The current rates of species loss and decline are so extraordinary that the Earth is speculated to be on the cusp of entering a sixth mass extinction, with the majority of species lost expected to be insects. Insects make up approximately 70 % of all species on Earth and are proportionally the most under- represented class of animal in conservation biology. An important tool for substantially reducing the risk of extinction for critically threatened species is conservation translocation, which is defined by the International Union for Conservation of Nature as “the intentional movement and release of a living organism where the primary objective is a conservation benefit”. However, there has been limited applications of translocation as a conservation tool for insects, and only 52 % of terrestrial insect translocations are reported as successful at establishing a persistent population. This thesis develops applied conservation management strategies to improve translocation success for insects using New Zealand’s Nationally Endangered robust grasshopper, Brachaspis robustus Bigelow (Orthoptera: Acrididae), as a case study.

Brachaspis robustus is a large bodied, flightless, highly visually cryptic and non-stridulating grasshopper. It is a braided river specialist endemic to the Mackenzie Basin, an inter-montane dryland region in the centre of New Zealand’s South Island. Currently all wild populations of B. robustus that are monitored by the New Zealand Department of Conservation show trends of decline. Despite being one of New Zealand’s most threatened grasshopper species, little research has been directed toward maximising conservation outcomes for B. robustus.

The first objective of this research was to understand the life history of B. robustus. Grasshoppers were tracked from egg to adulthood in captivity in the field and in the laboratory. The life cycle of B. robustus was observed to be ~27 months in the field. Females laid on average 1.3 egg pods in the wild, but up to 8 in the laboratory. Egg pods contained between 17 and 35 eggs, and the eggs go through an obligate diapause which is almost certainly broken by cold winter temperatures below 0 °C. Survivorship was low in the laboratory and in the field, despite no predation pressure from key predators including birds and mammals. Understanding the life history of B. robustus has facilitated the interpretation of trends detected during population monitoring, informed the development of captive rearing for release protocols, and provided an opportunity to simulate expected outcomes of future translocations.

The second research objective was to understand the habitat requirements of B. robustus. Using miniaturised radio transmitters, the movements of adult female grasshoppers occupying a linear gravel road were compared to those occupying a more natural open braided river habitat. Dense vegetation was found to be unfavourable habitat, indicating that management of vegetation will be important for maintaining habitat quality. No difference in home-range size was found between the two sites indicating that the area of habitat required to support an adult female is likely to be > 300 m2. This has applications for managing remaining habitat (e.g. area over which management of weed and mammalian predators should be implemented), creating artificial habitat, and selecting potential receiving habitats for conservation translocations.

The third research objective of the current study was to evaluate the threat introduced mammalian predators pose to the persistence of B. robustus. The outcome of an experimental translocation where individuals were released into predator reduced and non-predator reduced areas was monitored. In addition, long-term trends were analysed of three populations of another declining dryland grasshopper species, Sigaus minutus, that are present in areas where mammalian predators are controlled at different levels of intensity. It was concluded that mammalian predators are likely to pose a substantial threat to B. robustus, and that high intensity mammalian predator control across the full suite of predators should be prioritised to improve conservation management and translocation success.

The fourth research object was to develop effective monitoring techniques for B. robustus. First, an intensive removal sampling study conducted over a single active season (November to March) was used to rapidly quantify seasonal and demographic variation in visual detectability of B. robustus. Juvenile instars were found to dominate population composition in all months except December (adults = 69 %) and males represented > 50 % of monthly captures. Adult females were 2-3 times larger than adult males, and 79 % of those captured were found during the first search of an area, compared to only 52 % of adult males. The odds of detecting an individual were found to increase by 6 % per 1 mm of body length. Second, by conducting experimental monitoring for three consecutive seasons, both population density and population distribution monitoring protocols were developed for B. robustus. The recommended population density monitoring protocol used adult female counts as an index of population size to maximise visual detectability and ensure data is biologically meaningful. November and early December was found to be the most appropriate time to conduct monitoring, and > 20 transect replicates with > 4 survey replicates each were required to detect a significant change in adult female population size with power > 0.8. Occupancy modelling was investigated as a distribution monitoring protocol for B. robustus by estimating the probability of detection (pg) in a natural open riverbed compared to a gravel road habitat. Detection of grasshopper presence was found to be high (pg > 0.6) when using a 100 m x 1 m transect in both habitat types under optimal (no cloud) conditions in February, and a minimum of 3 visits per season was required to have confidence in trend detection. Implementing the population monitoring protocol presented here will be important for measuring the outcome of any future translocations of B. robustus.

This research has contributed knowledge that has substantially advanced the understanding of a Nationally Endangered insect. It has provided evidence-based conservation management recommendations that contribute toward the development of conservation translocation as a successful and valuable tool for preventing future insect extinctions.