22 March 2014

Life History of the Pale Grass Blue

Life History of the Pale Grass Blue (Zizeeria maha serica)

Butterfly Biodata:
Genus: Zizeeria Chapman, 1910
Species: maha Kollar, 1844
Subspecies: serica C. Felder, 1862
Wingspan of Adult Butterfly: 20-25mm
Caterpillar Local Host Plant: Oxalis corniculata (Oxalidaceae, common names: Creeping Wood Sorrel, Yellow Wood Sorrel), Oxalis barrelieri (Oxalidaceae, common names: Barrelier's woodsorrel, lavender sorrel).

Physical Description of Adult Butterfly:
On the upperside, the male is light blue with broad dark blue border on both wings, whilst the female is dark greyish blue. On the underside, both sexes are pale greyish brown. Both wings have a cell-end bar and a spot in the cell, as well as a post-discal band of dark rounded spots. Both wings also have a submarginal series of pronounced spots flanked with v-shaped striae.

Field Observations:
Pale Grass Blue was discovered in Singapore in 2001 and has since become a common species. It was most probably introduced by human agency. The adults can be found in urban parks, grasslands and even in residential compounds and university campuses. The adults have a weak fluttering flight, and are usually spotted in the vicinity of its host plant, Yellow Wood Sorrel, or visiting flowers of various plants for nectar.

Early Stages:
So far, two local host plants, Oxalis corniculata and Oxalis barrelieri, have been recorded as the local host plants for the Pale Grass Blue. The caterpillars of the Pale Grass Blue feed on the leaves and sometimes the young shoots of this host plant.

Local host plant #1:Oxalis corniculata..

Local host plant #2:Oxalis barrelieri..

A mating pair of the Pale Grass Blue.

A mother Pale Grass Blue ovipositing.

The eggs are laid singly on the underside of a leaf of the host plant. Each egg is about 0.4mm in diameter, and whitish with a yellowish green 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.

Two views of an egg of the Pale Grass Blue.

Two views of a 1st instar caterpillar, newly hatched, length: 0.7mm.

It takes about 4 days for the egg to hatch. The newly hatched has a pale yellowish body with a length of about 0.7-0.8mm. The body also features long setae dorso-laterally and along body fringe. The young caterpillar feeds by nibblying away a layer of the leaf lamina, causing thin stripes of whitish marks to appear on the leaf. After about 2-3 days of growth in the first instar, and reaching a length of about 1.8mm, the caterpillar moults to the next instar.

Two views of a 1st instar caterpillar, early in this stage, length: 1mm.

Two views of a 1st instar caterpillar, late in this stage, length: 1.8mm.

Two views of a late 1st instar caterpillar, dormant prior to its moult, length: 1.4mm.

In the 2nd instar, besides the long setae which occur dorso-laterally and along body fringe, there are short and fine setae covering the body surface. The caterpillar is yellowish with a strong green undertone, and whitish, narrow, intermittent bands occur dorsally, dorso-laterally and sub-spiracularly. At this stage, the dorsal nectary organ is present but indistinct. The 2nd instar caterpillar reaches a length of about 2.8mm, and after about 3 days in this stage, it moults again.

Two views of a 2nd instar caterpillar, early in this stage, length: 1.9mm.

Two views of a 2nd instar caterpillar, late in this stage, length: 2.6mm.

Two views of a late 2nd instar caterpillar, dormant prior to its moult, length: 2.4mm.

Compared to the 2nd instar caterpillar, the 3rd instar caterpillar bears a denser coat of proportionately shorter setae on its body. The body could be yellowish green entirely or featuring reddish shading dorsally and along body fringe. 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 4 days to complete with the body length reaching about 5.5-6mm.

Two views of a 3rd instar caterpillar, newly moulted, length: 2.6mm.

Two views of a 3rd instar caterpillar, length: 4.6mm.

Two views of a late 3rd instar caterpillar, dormant prior to its moult, length: 5mm.

The 4th instar caterpillar has a more distinctive appearance, featuring a dense coat of short whitish setae all over the body surface. The body coloration could be entirely green or yellowish green with shadings of red to reddish brown. At this stage, the caterpillar change its feeding habit to devouring the leaf lamina from the edge, rather than "grazing" on the leaf surface.

Two views of a 4th instar caterpillar, early in this stage, length: 7.2mm.

Two views of a 4th instar caterpillar, length: 10mm.

Two views of a 4th instar caterpillar, length: 11.2mm.

After about 4 days of feeding and reaching a length of about 10.5-11.5mm, the caterpillar stops food intake and seeks out a pupation site. During this time, its body gradually shortened. Typically the caterpillar chooses a spot on a stem or the underside of 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 Pale Grass Blue.

After about 1 day as a pre-pupa, pupation takes place. The pupa is predominantly yellowish green to green and some would feature a number of small black spots dorsally and dorso-laterally. It has a typical lycaenid shape. There are whitish fine setae on its body and at the anterior end. Pupal length: 7.5-8mm.

Two views of a pupa of the Pale Grass Blue.

Six days later, the pupa turns black, first in the wing pad and thorax, then progressively in the abdomen. The presence and absence of the bright 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 Pale Grass Blue.

A newly eclosed Pale Grass Blue.

  • 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, Jonathan Soong, Mark Wong, Ben Jin Tan, Federick Ho and Horace Tan


Nick Morgan said...

Fantastic article, as always. The photography is magnificent. I hadn't appreciated how small the newly hatched larva is, but still beautifully captured.

Horace said...

Thanks for the kind words, Nick. :)
It is always a challenge trying to capture still images of newly hatched larvae when they are only about 0.8-1.0mm and very restless.

Unknown said...

very use full article. good work.

Unknown said...

Fantastic article and incredible photos! May I ask if you know whether the dorsal nectar organ is functional in 2nd instars? I am researching the blue butterflies but having a hard time finding anything published that confirms/denies my suspicion that this organ is non-functional at this stage. Thank you!

Rajib said...

A very useful and technically sound article for which I thanks to Horace Tan Sir. I want to ask that every pale grass blue's 4th late instar caterpiller goes to for pupation? I mean instar number is 1 to 4.

Horace said...

Typical number of instars is 4 for Pale Grass Blue. If the caterpillar is healthy and normal in development, it will then go to the pupal stage.