20 October 2012

Life History of the Yellow Vein Lancer

Life History of the Yellow Vein Lancer (Pyroneura latoia latoia)

Butterfly Biodata:
Genus: Pyroneura Eliot, 1978
Species: latoia, Hewitson, 1868

Sub-species: latoia, Hewitson, 1868
Wingspan of Adult Butterfly: 34-36mm
Caterpillar Local Host Plant: Oncosperma horridum (Arecaceae, common name: Mountain Nibung Palm).

Physical Description of Adult Butterfly:
Above, both sexes are dark brown with the forewing having a number of hyaline spots: two small sub-apical spots in spaces 6 and 7; four decreasing-size pale yellow spots in spaces 2-5; and two elongated cell spots with lower one larger and closer to the wing base There is a yellow streak running from wing base to the costal margin, and a broader one in space 1b. In the hindwing, there is a post -discal series of hyaline spots in spaces 2-5. A streak runs from this post-discal band to the cell-base and another runs to the base of space 1a. Underneath, the wings are marked in spots as per the upperside and in a brown base colour. The veins are marked broadly in yellow with opalescent spots and streaks between them. The cilia are orange in both wings. The antennae are coloured yellow in both the shaft and apiculus in the male, and only the apiculus in the female.

Field Observations of Butterfly Behaviour:
This species occurs mainly in the nature reserves where it is relatively common. Adults are typically found taking nectar from the inflorescence of the forest plant Leea indica. It is not uncommon to observe several individuals on the same inflorescence. The adults are fast flyers and prefer to perch on the upperside of a leaf to rest.

Early Stages:

Local host plant: A partial view of a leaf of Oncosperma horridum.

Local host plant: Oncosperma horridum.

The local host plant, Oncosperma horridum, is a tall clustering palm with pinnate leaves, and with its stem covered in black and downward pointing spines. This palm can be found growing in the Central Catchment Reserve in relative abundance at certain localities. The caterpillars of the Yellow Vein Lancer feed on leaves of this plant, and live in shelters made by joining edges of leaf fragments together with silk threads.

A mother Yellow Vein Lancer laying an egg on the upperside of a leaflet of the host plant.

The eggs are laid singly on the upperside of a leaflet of the host plant. Each dome-shaped egg has a thickened whitish rim surrounding a circular polar region which houses the micropylar. A number (18 and 19 in the two eggs observed) of radial whitish ridges run from the rim to the base. The base diameter is about 1.5-1.6mm. When freshly laid, the egg is pinky red to salmon red. The colour changes to pale yellow or greyish white as the egg matures over the new few days.

Two views of an egg of the Yellow Vein Lancer.

A mature egg with the young caterpillar already nibbled away the polar part of the egg shell.

It takes about 4 days for the egg to hatch. The young caterpillar eats just enough of the shell to emerge, and has a length of about 4mm. Its body is mainly yellowish orange and its head black in colour. There is a black collar on the prothorax. The newly hatched proceeds to consume the rest of its egg shell soon after emergence. With its first meal consumed, it will then build its first leaf shelter by cutting a leaf fragment, folding it over and securing it to the opposing leaf lamina with silk threads.

A sequence of three pictures showing the construction of the first leaf shelter.

Two views of a 1st instar caterpillar, length: 3mm.

The body color changes to pale yellowish green after a few feeding sessions on the leaf. Between feedings, the caterpillar retreats to its shelter for rest and security. The 1st instar takes about 3 days to complete with the body length reaching up to 5.5-6mm.

1st instar caterpillar, late in this stage, dormant prior to its moult, length: 5mm.

The 2nd instar caterpillar is yellowish green in body colour. A touch of reddish orange on its dorsum can be seen in the early part of this instar. A colour change in the head results in it being dark yellowish brown with a broad black band lining its periphery. The black collar on the prothorax seen in the 1st instar is no longer present. This instar lasts about 4 days with the body length reaching about 7.5mm-8mm.

Two views of a 2nd instar caterpillar, early in this stage, length: 4.5mm.

Two views of a 2nd instar caterpillar, late in this stage, length: 7.5mm.

Two views of a 2nd instar caterpillar, dormant prior to its moult.

The 3nd instar caterpillar resembles the 2nd instar caterpillar closely in body markings and coloration. The only visible change is in the lightening of the shade of yellowish brown colouration of the head capsule. This instar lasts about 4 days with the body length reaching about 11-12mm.

Two views of a newly moulted 3nd instar caterpillar, eating its exuvia.

Two views of a 3nd instar caterpillar, later in this stage. length: 9.5mm.

The 4th instar caterpillar is pale yellowish white in body color with a green undertone. The head capsule has a faint black stripe along the front cleavage line. The base colour of the head capsule is paler than in the earlier instar. Two elongated whitish marks, rather faint in this instar, appear in the area between the mouth and the stemmata (eyes) on each side. This instar lasts 4 days with the body length reaching up to about 16-17mm.

A newly moulted 3nd instar caterpillar, eating its exuvia.

Two views of a 4th instar caterpillar, female, length: 17mm.

The 5th (and penultimate) instar caterpillar resembles the 4th instar caterpillar closely with the only change occurring in the head. The black stripe lining the front cleavage line is now broader, and in some specimens, two small black "cheek" marks appear. The two elongated marks lying between the mouth and the stemmata (eyes) on each side, which first appear in the previous instar, are now more prominent. A dorso-lateral white band, faint in appearance, one on each side of the body, runs lengthwise from the prothorax to the anal plate. This instar takes about 4-6 days to complete with the body length reaching up to 24-25mm.

A newly moulted 5th instar caterpillar.

Two views of a 5th instar caterpillar, length: 25mm.

The 6th (and final) instar caterpillar resembles the 5th instar caterpillar closely with the body colour lightened to a pale shade of yellow. In the head capsule, the "cheek" marks become a fixture, and all black markings are now bolder and prominent. Likewise, the two dorso-lateral whitish bands spanning the body length are now more eye-catching. This instar takes about 8-9 days to complete with the body length reaching up to 35-37mm.

A newly moulted 6th instar caterpillar.

A 6th instar caterpillar, length: 31mm.

Towards the end of the 6th instar, the body of the caterpillar shortens and its coloration changes to a very dark shade of yellowish green with a strong purplish undertone. Colour darkening is also seen in the head capsule. Soon it becomes dormant in its leaf shelter and enters the prepupatory phase, during which it secretes a white waxy substance and spins a silk pad and a silk girdle to ready itself for the pupation event.

A 6th instar caterpillar, late in this intar, length: 36mm.

A 6th instar caterpillar, with colour changes taken place, and after cessation of food intake, length: 30.5mm.

A pre-pupa of the Yellow Vein Lancer.

After a pre-pupal period of about 2 days, pupation takes place within the leaf shelter. The pupa secures itself with a (weak) silk girdle and cremastral attachment to transverse silk bands on the substrate. It is dark brown in the anterior end (including the head, thorax and the wing case), and pale yellowish brown in the abdomen. Length of pupae: 20-21mm.

Two views of a pupa of the Yellow Vein Lancer.

On the last day of the pupal period, the pupa becomes mostly dark brown with yellow markings (on the forewing upperside) visible in the wing cases. Finally after a pupal phase of about 9.5-10 days, eclosion takes place with the adult emerging from the pupal case.

Three views of a mature pupa of the Yellow Vein Lancer.

A newly eclosed Yellow Vein Lancer.

  • [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, 1st Edition, 2006.
  • A Field Guide to the Butterflies of SIngapore, Khew S K, Ink on Paper Comm. Pte. Ltd, 2010.
Text by Horace Tan, Photos by C K Chng, Anthony Wong,  Khew SK and Horace Tan

No comments: