19 July 2014

Life History of the Cycad Blue

Life History of the Cycad Blue (Chilades pandava pandava)


Butterfly Biodata:
Genus: Chilades Moore, 1881
Species: pandava Horsfield, 1829
Subspecies: pandava Horsfield, 1829
Wingspan of Adult Butterfly: 22-26mm
Caterpillar Local Host Plants: Cycas revoluta (Cycadaceae, common name: Sago Palm), Cycas rumphii (Cycadaceae).





Physical Description of Adult Butterfly:
On the upperside, the male is blue with thin black borders on both wings and it has a black tornal spot on the hindwing. The female is in paler blue with broad borders on the forewing and it has a series of submarginal spots on the hindwing, of which the spot in space 2 is crowned in orange. On the underside, both sexes are pale greyish brown. Both wings have the usual submarginal, marginal and post-discal series of spots and cell-end bars flanked with white. In the hindwing, there is a black spot in the cell, two black spots in space 7, another one just below vein 1a and orange-crowned tornal spots in spaces 1b and 2. There is a white-tipped filamentous tail at vein 2 in the hindwing.




Field Observations:
Cycad Blue is common in Singapore. The adults are usually observed flying in the vicinity of its host plant, the ornamental Sago Palm which can be found in many gardens in commercial, recreational and private residential areas. They are viewed as a pest by gardeners as their presence usually leaves the prized ornamental plants without new growth. The adults visits flowers for nectar and have the habit of sunbathing with open wings in sunny condition.






Early Stages:
Globally,  a fair number of Cycas spp. have been recorded as larval hosts for the Cycad Blue in many countries and regions. In Singapore, two Cycas spp., namely, C. revoluta and C. rumphii have  thus far been identified as local host plants. The caterpillars of the Cycad Blue feed on the immature shoots and young (and still fleshy) leaves of the host plant.

Local host plant: Cycas revoluta.

Young shoots of Cycas revoluta.

A mating pair of the Cycad Blue.

The eggs are laid on emerging young shoots of the host plant when they are still covered in brownish hair or when the green fleshy leaves are still at the stage of being unfurled. Repeated oviposition visits by several females could result in a single shoot being adorned with many eggs.

A Cycad Blue laying an egg on a young shoot of Cycas revoluta.

A Cycad Blue laying eggs on young shoots of Cycas revoluta.

Eggs laid on young shoots, with black arrows indicating where they are present.

Each egg is about 0.45-0.5mm in diameter, pale greenish and 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 Cycad Blue.

It takes about 2 days for the egg to hatch. The newly hatched does not consume the rest of the egg shell after its emergence. It has a pale yellowish body with a length of about 0.9-1mm. The body also features long setae dorso-laterally and along the body fringe. The head capsule is black.

The empty egg shell after the emergence of the caterpillar.

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

The young caterpillar feeds by nibblying away a layer of the leaf lamina. After about 1.5-2 days of growth in the first instar, and reaching a length of about 1.8-1.9mm, the caterpillar moults to the next instar.

Two views of a 1st instar caterpillar, length: 1.5mm.

Two views of a late 1st instar caterpillar, dormant prior to its moult, length: 1.9mm.

In the 2nd instar, besides the moderately long setae which occur dorso-laterally and along body fringe, there are short and fine setae (emanating from dark tubercles) covering the body surface.  The caterpillar could appear in two colour forms: yellow and red. In the yellow form, the caterpillar is yellowish with a strong green undertone, and whitish, narrow, intermittent bands occur dorso-laterally and laterally. In the red form, the caterpillar is reddish brown instead. The 2nd instar caterpillar reaches a length of about 3.2-3.5mm, and after about 1 day in this stage, it moults again.

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

Both colour forms of the 2nd instar caterpillar observed in the field, being attended by ants.

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 proportionately shorter setae on its body. The caterpillar could appear in a yellow or red form, and an intermediate form (essentially yellow form with reddish brown bands). 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 1 day to complete with the body length reaching about 7-7.5mm.

Two views of a 3rd instar caterpillar, early in this stage, yellow form, length: 5mm.

Two views of a 3rd instar caterpillar, yellow form, length: 7mm.

Two views of a late 3rd instar caterpillar, dormant prior to its moult, mixed form, length: 7mm.

A 4th instar caterpillar (in upper half of picture) and a 3rd instar caterpillar of the Cycad Blue found a new (and damaged) leaf of the Sago Palm.

The 4th instar caterpillar has a more distinctive appearance, featuring a dense coat of short whitish setae all over the body surface. Again the same three colour forms observed in the earlier instar are present. The caterpillar can either feed by grazing the leaf surface or devouring the lamina along the leaf edge.

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

Two views of a 4th instar caterpillar, yellow form, length: 12mm.

Two views of a 4th instar caterpillar, yellow form with strong green tone, length: 12.5mm.

Two views of a 4th instar caterpillar, mixed form, length: 12.9mm.

4th instar caterpillars found in the field, attended by ants.

After about 2 days of feeding and reaching a length of about 12-13mm, the caterpillar stops food intake and seeks out a pupation site. During this time, its body gradually shortened. Typically the caterpillar chooses a spot in gaps or cavities present between dried leaves in leaf litter 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, green form.

Two views of a pre-pupa, red form.

After about 1 day as a pre-pupa, pupation takes place. Depending on the colour form of the final instar caterpiller, the pupa can be yellowish green almost entirely, or yellowish to dark reddish brown with numerous black speckles. The pupa has a typical lycaenid shape, and is secured with a silk girdle and cremastral attachment. Pupal length: 9.5-10.5mm.

Two views of a pupa of the Cycad Blue.

Two views of a pupa of the Cycad Blue.

Two views of a pupa of the Cycad Blue.

Four to five days later, the pupa turns black, 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 Cycad Blue.

A newly eclosed Cycad Blue resting on its pupal case.

References:
  • [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 James Chia, Ellen Tan, Bobby Mun, Anthony Wong, Mark Wong, Federick Ho, Sunny Chir and Horace Tan

2 comments:

Donald Kempf said...

Every web site I read, it focuses on controling the blue cycad butterfly during the caterpillar stage. Yours is the only site with some cocoon pics. This life cycle takes how long? Can we upset this life cycle at any other stage?
Normally by the time I either notice the butterfly or the new cycad growth, the damage has already been done and any spray is just a waste.
I would like to attack the grub at another life stage. We used cheap home brand fly spray on the butterfly. It worked but the catapiller attack still came.

Horace said...

In our hot climate, the larval stage only lasts about 7 days or so.
I am sorry that the Cycad Blue is causing problems to your cycad plants. May be you could try googling for possible solutions to mitigate the infestation problem.