What are Cycad Blue Butterfly and How to Control in Your Garden

Lepidoptera: Lycaenidae

The Cycad Blue Butterfly (Theclinesthes onycha) is endemic to Australia and it is found on the east coast from Cape York to southern New South Wales. There are two subspecies: Theclinesthes onycha capricornia which occurs from Cape York down to Mackay in Queensland, and Theclinesthes onycha onchya which occurs from Blackdown Tableland National Park, Queensland, south to around Central Tilba, New South Wales.

Like many butterflies in the family Lycaenidae their larvae are often attended by ants. The ants provide protection for the larvae in exchange for the sweet fluid exuded by the butterfly larvae. The Cycad Blue is the only butterfly in Australia whose larvae feed on cycads or any other Gymnosperm (cone-producing plants including conifers, ginkgos and cycads).

Best Treatment for Cycad Blue Butterfly

The best way to protect your cycads is to prevent Cycad Blue butterflies laying eggs in the growing tips of your plants. Netting is the best way to achieve that. Prevention is always better than cure. As well as trying netting, there are a couple of other things that you can do to prevent damage from Cycad Blue larvae (see How to Prevent Cycad Blue Butterflies Appearing).

The secret to controlling any pest is to keep an eye on your plants so that you can spot pest incursions early. For example, you could keep an eye out (see Monitor) while you are watering your garden – check for butterflies flying around your cycads, and check if any new growth is developing.

If you haven’t netted your plants, you could check new fronds for larvae - for this to work you will need to know what Cycad Blue larvae look like (see Description).

Regular monitoring of your cycads will ensure that a major infestation of Cycad Blue larvae doesn’t occur ‘overnight’. Managing any pest is much easier if you can catch an infestation in its early stages.

If you notice the larvae, spray with Yates Success Ultra. Repeat at 7-14-day intervals and concentrate on spraying the new flush growth – they love to feed on the soft new leaves. Ideally, treatment is applied when the larvae are small, but it can still be used to control mature larvae, especially if they are still causing damage.

What are Cycad Blue Butterfly
and How to Get Rid of Them

The Cycad Blue is an attractive native butterfly normally found fluttering around the understorey of east coast forests. It has become a horticultural pest due to its larvae damaging cycads in cultivation.

Description

There are two subspecies of this butterfly, and each subspecies has a summer and winter form, so there is considerable variation in adult appearance.

The Cycad Blue is a small to medium sized butterfly with a wingspan of about 24 mm. The upper side of the fore wings are lilac-blue with brown edging. The upper side of the hind wings are similar except the brown edging may include a pattern of white ringed black spots.

The underside of both pairs of wings is a variable pattern of mottled brown, dull grey and dull white. There are two prominent black spots, sometimes called ‘eyespots’, near the base of the wings that are edged in orange. The hindwings also have a distinct white tipped ‘tail’.

Cycad Blue butterfly eggs are disc shaped about 1 mm in diameter, and pale green or white.

Cycad Blue larvae are squat caterpillars which are about 2 mm long when they hatch from eggs but grow to about 12 mm long. They are dark green to brownish green in colour with a brown head.

Cycad Blue pupae are about 10 mm long and are pale brown blotched with dark brown.

Life Cycle

Cycad Blue butterflies develop through a life cycle of complete metamorphosis – egg, larva, pupa, adult. Female butterflies lay their eggs singly on the soft fronds of flush growth. Larvae usually feed at night, or during late afternoon, on young shoots and stems. Larvae usually spend the day at the base of fronds or on the underside of fronds.

Pupation occurs at the base of older fronds and butterflies emerge about a week later. There are several successive generations per year, and adult butterflies may occur during any month of the year.

What Plants are Impacted by
Cycad Blue Butterfly

Cycads including:

Sago palm (Cycas revoluta), Cycas circulus, Cycas media, Cycas ophiolitica, Cycas megacarpa
Burrawang cycad (Macrozamia communis), Macrozamia spiralis, Macrozamia pauliguilielmi, Macrozamia miquelii
Cycas species are damaged by the Cycad Blue subspecies capricornia, and Macrozamia species are damaged by the subspecies onycha.
Cycad Blue Butterfly is not known to damage other cycads such as cardboard cycad (Zamia furfuraceae) and other Zamia spp., Bowenia spp., Encephalartos spp. and Ceratozamia spp.

Symptoms of Cycad Blue Butterfly

Chewed shoots and stems of flush growth. Cycad Blue larvae do about 90% of the damage when they have reached full size – about 12 mm long. They are much less damaging when they are smaller (and younger).
Cycad Blue larvae only feed on young growth but as the fronds grow and open they develop a scorched and ragged appearance.
Severe infestations may result in the loss of all new growth and the heart of the plant may be completely eaten out.

How to Prevent Cycad Blue Butterfly Appearing

Monitor

Watch for butterflies fluttering around the apex of cycads or laying eggs on soft young growth.
Watch for ants climbing into the cycads.

Prevent

Cycad Blue larvae only damage new growth. Cover flush growth with butterfly netting until leaves have hardened. The net must have a mesh of 5mm or less to prevent wildlife becoming entangled. Deploy the net above the flush growth, not against it – otherwise butterflies may attempt to lay eggs through the mesh.
Larvae are usually attended by various species of ants. Control ants and let predators and parasites do their work.
Look for larvae at the base of plants and pick them off. Try to do this before they reach full size.
Look for eggs on soft young fronds and squash them.
Grow less susceptible cycads such as the cardboard cycad (Zamia furfuraceae), other Zamia , Bowenia spp., Encephalartos spp. and Ceratozamia spp.

Natural enemies

Parasitic wasps attack larvae.
General predators of caterpillars including assassin bugs, mantids, predatory beetles, spiders and wasps may feed on larvae.