Research proves all stink bugs are potential macadamia nut pests

Reasons for this were that it is difficult to obtain sufficient quantities of stink bugs by field collection alone, and that breeding and maintaining these insects is far from a simple task.

During 2017/18 sufficient quantities of bugs were obtained, so it was possible to do a trial. Five adult individuals of each stink bug species were placed in sleeve cages tied around a bearing macadamia branch of Beaumont. Five cages were used for each replicate (species).

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The early season trial was conducted during October 2017 and nuts were exposed to stink bugs for three consecutive days. At the termination of the trial, immature nuts were harvested and each nut was dissected and microscopically examined to quantify typical feeding punctures on the inside of the husk.

The same trial layout was followed for the late season exposure trial (April 2018). After exposure, nuts were de-husked, dried, cracked individually with a hand cracker and rated for stink bug-induced kernel damage.

As was expected, the coconut bug was able to inflict significant damage during the early season. What was not expected, however, was that the yellow-edged and woolly stink bugs were also responsible for considerable damage.

The grey-brown stink bug had no effect on nut quality both during the early and late season exposure trials. At ± 5,5mm it was assumed that the mouthparts of the yellow-edged bug were too short to damage the kernels of mature nuts, but results contradict this, as severe kernel damage was observed.

In order to prevent damage, the woolly and yellow-edged bugs should also be considered during the weekly scouting sessions, not just the two-spotted and coconut bugs.

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