The macadamia nut borer (Thaumatotibia batrachopa) is native to Africa and was originally described from the Eastern Cape province in South Africa. Macadamia is the major host of this moth, it has not been linked to any other crop or indigenous host in South Africa. It is a quarantine pest and control procedures have to be carried out to enable export.
Appearance and life cycle of Macadamia nut borer
The eggs are laid singly on young fruit and are flat and oval with a pitted surface. Females can lay between 170 – 300 eggs in their lifetime. The eggs hatch between 7-12 days and the young larvae bore their way into the young fruit. The larvae are cream to grey in colour with dark spots on the body and the head capsule is brown. The pupa is dark brown and (if pupation takes place in the soil) encased in a cocoon of soil particles. There is no cocoon if pupation takes place in the fruit. The moth is small and grey with indistinct darker and paler markings. It has a characteristic saddle-like structure behind the head.
Damage and symptoms
Damage before shell hardening is caused by the larvae which bore into the fruit. In small nuts the entire kernel is eaten, whereas in large fruit, part of the kernel may remain. A larva can consume several small nuts by moving from one fruit to another. This type of damage is small, and trees are able to compensate for damage because of the large volume of flowers and small nuts produced by macadamia trees early in the season. Fruit with hardened shells cannot be penetrated, larvae then feed on the inside of the husk. Damaged nuts are shed by the tree.