Cassia Seed-Borer Moths

Cassia tomentella

Cassia tomentella opened seed pod

Photos of the moth were sent to moth enthusiasts but none were able to assign a genus or species to the moth. This is not surprising as Australia has between 20,000 and 30,000 moth species. A large proportion of these have not been described. The closest identification that could be assigned to the moth was to the Family Pyralidae, Subfamily Phycitinae.

Family Pyralidae is one of the largest and megadiverse families of moths. Adults adopt many postures, biologies, and behaviours. They are distinguished from most other moths by having a scaled base to the proboscis, abdominal hearing organs, and prominent labial palps which protrude forward in front of the head.

The Subfamily Phycitinae contains moths that are typically concealed feeders, living in silken webs made up of leaf fragments. Many bore into trunks, stems, fruit, seed pods, and galls. The most famous Phycitinae is the cactus moth Cactoblastis cactorum which is responsible for the biological control of Prickly Pear in southern Queensland. It was introduced in the 1920s and is still controlling the pear. Its larvae feed in the fleshy green areoles reducing them to a pulp. Another moth in this Subfamily is Etiella behrii. It is widespread in Australia and also overseas. It is a pest of legumes, the larvae boring into the pods and seeds. The moth attacks peanuts, soybeans, peas, lupins and lucerne.

Cassia tomentella damaged seed

Cassia borer-moth

Other Cassia seed-borer moths

There may be more than one species of moth whose larvae bore into the green seed pods of Cassias. Another one has come to light on 26 January 2020 when Glenn Leiper observed and photographed another moth which emerged from a pupal case attached to a Cassia tomentella seedpod.

This moth belongs to another moth family (Tortricidae), and normally feeds in the green nuts of several Macadamia species. I have identified the moth as Cryptophlebia ombrodelta (Family Tortricidae).

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Cryptophlebia ombrodelta

Cassia seed-borer moth life cycle

The life cycle has not been fully described but ties in nicely with the life cycle of the Cassia trees. Adult moths are around from mid October to mid November. At this time the adult female must lay eggs on the seed pods. At this time, the pods would be small and soft as the tree flowers from late October to early November. Moth larvae would hatch and start feeding on the developing seeds, etc. The larvae grow to about 8mm to 10 mm long. Just before pupation I would assume that the larvae chew a hole around 2.5mm in diameter from inside the pod to the outside, and then pupate next to the hole. When the moth emerges I assume that the pupa forces its way halfway through the hole by moving its abdomen backward and forward. The moth then emerges and flies off.

Acknowledgment
Peter Hendry: Identifying the Cassia borer-moth

Cassia borer-moth pupae

Cassia borer-moth larva