Life History of the Acacia Blue (Surendra vivarna amisena)
Butterfly Biodata:
Genus: Surendra Moore, 1881
Species: vivarna Fabricius, 1793
Sub-species: amisena Fruhstorfer, 1912
Wingspan of Adult Butterfly: 28-32mm
Caterpillar Local Host Plants: Falcateria moluccana (Leguminosae, common name: Albizia), Parkia speciosa (Leguminosae, common name: Petai), Saraca thaipingensis (Leguminosae, common name: Yellow Saraca), Archidendron jiringa (Leguminosae, common name: Jering), Mimosa pigra (Leguminosae, common name: Giant Sensitive Tree).
Physical Description of Adult Butterfly:
Above, the male is shining purplish blue with broad black apical border on the forewing and broad black borders on the costal and inner margins of the hindwing. The female is steely blue with thin black borders on both wings. Underneath, both sexes are brown with an irregular dark brown post-discal line on both wings but with that on the hindwing outwardly edged with white. Both wings have a series of dark submarginal striae and a dark rounded submarginal spot is present in space 6 of the hindwing. Both wings have a more obscure sub-basal series of dark striae with the striae in space 7 of the hindwing inwardly edged in white. The hindwing has a white-tipped tail at vein 2, and a tooth at vein 3, both being longer in the female than in the male. There is an obscure dark tornal spot and another similar marginal spot in space 2 on the hindwing, with metallic bluish green scalings overlay these spots and covering the marginal/sub-marginal space between these two spots.
Field Observations of Butterfly Behaviour:
The Acacia Blue is relatively common in Singapore. The adults can be sighted in forested areas within the nature reserves and wastelands, and occasionally in urban parks and gardens. They have a a rapid flight and can be observed to sun-bathe with fully open wings in sun-lit conditions. A good opportunity to photograph the skittish adults is when they visit the ripening fruits of the Singapore Rhododendron for their energy intake. The females are more likely to be seen in the vicinity of their host plants.
Early Stages:
The immature stages of Acacia Blue are polyphagous. To date 5 plants in Leguminosae have been recorded as its local hosts. Caterpillars of all instars feed on young leaves of the host plants, and are fond of imbibing nectary fluid from the glands occuring on the petiole and rachis of the host plants. In the field, the caterpillars live in association with ants visiting the same plants for nectary intake. However, in home breeding settings, the caterpillars have no problem reaching adulthood in the absence of ants.
Eggs are laid on the underside of a young leaf or other parts of a young shoot of the host plant. The egg is whitish with a green undertone and is about 07-0.8mm in diameter. It is shaped like a slightly flattened chinese bun with the surface is reticulated with interconnecting ridges which raise sharply at the intersections. As is typical, the depressed micropylar is found in the polar region.
Each egg takes about 3 days to hatch. The young caterpillar emerges after nibbling away sufficiently large upper portion of the egg shell. Measured at a length of about 1.3-1.4mm, its dark yellow body bears lateral brown patches. Long white-tipped dark setae occur dorso-laterally and whitish long setae along the peripheral rim of the body. Its head capsule is dark brown to black, and both its prothoracic shield and anal plate are colored as per the body base colour.
As the caterpillar feeds and grows, the body base colour becomes paler yellow with a strong green undertone. This instar lasts for about 3 days with the body length reaching up to 3mm.
Covered with numerous short setae, the body of the 2nd instar caterpillar is yellowish green with obscure white oblique stripes occurring laterally. The prothoracic shield is marked with two vertical dark stripes, and the head capsule has changed to a pale yellowish brown coloration. The dorsal nectary organ on the 7th abdominal segment and the tentacular organs on the 8th abdominal segment are now distinguishable. The body colour gradually loses the yellow tone and becomes much greener. The growth in this stage brings the caterpillar to a length of about 6mm, and after about 4-5 days in this stage, it moults again.
The 3rd instar caterpillar resembles the 2nd instar caterpillar closely with minor changes observed. The oblique lateral stripes are now more prominent, being more whitish and outlined with darker green than the base green colour. A faint dorsal band, in darker green, run lengthwise. The peripheral rim of the body is yellowish to whitish. Both DNO and TOs are now rather proiminent, with the eversion of the TOs readily observed. This instar takes 4-5 days to complete with the body length reaching about 12mm before the next moult.
The 4th instar caterpillar bear similar markings as the 3rd instar but with greater colour contrast throughout. The lateral white stripes are now broader and flanked with broader dark green stripes. The dark green dorsal band is also broader and more prominent. This final instar lasts about 9-11 days with length reaching 20mm.
An ant attending to an Acacia Blue caterpillar. Note the eversion of the TOs at the 24th second mark.
Towards the end of the 4th instar, the caterpillar ceases eating and its body turns mostly reddish to purplish brown. It wanders around for a pupation site, and in most cases chooses a spot on a leaf surface. At this time, the caterpillar's body shrinks in length and its body has changed to mostly purplish brown with dark green lateral patches. At the pupation site, the caterpillar spins a silk pad and a silk girdle to secure itself and becomes an immobile pre-pupa.
Pupation takes place after 1.5-2 days of the pre-pupal stage. The pale brownish pupa has the typical lycaenid shape, and numerous irregular shaped dark brown to black speckles. Length of the pupa: 10-11mm.
An Acacia Blue caterpillar moults to its pupal stage.
7.5-8 days later, the mature pupa turns dark in the thoracic and wing case areas, with bluish markings apparent in the wing case. The next day the adult butterfly emerges from the pupa
References:
- [C&P4] The Butterflies of The Malay Peninsula, A.S. Corbet and H.M. Pendlebury, 4th Edition, The Malayan Nature Society.
- A Field Guide to the Butterflies of Singapore, Khew S K, Ink on Paper Comm. Pte. Ltd., 2010.
- Butterflies of Thailand, Pisuth EK-Amnuay, 1st Edition, 2006.
