By now I’m sure the vast majority of the readers of the FINIA newsletter are aware of the Pandanus dieback occurring in Pandanus populations in South East Queensland and Northern New South Wales, and the severe dieback currently occurring on Fraser Island. Many will also be aware of the leafhopper primarily responsible for the dieback (Jamella australiae).
When a new Jamella outbreak occurs in the absence of the parasitoid wasp (Aphanomerus nr. pusillus), the leafhoppers breed to immensely high infestation levels and spread rapidly. The ensuing fungal pathogens and secondary detrimental insects decrease plant health, resulting in rapid and high mortality rates. Recent observations on the Sunshine Coast and at Agnes Water have uncovered over five non-native secondary insects (garden and agriculture escapees) greatly contributing to plant mortality.
While many predatory insects prey on Jamella adults and nymphs, only the parasitoid wasp has proven effective in mitigating the dieback. The wasp’s high predation rates on the leafhopper’s eggs (often upwards of 80%) lowers leafhopper numbers, greatly reducing the rate at which the outbreak spreads, and prevents the decline in plant health. In this way, the wasps act as prevention, rather than as a cure.
Environmental factors such as prolonged periods of drought or wet weather and cold winter temperatures also influence the predator/prey balance and subsequently the health of Pandanus populations. For Pandanus that are under severe stress, like the many thousands on Fraser Island, direct intervention in the form of leaf stripping or pesticide control is at present the only tested method to assist in their survival. Sadly, it is likely that more Pandanus will succumb until the wasp has been released and become naturalised throughout all parts of Fraser Island.
In recent years, there has been limited state-wide awareness raising, monitoring, research and action carried out to protect these iconic, culturally significant, and arguably the most important coastal ecosystem keystone species. Coastal beaches and coral islands from Gladstone north to Townsville are at risk of new outbreaks. With early detection of new Jamella australiae outbreaks and prompt release of Aphanomerus nr. pusillus, Pandanus dieback can be greatly mitigated.
To manage these outbreaks successfully, collaboration between local councils, parks, indigenous groups and environmental groups is required. Annual monitoring, localised wasp translocation, physical intervention and research into co-contributing insects are also essential. The challenge is coordinating all of these responses across multiple land tenures in an increasingly resource limited environment. Who are you going to call?
Joel Fostin, Student, University of the Sunshine Coast