The fig-tree skeletonizer moth or fig leaf roller (Choreutis nemorana) is an insect belonging to the order Lepidoptera, family Choreutidae. It is among the most common fig tree parasites, being widespread in all Italian regions and, generally, in the entire Mediterranean area. This insect lives solely at the expense of the fig tree, primarily attacking the leaves. Fortunately, it does not cause severe damage, unlike other pests (such as the black fig weevil), but its presence must be carefully monitored. Moreover, if infestation outbreaks are high, intervention with some biological products is necessary.
Let’s explore how to recognize the fig-tree skeletonizer moth, the damage it causes to the trees, and the biological defense techniques.
Description of the Adult Fig-Tree Skeletonizer Moth
The adult Choreutis nemorana is a small butterfly with a wingspan of 15 mm. The forewings are chestnut-red, recognizable for two wide transversal bands of ashy color, with the outer band being wider. The hindwings are brown with yellow spots.
The fig-tree skeletonizer moth egg is roundish but slightly convex. The color, once laid on the leaves, is straw yellow.
At full maturity, these larvae measure about 12 mm in length. They are greenish-yellow with lighter longitudinal lines and have black piliferous tubercles. The head is light yellow. They closely resemble the cabbage worm.
The moth’s chrysalises can be found enclosed in fusiform sericeous cocoons, white in color, built on the leaves. They measure about 7-8 mm and are light brown.
Damage Caused by Fig leaf roller to Fig Trees
The damage to fig trees caused by the fig-tree skeletonizer moth is due to the larvae, which develop by eroding the leaves. Thanks to the protection of dense sericeous threads, they erode the epidermis of the upper leaf surface, sparing the lower surface and veins. The damaged parts tend to dry out quickly, making the leaf appear rather jagged. In cases of severe infestation, immature fruits can also be attacked. The parasite causes deep erosions on the fruit, although not extensive. Fruits affected by the larvae do not mature properly and are unusable.
Biological Cycle of the Fig-Tree Skeletonizer Moth
The Choreutis nemorana completes two generations per year on fig trees. Hibernation usually occurs in the chrysalis stage, on fig leaves fallen near the tree. New adults appear in spring, between April and May, and begin mating activity. A female fig-tree skeletonizer moth can lay between 50 and 60 eggs, which are deposited singly on the upper leaf surface. The egg incubation period lasts 6-9 days. The larvae live on the upper leaf surface, within dense sericeous threads. They only come out with their heads to feed on the leaves. When they molt, the larvae leave their sericeous cocoon and build a new one. Thus, these small white bumps will be visible on the vegetation.
When fully mature, the fig-tree skeletonizer moth larvae use the folded leaf edge to weave another elongated sericeous cocoon to pupate. The new adult emerges after about 10 days, initiating the second generation. The new adults usually fly between late June and early August. The second generation of larvae is practically present on the leaves until the fall.
How to Prevent Fig-Tree Skeletonizer Moth Infestation
As mentioned, the fig-tree skeletonizer moth spends the winter in the chrysalis stage, inside sericeous cocoons formed on fallen fig leaves. Thus, by removing the vegetation residues in the fall, the presence of the insect in the following year can be avoided. Usually, this cleaning operation under the tree is not carried out, leaving the organic matter to decompose. However, if there has been a fig-tree skeletonizer moth attack in a season, it is advisable to perform this cleaning.
How to Eliminate Fig-Tree Skeletonizer Moth
Interventions (with products allowed in organic farming) are justified only in cases of major infestations when the larvae start damaging the fruits. The most effective product against the larvae of this insect is Bacillus thuringiensis var. kurstaki. This product works through ingestion and is easily available for purchase without the need for a phytosanitary product license. To ensure some effectiveness in the biological treatment, abundant wetting of the upper leaf surface, where the sericeous cocoons protecting the larvae are located, is necessary. It is better to carry out the wetting in the evening hours to have a prolonged effect.