Cycad killer, qu'est-ce que c'est? Dieback of Macrozamia communis on the south coast of New South Wales

Abstract

The association of an armoured scale insect (a diaspidid) with dieback of a population of a native cycad (Macrozamia communis L.A.S.Johnson) was investigated on the south coast of New South Wales. The diaspidid was found to be undescribed but morphologically similar to oleander scale – here we call it Aspidiotus cf. nerii. It is probably native to Australasia and its current known distribution is within Murramarang National Park (MNP). Aspidiotus cf. nerii has been abundant on symptomatic M. communis at MNP over at least the past decade and has spread to new parts of the park. In population studies of infested and uninfested areas we found that, although both areas had populations with reverse J curves showing dominance of seedlings, mortality of seedlings and caulescent plants was significantly higher in infested sites. Infested areas had been burnt less frequently than uninfested areas. Fire does not appear to eradicate the diaspidid but may reduce its effects enough for plants to recover. We recommend further research into the use of fire as a management tool. Although other factors may be contributing to the severity of the dieback, we suggest there is sufficient evidence for the diaspidid to be regarded as the primary cause of dieback in M. communis in MNP, regardless of its origin. Given the occurrence of similar diaspidids on cultivated plants in botanic gardens, translocation of threatened Macrozamia species using plants grown in nurseries should be undertaken with extreme caution.