Determining host plant preferences for the critically endangered Lord Howe Island stick insect (Dryococelus australis) to assist reintroduction

Abstract

The Lord Howe Island Stick Insect (Dryococelus australis) is one of the world's rarest insects. However, the opportunity to reintroduce the species to Lord Howe Island, and commence the path to recovery, may occur within the next five years. Understanding the insect's host plant and habitat preferences on Lord Howe Island is critical to maximising the likelihood of reintroduction success. However, very little ecological information was documented before the species became extinct on the island in the 1930s. Here we examine the Lord Howe Island Stick Insect's preference for potential host plants, a key aspect of habitat suitability. We conducted preference trials using 15 common plant species found on Lord Howe Island. Both nymphs and adults consumed some but not all of these plant species.Nymphs were able to survive on seven of these 15 plants for the duration of the 26-day trials although failed to survive on some of the plants most preferred by adults. Overall, these data reveal that there are numerous plants on Lord Howe Island that the stick insect can consume, though their suitability varies with different developmental stages of the insect. These data are encouraging for any future reintroduction attempts and would greatly aid the selection and monitoring of release sites. one or more large (rodent-proof if necessary) enclosures of potentially suitable forest on the island. This would allow behaviours, including host plant use and preferences, and rates of survival and population growth to be examined in a natural, but contained environment.Finally, we hope that this approach to assessing host plant use and preferences may be of value to other conservation programs that are investigating the reintroduction or introduction of herbivorous invertebrates.

Long‐term captivity is associated with changes to sensory organ morphology in a critically endangered insect

“…This was driven by the TWC type of chemoreceptor which is associated with TA B L E 1 Ordinary least-squares models for the densities of types of antennal sensilla for which population or sex did not explain a significant amount of variation detecting airborne odours and compounds in solution (Slifer, 1966) and is likely the predominant sensilla for the detection of plant volatiles and pheromones. D. australis feeds on a range of food plants found on LHI but clearly prefers a few species (McGrath et al, 2017), whereas M. howeana may be the only food plant on BP and is the most frequently provided in captivity (Honan, 2008;McGrath et al, 2017). Perhaps individuals on LHI relied on plant odours to identify and locate their preferred food plants, while those on BP and in captivity have little or no requirement to exercise a choice.…”

“…The Lord Howe Island, Ball's Pyramid and captive environments differ in the complexity of the sensory environment. Firstly, Lord Howe Island has diverse vegetation with which the LHISI historically interacted, including both food and non‐food plants (Honan, 2008; McGrath et al., 2017), while the LHISI on Ball's Pyramid is known to associate only with the Lord Howe Island Melaleuca Melaleuca howeana . This plant is also one of only a few host (food and shelter) plant species provided to the Melbourne Zoo captive population (Honan, 2008; McGrath et al., 2017), meaning that both the Ball's Pyramid and the captive populations rarely use odours to differentiate among food and non‐food plants.…”

Insect threats and conservation through the lens of global experts

“…Nevertheless, species management may be a tool to be explored further in insect conservation, namely for relatively well‐known species within very limited areas that undergo habitat recovery. For instance, big progress in the Lord Howe Island stick insect's conservation story assures that careful species management could lead to successful reintroduction of a critically endangered insect species within the next few years (McGrath et al., 2017).…”

Conservation Biology: A Walking Stick’s Redux on Lord Howe Island

“…It does face additional obstacles, foremost amongst them is the challenge of eradicating the ship rat (and to a lesser extent the house mouse), no small task when considering the altitudinal range and habitat complexity of LHI [15]. There are also other factors to consider, such as cascading impacts [16] and the host plant preferences of the stick insect that need to be met [17]. Obstacles aside, a successful re-establishment of the LHI stick insect will serve as a flagship for invertebrate conservation on a global scale.…”

“…Obstacles aside, a successful re-establishment of the LHI stick insect will serve as a flagship for invertebrate conservation on a global scale. It can also provide a window into the extraordinary species diversity of LHI, as well as the phylogenetic diversity of many of its taxa, including the LHI stick insect itself [17]. There are over 1,600 species of invertebrates on an island of 14.55 square kilometres, many of which are known from no other place, including species new to science [18].…”