A project undertaken at The University of Sydney, and supervised by Dr Nathan Lo.
The critically endangered Lord Howe Island ‘woodroach’ Panesthia lata was first described in the late 1800s, but thought to have gone extinct following the arrival of rats in 1918. It was later found on the nearby Blackburn and Roach Islands, as well as Balls Pyramid, but its biology remained poorly understood.
An individual in the re-discovered P. lata population and is credited to Justin Gilligan.
In this project we sought to better understand the ecology and genetics of P. lata, to assist with its conservation. During the initial stages of the project we searched for P. lata in the northern end of LHI, and to our surprise found it was still present under the rocks beneath one large Banyan tree. This was the first time P. lata had been seen on the main island in around 80 years. We undertook genetic analyses of P. lata from each of the islands on which it has been found, and also compared it to Australian mainland relatives. We estimated that the ancestors of P. lata arrived to LHI via rafting from wood-feeding cockroaches present in coastal south-east Queensland ~2 million years ago. The ancestors of P. lata on Balls Pyramid were estimated to have diverged from those on LHI, Blackburn, and Roach Island ~200,000 thousand – 1 million years ago, while the latter populations appear to have interbred until relatively recently (~17-93 thousand years ago), assisted by sea-level drops during glacial periods. Each of these populations showed relatively high levels of inbreeding, in excess of levels that in other species lead to reductions in fitness and survivorship. The potential for breeding between different populations should therefore be considered.
Our ecological studies showed that P. lata typically nests under rocks beneath Banyan trees, emerging at night to feed on Banyan leaves, with the exception of Roach Island, where previous studies have shown that it nests under leafy flat sedge. It is likely to play an important role in recycling dead plant matter, enriching soil, and possibly acting as a prey source for birds or other animals. Comparative behavioural studies showed that P. lata’s males are far less aggressive than close relatives in mainland Australia, and that, unlike the latter, P. lata changes its shelters frequently. This, in combination with its relatively large size and loss of wings, fits with P. lata have evolved a typical ‘island phenotype’. Since the eradication of rodents in 2019, the LHI woodhen has increased dramatically in numbers.
Our studies show that P. lata has survived this increase on LHI, despite it likely being a prey target for the woodhen, thanks to its highly reclusive behaviour. This same behaviour, and its strict habitat requirements means it is not a potential nuisance for those living on the island. Our rearing studies showed that P. lata survives readily in captivity, and can reproduce. We hope that our findings will help to ensure P. lata’s continued presence on LHI in the long term. (Photo credit: Justin Gilligan)