Life History of the White Four-Line Blue

Life History of the White Four-Line Blue (Nacaduba angusta kerriana)

Butterfly Biodata:
Genus: Nacaduba Moore, 1881
Species: angusta H. Druce, 1873
Subspecies: kerriana Distant, 1886
Wingspan of Adult Butterfly: 30mm
Caterpillar Local Host Plants: Entada spiralis (Fabaceae)


A female White Four-Line Blue perching on a leaf near its host plant in between oviposition visits

Physical Description of Adult Butterfly:
As a member of the pavana group (the Four-Line Blues), the adult does not have a basal pair of lines in the underside forewing cell. Above, the male is purplish blue with a thin black border, about 1mm broad towards the apex; the female has broad black border on the forewing and a light blue ground colour with diffuse greyish markings on both wings. Beneath, both sexes has greyish ground colour with very broad and diffuse whitish-grey stripes. On each hindwing, there is an orange-crowned tornal spot lightly speckled with bluish-green metalic scaling. i Next to the tornal spot, a pair of filamentous white-tipped tails occurs at end of vein 2. Marginal and submarginal spots are black and stand out against the whitish bacground. The prominent rounded black sub-marginal spot in space 6 of the hindwing serves as an important identification key for this species.

A male White Four-Line Blue perching on a branch


A male White Four-Line Blue perching another branch


A sunbathing male White Four-Line Blue showing its upperside

Field Observations of Butterfly Behaviour:
Though included in the early authors' checklists for Singapore, this species has eluded the local butterfly enthusiasts in recent years before its recent re-discovery in the December 2008. Sightings have been confined to a single location where its host plant is thriving at tree top levels. The adult has an erratic flight, and typically makes its appearance in sunny weather. Encounters usually take place in sunlit spots with the adult sunbathing or flitting from perch to perch in the vicinity of its host plant.

Early Stages:
The host plant, Entada spiralis, is a woody climber with bipinnate leaves, usually with 4 pairs in a pinna. Flowers are small and occur in dense racemes. Seed pods are curled with 5-11 very large seeds to each pod. This tree-topping vine can be found in the Central Catchment Nature Reserves as well as in the Southern Ridges. Besides the White Four-Line Blue, locally this plant also plays host to the Large Four-Line Blue (Nacaduba pactolus odon), Common Line Blue (Prosotas nora superdates) and the Common Grass Yellow (Eurema hecabe contubernalis). The early instars of the White Four-Line Blue feed on young leaves of this plant by grazing away the upper layer of lamina. The later instars nibble away the lamina from the leaf edge, as well as the outer layer of young stems.


Host plant : Entada spiralis


Young shoots of Entada spiralis.


A mating pair of White Four-Line Blue


A mother White Four-Line Blue making an oviposition visit to young shoots of E. spiralis.

Eggs are laid on the young shoots of the host plant, typically in spaces between very young and yet to be unfurled leaves. It is not uncommon for a number of eggs to be found on the same shoot, however the eggs occur singly rather than in clusters. Each egg is pale yellowish green, circular and has a depressed micropylar area. The surface is criss-crossed with numerous tightly-spaced lines. Each egg has a diameter of about 0.4mm.


Two eggs of the White Four-Line Blue. Diameter: 0.4mm.

It takes 2-3 days for the egg to hatch. The young caterpillar consumes part of the egg shell to emerge. With a length of about 0.7-0.8mm, it has a pale yellowish body with long setae (hairs) dorsally and sub-spiracularly. The caterpillar assumes the typical woodlouse body shape as it grows. The body color also changes gradually to a brighter shade of yellow. A diamond-shaped pro-thoracic shield and a slight depression on the anal segment can be distinguished easily through contrasting and darker shades of coloration.


1st instar caterpillar, late in this stage. Lengths: 1.5mm (top) and 1.2mm (bottom)

The first instar lasts for 2 days and the body length reaches about 1.5mm before the moult to the 2nd isntar. The long dorsal setae are absent in the 2nd instar caterpillar. The body color is mainly yellow with a greenish undertone. The prothoracic shield is less prominent, being slightly paler than the yellow base color. The 2nd instar also lasts for 2 days and the caterpillar grows to a length of about 3m to 3.5mm.


2nd instar caterpillar, freshly moulted to this instar, length: 1.5mm



2nd instar caterpillar, late in this stage. Lengths: 2.5mm (top) and 3mm (bottom).

The 3rd instar caterpillar is still yellowish green but with an increasing emphasis in green. Faint markings in much paler yellow appear on both sides of the dorsal line. After 2 days in this stage with the body length reaching a maximum about 6-7mm, the next moult takes place to bring the caterpillar to its final instar.


3rd instar caterpillar, Lengths: 3.5mm (top) and 4.5mm (bottom)


3rd instar caterpillar, late in this stage, length: 6mm

The 4th instar caterpillar initially resembles the 3rd instar caterpillar in the day prior to the moult. However as it proceeds to feed and grow in this final instar, the body quickly takes on a much lighter shade of green with the whitish dorsal-lateral shadings more prominent than in the 3rd instar. The prothorcic shield is whitish with a few brown spots, and the dorsal nectary organ and ventacular organs are distinguishable on the posterior segments.


4th instar caterpillar of lengths: 8mm (top) and 11mm (bottom).


Body features of a 4th instar caterpillar. Left: dorsal nectary organ (DNO) and tentacular Organ (TO).
RIght: prothoracic shield.

The 4th instar lasts for 4 days and the body grows up to a length of about 11-12mm. On the last day of this stage, the caterpillar ceases food intake and its body shrinks in length. It wanders around for almost a full day before it comes to rest on a spot among leaves for pupation. The pre-pupatory caterpillar prepares for pupation by spinning silk threads to shape the leaves into a pupation shelter. Within the tight interior of the shelter, the pre-pupatory caterpillar stations itself with silk girdles and the attachment of the cremaster.


Two views of a pre-pupa of the White Four-Line Blue

The next day, after 9-10 days of larval growth, pupation finally takes place. The pupa has the typical lycaenid form, and is 8-9mm in length. It is mostly pale brown and speckled with black spots of various sizes and shapes.


Two views of a fresh pupa of the White Four-Line Blue

Six days later, the pupa becomes darkened in color signaling the imminent emergence of the adult. The markings on the forewing upperside becomes increasing obvious through the upal skin. The next day the adult butterfly emerges from the mature pupa.


Two views of a mature female pupa showing the markings on the forewing upperside in the wing pad.


Two views of a mature male pupa showing the purplish blue forewing upperside in the wing pad


A newly eclosed White Four-Line Blue resting on its pupal case


Another newly eclosed White Four-Line Blue

References:

• The Butterflies of The Malay Peninsula, A.S. Corbet and H.M. Pendlebury, 4th Edition, Malayan Nature Society.
• Butterflies of Thailand, Pisuth Ek-Amnuay, 1st Edition, 2006

Text by Horace Tan, Photos by Sunny Chir and Horace Tan