The black twig borer (Xylosandrus compactus) is a tiny beetle that creates a small entry hole and then a tunnel within the twigs of Acacia koa and many other woody cultivated and native plants in Hawaii. The beetle lays eggs in the tunnel and introduces a fungus (the ambrosia fungus) upon which the hatching larvae feed. The damage to the infested twig usually results in twig death within 7-10 days. The twigs dry up and the leaves shrivel and turn brown. The larvae become adults and fly to nearby twigs to repeat the process. The twig borer is almost impossible to control. Damage can be reduced on small koa trees in landscape settings by clipping off infested twigs and destroying them and the beetles and larvae inside.

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