Tropical Nut Borer
Hypothenemus obscurus
A tiny bark beetle that is one of the most damaging pests of macadamia, boring through the hard shell of the nut to feed inside. Widespread in macadamia orchards, it causes steady losses both before and after harvest by tunneling into the kernel.
🔎 How to spot it
The beetle is minute, about 2 millimeters, cylindrical, and dark brown to black, easy to overlook. The sign is a small, round entry hole bored through the nut shell, often with fine boring dust, and tunneling and feeding damage inside the kernel. Fallen and mummified nuts left on the ground are where the beetle builds up.
🥀 Damage it causes
Beetles bore through the shell and feed in the kernel, ruining the nut and opening it to mold and rot, and the damage continues on nuts held in storage. It is among the most consistent and important macadamia pests, found in most orchards, and unmanaged it causes substantial pre- and post-harvest loss.
🛡️ Prevent it
Orchard sanitation is the core defense: harvest promptly and frequently and remove the old, fallen, and mummified nuts on the ground and in the tree where the beetle breeds, since reducing this carryover starves the next generation. Keep harvested nuts cool and dry and process them quickly to limit storage damage.
🧯 If it is already here
Insecticides give poor control because the beetle spends its life protected inside the nut, so management leans on sanitation and timely harvest rather than spraying. Trap-based monitoring using scent and visual lures is used to track activity and time harvests, and stripping and destroying residual nuts each season is the most reliable way to keep numbers down.
💡 Good to know
A round shot-hole through the shell with boring dust is the tell-tale sign. Because sprays cannot reach the beetle inside the nut, frequent harvest and removing leftover nuts are far and away the most effective controls.
For educational and informational purposes only. Pest control advice is general guidance drawn from university cooperative extension sources; always identify a pest positively and read and follow the label on any product before use, especially around food crops, children, and pets.