejus Fabricius, 1798
Subspecies: cnejus Fabricius, 1798
Wingspan of Adult Butterfly: 20-26mm
Caterpillar Local Host Plants: Pueraria phaseoloides (Fabaceae/Leguminosae, common name: tropical kudzu), Vigna reflexopilosa (Fabaceae/Leguminosae, common name: creole bean).

The upperside view of a female Gram Blue.

Physical Description of Adult Butterfly:
On the upperside, the male is pale purple and with tornal spots in spaces 1b and 2 of the hindwing thinly crowned in orange. The female has a brown border on both wings and is pale shining blue in the basal area, and its hindwing has submarginal spots bordered with a dark sinuate line and larger and more prominent orange-crowned tornal spots in spaces 1b and 2. On the underside, both sexes are pale buff with a series of marginal, submarginal and post-discal spots, all pale brown and white-bordered. In the hindwing, there are three black basal spots, one black costal spot, two orange-crowned tornal spots in spaces 1b and 2 which are edged with metallic green scales and a white-tipped tail at the end of vein 1b.

The upperside view of a male Gram Blue.

Field Observations:
Gram Blue is moderately common in Singapore. Its distribution is rather localized and at times they can be locally abundant in wastelands or trail side where its host plants, the tropical kudzu and the creon bean, are growing as weeds. In the early morning and late afternoon sun, both sexes are often seen sunbathing on leaves with open wings. The adults have the habit of visiting flowers of various weeds for nectar.

Early Stages:
So far, only two host plants, Pueraria phaseoloides and Vigna reflexopilosa, have been recorded as the local larval host for Gram Blue. The caterpillars feed on young leaves, seed pods and flowers of these host plants.

Local host plant #1:Pueraria phaseoloides.

Local host plant #2:Vigna reflexopilosa.

A mating pair of the Gram Blue.

The eggs are laid singly on a young shoot or a flower bud of the host plant. Each egg is about 0.6mm in diameter, and whitish with a strong greenish undertone. It is discoid-shaped with a depressed micropylar at the center of the upper surface. The egg surface is reticulated with a fine pattern of ridges and indentations which are larger along the rim of the upperside.

Two views of an egg of the Gram Blue.

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

It takes about 2.5 days for the egg to hatch. The newly hatched has a black head and a pale yellowish body with a length of about 1mm. The body also features long setae dorso-laterally and along the body fringe. After about 2.5-3 days of growth in the first instar, and reaching a length of about 2.2mm, the caterpillar moults to the next instar. Towards the end of the 1st instar, the caterpillar develops yellowish dorsal band, and dorso-lateral bands.

Two views of a 1st instar caterpillar, length: 2mm.

Two views of a late 1st instar caterpillar, dormant prior to its moult, length: 2mm.

In the 2nd instar, there are numerous short and fine setae covering the body surface. The head is still black in color. The caterpillar is either yellowish green or pale yellowish brown with dorso-lateral and dorsal bands. At this stage, the dorsal nectary organ is present but indistinct. The 2nd instar caterpillar reaches a length of about 4mm, and after about 3 days in this stage, it moults again.

Two views of a 2nd instar caterpillar, early in this stage, length: 2.2mm.

Two views of a late 2nd instar caterpillar, dormant prior to its moult, length:3.5mm.

Compared to the 2nd instar caterpillar, the 3rd instar caterpillar bears a denser coat of short setae on its yellowish green body. The narrow and dark dorsal band is bordered with white bands on both sides, and there are oblique whitish stripes protruding from the dorsum to eitehr sides. The dorsal nectary organ and the pair of tentacular organs, on the 7th and 8th abdominal segments, are now readily observed. The 3rd instar takes about 3 to 3.5 days to complete with the body length reaching about 7-7.5mm.

Two views of a 3rd instar caterpillar, early in this stage, length: 4mm.

Two views of a 3rd instar caterpillar, with part of its head in the seed pod (at the right), length: 6mm.

Two views of a late 3rd instar caterpillar, dormant prior to its moult, length: 6mm.

The 4th instar caterpillar has a dense coat of short setae all over the body surface. The body coloration could be entirely green or pale yellowish green. In some specimens, short reddish strips can be seen along the dorsal line. The oblique lateral markings seen in the 3rd instar are still present but rather indistinct.

Two views of a 4th instar caterpillar, early in this stage, length: 8mm.

Two 4th instar caterpillars, lengths: 12.5mm (top, pale yellowish green) and 13.5mm (bottom, green).

A 4th instar caterpillar attended by a small ant, note the extruded tentacular organs nearby.

After about 4-5 days of feeding in the 4th instar and reaching a length of about 14mm, the caterpillar stops food intake and seeks out a pupation site. During this time, its body gradually shrinks and turns uniformly green. Typically the caterpillar chooses a spot on a leaf for its pupation site. The pre-pupatory caterpillar prepares for pupation by spinning a silk girdle and a silk pad to which it attaches itself via anal claspers.

Two views of a pre-pupa of the Gram Blue, already girdled down.

After about 1 day as a pre-pupa, pupation takes place. The pupa is predominantly yellowish green to green and has a fair number of small black spots/specks over its body surface, arranged in a symmetrical manner about the dorsal line. The pupa has a typical lycaenid shape. There are short whitish fine setae on its body and at the anterior end. Pupal length: 10-10.5mm.

Two views of a pupa of the Gram Blue.

5 to 5.5 days later, the pupa turns dark, first in the wing pad and thorax, then progressively in the abdomen. The extent of the bluish patch in the wing pads gives an early indication of the gender of the soon-to-emerge adult. The next day, the pupal stage comes to an end with the emergence of the adult butterfly.

Two views of a mature pupa of a male Gram Blue.

A newly eclosed Gram Blue.

  • [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 Bobby Mun, Benedict Tay, Goh Lai Chong, Jonathan Soong, Koh Cher Hern, Simon Sng, Ben Jin Tan, Federick Ho, Khew SK and Horace Tan.


Unknown said...

Good posting.

Unknown said...

Very nicely explained with pictures!