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Ficus sandpaper cabbage beetle (238)

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Photo 1. Close-up of damage done by the fig-leaf beetle, Poneridia, on sandpaper cabbage.

Photo 2. Egg mass of fig-leaf beetle, Poneridia, on sandpaper cabbage. Note the conical eggs taper to a fine point.

Photo 3. The grubs or larvae of the fig-leaf beetle, Poneridia, characteristically line up near the edge of the leaf and move across the leaf surface together.

Photo 4. The larvae of the fig-leaf beetle, Poneridia, become more scattered when the leaf surface has been eaten and they seek fresh food.

Photo 5. Adult fig-leaf beetle, Ponderidia species. The male is showing 'male-gating', i.e., preventing his partner from mating with competitors.

Photo 6. Gray patches on leaves of Ficus sandpaper cabbage caused by fig-leaf beetle, Poneridia, stripping the leaf surface.

Common Name

Fig-leaf beetles

Scientific Name

The genus is Poneridia (family Chrysomelidae); there are several similar species, but not all the species of Poneridia feed on figs.

Distribution

Narrow. Fig-leaf beetles are recorded from Australia, Indonesia (South Maluku), Papua New Guinea, and Solomon Islands.

Hosts

Fig-leaf beetles feed only on Ficus (including the commercial fig). In Papua New Guinea, the fig-leaf beetle is a pest of sandpaper cabbages, the young leaves of which are eaten as a vegetable.

Symptoms & Life Cycle

The most obvious damage is done by the larvae which strip the surfaces of leaves, they skeletonise them (Photo 1). The adults chew the edges of the leaves, which produces relatively less damage compared to that caused by the larvae.

Eggs are salomon pink, conical, tapering to a point, laid in roughly circular masses, 10-12 mm diameter, on the under side of leaves (Photo 2). The masses contain approximately 100 eggs. They hatch giving rise to grubs with legs (larvae) that are at first yellow and then black. Often they line up along the edge of the leaf to feed (Photo 3). The larvae have prominent hairs, and grow to about 12 mm. When mature, they fall to the ground, and pupate at the base of the tree.

The adults of all species of fig-leaf beetles are mostly brown with partly reddish heads and legs, and dense short hairs on the wing cases or "elytra" (Photo 5).

Impact

The damage done by the larvae to the small shrubby trees can be extensive (Photos 6). The damage usually occurs on the older leaves, leaving the younger ones to be plucked for eating. Destruction of the older leaves is likely to slow shoot production, but by how much is unknown as there has been no research on this pest.

Detection & Inspection

Look for silver-grey leaf patches where the leaf surface has been removed. Look for the black larvae with spines, especially on the upper surface of the leaves.

Management

CULTURAL CONTROL
Ficus sandpaper cabbages are rarely planted; mostly the shoots are collected from plants growing in the wild. This means that control measures are rarely applied against fig-leaf beetles. However, if management of the beetles was required, cultural control measures would be the most appropriate. Of those available, do the following:

• Hand pick the beetles and/or grubs, and destroy them, or squash them on the leaves.
• Cut off the leaves or entire shoots if the beetles and/or the grubs are too numerous for hand picking. Do this carefully, capturing the adult beetles, preventing them from breeding on other shoots.
• Prune the trees to head height so that collecting the insects and/or removing shoots can be done easily.

CHEMICAL CONTROL
This is not recommended as the leaves are mostly collected from plants growing in the wild. If needed, pyrethrum, derris or malathion would be suitable.

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