Influence of Jarrah Leaf Miner on the Growth of Jarrah

SUMMARY

Outbreaks of the leaf miner Perthida glyphopa in the jarrah forest of Western Australia have been occurring over an ever-increasing area since the early 1950s. Approximately 0.4 M ha of forest and 1.0 M ha of partly cleared farm land were infested in 1971. In addition, jarrah in scattered groves on the coastal plain has been infested by the leaf miner for at least 60 years.

Some 23 per cent of trees are resistant to the leaf miner's attack.The effect of infestation on girth increment was determined by comparing the growth of resistant and susceptible trees. Over the four years of measurement (1968–71), the annual losses for girth increment in the susceptible trees were 71, 83, 75 and 64 per cent in the forest, and 47, 41, 46 and 33 per cent at a site on the coastal plain. The magnitude of losses was influenced by the density of the insects.