In record time, the introduced insect responsible for Pandanus dieback, Jamella australiae, spread across the eastern shores of Fraser Island, leaving a wake of destruction.
In less than seven years, the death toll of Pandanus tectorius went from a few hundred plants in 2010 to over 30,000 dead Pandanus across 70 kilometres by 2015. In late 2019, deaths are now approximately 50,000. Jamella has now reached the western shores, where significant populations, particularly in the NW end of the island are also under threat.
In no other location where Jamella australiae invaded had the death toll been so high and the hopper so quick to spread. Why was the death so high on K’gari? For one simple reason, the main predator of the Planthopper (a micro-egg parasitoid wasp) was not released due to concern “of another biocontrol gone wrong (e.g. the cane toad) (FIDO MOONBI 130). Other areas where this micro wasp was promptly released demonstrate an average spread of Jamella at 1 km per year. Fraser Island displayed ten times that rate of spread!
The micro wasp (Aphanomerus nr. pusillus) relies entirely on Jamella australiae for survival and will prevent up to 95% of Jamella from even hatching. Without the micro wasp present, Jamella australiae numbers soared and moved across the eastern shores of the Island like a plague of locusts, feeding exclusively on Pandanus, and reaching numbers in excess of 1 million on single individual mature trees! As each Pandanus died, adult Jamella would then simply fly to the next Pandanus and repeat, their numbers growing exponentially along with secondary dieback contributing insects as the death toll rose ever higher.
So, what’s the problem? They are just plants! Why and how would dead Pandanus harm K’gari’s wildlife? Especially dingos?
Pandanus tectorius have a unique morphology, function, and life cycle traits, unlike any plant – not a palm, cycad, or fern, not like, nor related to any other trees apart from those in the Pandanaceae family. They have a long history in Australia, evolving on ancient Gondwana, in an area now known as Queensland, from ancestors long lost, and long before humankind. Traditional custodians along eastern Australia, (and throughout the Pacific Ocean, Asia through to West Africa) have long farmed Pandanus, as they provide an abundant food source, fibres for weaving, medicinal and ceremonial properties, and shelter from sun, rain, and wind, traditionally used as a living hut. As a result, K’gari had an abundance of Pandanus, more highly concentrated than anywhere in Coastal Eastern Australia, with large populations and pure stands, many greater than a hectare, kilometres from the high tide mark in the high hind dunes! I firmly believe these large hind dune populations were planted by Butchulla, Ngulungbara and Dulingbara ancestors to provide shelter capable of supporting entire tribes, mainly through cyclone and prolonged wet period events (picture living community centres).
Making a link to dingoes
Well, due to the long history on this continent, a plethora of insects and other invertebrates have evolved to be dependent on Pandanus (many entirely host-specific). These, in turn, support a plethora of predators including spiders, geckoes, skinks, birds, rodents, frogs, snakes, bats, possums, etc. The loss of habitat resulting from the death of 50,000 Pandanus has dramatically reduced the abundance of biodiverse lifeforms relying directly and indirectly on Pandanus.
Let’s consider just one group that Pandanus support, rodents. Native rats (Rattus spp.), and Melomys species are very common in Pandanus in healthy coastal ecosystems (especially on K’gari) due to the safe, protected habitat Pandanus provide, having dense spikey leaves and fortress-like prop roots. The edible roots, fruit, and abundance of long-lived seeds occurring under female trees provide an abundant and permanent food source for our furry friends. These rodents, perpetually overflowing from Pandanus into the surrounding vegetation, combined with the goannas, carpet pythons and other snakes which feed on them, all provide a substantial part of a dingo’s diet. Dingo scat research suggests that rodents occurred in between 8.9 and 39 % of scat samples (Behrendorff et al., 2016).
50,000 Pandanus would have supported an estimated 10,000 and 20,000 rodents. Ignoring all other wildlife, if K’gari dingos ate one rodent per day, the rodents produced by those 50,000 dead Pandanus would potentially support somewhere between 54 and 110 dingoes. K’gari’s dingo population is estimated to fluctuate between 100 and 200. Although dingoes consume a broad diet, there is no doubt that the unprecedented loss of K’gari’s Pandanus populations will have impacted on their available food source.
No other plant occurring in SEQ’s Coastal Ecosystems provides food and habitat for such an abundance of invertebrates and wildlife, a food chain that extends out to the surrounding vegetation. On K’gari, the animal at the top of that food chain is the Dingo.
Dieback management into the future
The wasps captive-reared and released (FINIA 2015) at 37 sites across the eastern shores of K’gari as a volunteer with QPWS assistance in 2015-2016, were impressively effective to halt the rapid and widespread mortality occurring at the time. Yet, in common with other areas where Jamella australiae has naturalised and have not managed, dieback continues, albeit slower, a decline of Pandanus populations continues.
One-off wasp releases are not the end of Pandanus dieback prevention methods, but a crucial beginning. For ecological, geographical and climatic reasons, localised extinction of the micro wasp occurs. When this happens, Jamella australiae rapidly increase, causing ongoing cases of dieback. Twice yearly monitoring of Pandanus populations and dieback preventative wasp translocations where Jamella australiae has naturalised is the least that should be done to protect these socially, culturally, and environmentally plants; and the abundance of wildlife they support!
With adequately informed ecological management strategies, Pandanus dieback can be prevented. Many stakeholders across SEQ and northern NSW faced with this issue have inaccurately believed chemical pesticide is the only option, but this is not the case. Broad-scale chemical treatment (‘treat them all approach’) has been applied across many parts of SEQ, resulting in dramatic reductions of beneficial predators and non-target herbivorous invertebrates.
During surveys across SEQ, I have encountered many insects which rely exclusively on Pandanus. In five years of active field research and dieback mitigation work across SEQ, dozens of host-specific relationships and dieback-contributing secondary insects have documented for the first time. Well over a dozen of them have not even been named. Through my work and field research, I have also confirmed that the chemical pesticide (Imidacloprid) used to control Jamella australiae also kills virtually all insects that feed on Pandanus (except for a few pest species; scale and the long-tailed mealybug and detritus-feeding insects such as cockroaches, millipedes, and silverfish). Treated plants may look healthy, but they are sterile of life for around two years. This has certainly caused localised extinction of multiple host-specific insects in some heavily treated areas in SEQ. The use of pesticide should only be considered a last resort for highly stressed and significant plants that are sure to die.
Existing and developing cases of dieback have consistently been prevented at numerous locations across SEQ, through applied ecologically informed mitigation techniques; understanding plant health, insect and predator lifecycles and interactions, utilising the highly effective parasitoid wasp (Aphanomerus nr. pusillus), and small-scale hands-on leaf strip work (assessing and treating the cause rather than the symptom).
Unfortunately, the promotion of leaf stripping to prevent dieback across SEQ has led to many wasted man hours and the misdirection of limited financial resources. With informed plant health and predator/prey assessments, leaf stripping is effective to prevent dieback; when Jamella and secondary insect numbers are elevated, and growth crowns are damaged and rotting. However, removing too many leaves (over stripping) in such cases will cause the central growing point of crowns to drop off and perish.
Leaf stripping healthy (non-infested) Pandanus removes and adversely affects a range of invertebrate predators (especially arachnids) and the parasitoid wasp, also unnecessarily displacing rodents’ nests, birds’ nests, gecko eggs and other beneficial fauna. The unique morphology and habits of Pandanus and the specific interconnected relationships between Jamella australiae, additional secondary (dieback contributing) insects and predators require a high level of commitment, research and experience to make ecologically sound and effective dieback mitigation decisions.
As a society, we’ve accidentally caused this issue through the transport of Pandanus with Jamella australiae and other insects as stowaways, and I believe it is our ethical and moral obligation to do what we can to mitigate the losses and damage to the biodiversity of our beloved (and legally protected) coastal ecosystems. No other coastal natural resource management issue has or is causing such widespread and devasting losses to biodiversity, and yet, is so under-researched and left unmitigated. Loss to habitat and biodiversity would only be paralleled by fire in the coastal zone, which has taken a significant toll on SEQs’ Pandanus populations and Coastal Vine Thicket and Littoral Rainforest Communities, particularly in the coastal islands of SEQ. A Federal Government recovery plan was released in February 2019 for these communities, yet the fire management principles outlined (fire exclusion), for the most part, are yet to be reflected in on-ground management.
I’m eagerly hoping the growing team of Butchulla Land and Sea Rangers will accept an offer made to share all dieback management information, and look forward to again working alongside QPWS rangers and providing all the management insights and lessons learned in the four years since the first fateful collaborative wasp releases on K’gari.
To follow the Pandanus preservation work being done across SEQ (and beyond) and learn management principles as well as learn about the myriad of life forms relying on Pandanus including a mounting number of undescribed-new to science insects, follow this Facebook Page: Pandanus Dieback Education and Information
Article contributed by Joel Fostin