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Predation by introduced mammals frequently limits abundance of New Zealand’s native invertebrates. We investigated responses of beetle and wētā communities to mammal eradication at two fenced fores...

Translocating populations of endangered animals to predator-free offshore islands is an extreme, and potentially risky, conservation management strategy. There are many examples of failures and successes, however relatively little work has been done to formally quantify the required numbers of translocated individuals to increase the chance of successful establishment. Cook Strait giant weta, Deinacrida rugosa Buller 1870 (Orthoptera: Anostostomatidae), of New Zealand are an example of an at-risk species where extreme conservation measures are needed, due to their ground-dwelling lifestyle making them particularly prone to habitat loss and predation by alien species following human settlement. Here, we have used microsatellite markers to characterise genetic diversity within and between two parental populations (Mana and Stephens Islands), and two translocated populations (Maud and Matiu/Somes Islands), and estimate probabilities of genetic bottlenecks. We have modelled various demographic scenarios to quantify the severity of effective population size fluctuations resulting from translocations using DIYABC, and explored the number of founders needed to retain rare alleles using ALLELERETAIN. Our results suggest that populations have expanded on both Maud Island and Matiu/Somes Island from effective population sizes at time of translocation of 36 and 47 respectively, but provide evidence for a genetic bottleneck on Maud Island. We also show that translocations have had minimal impact on parental effective population sizes. The impact of our results on future conservation management efforts is discussed.

Summary The use of herbicides to control weeds, particularly large invasions, has now become an essential management tool in many ecological restoration projects. The herbicide glyphosate is routinely used to control the invasive weed, Grey Willow (Salix cinerea), within New Zealand wetlands. However, little is known about the effects of glyphosate on invertebrates. We determine the short-term effects of glyphosate on the abundance and composition of the nontarget canopy invertebrate community in wetlands invaded by Grey Willow in New Zealand. Initially, the application of glyphosate and a surfactant showed no detectable effect on the canopy invertebrates examined in this study. However, 27 days after herbicide application, significant Grey Willow canopy loss caused dramatic decreases in the abundance of invertebrates in the glyphosate-treated plots compared with the unsprayed plots. Invertebrates appeared to be sensitive to changes in vegetation structure, such as canopy loss. These results agree with previous studies that have shown that the negative impacts of glyphosate on invertebrate communities are related to indirect effects via habitat modification as the herbicide-treated vegetation dies. From a terrestrial invertebrate perspective, this study suggests that the use of glyphosate herbicide is suitable for the control of invasive weeds within wetland restoration projects as it appears to have negligible impact on the canopy invertebrate assemblage.

Wētā, large wingless anostostomatid orthopterans, have been the most frequently translocated insects in New Zealand. Until recently, such translocations were only monitored intermittently to confirm presence. We investigate the spread of Cook Strait giant wētā (Deinacrida rugosa Buller, 1871) after its release on Matiu/Somes Island, Wellington, New Zealand, in 1996. Adult wētā were surveyed from 2008 to 2016 using footprint tracking tunnels and/or searching with spotlights at night. The population underwent a reversal in distributional abundance after 2008. In 2008, they were abundant in the north and rare in the south but by 2013 and 2015 they were relatively less abundant in the north and common in the south. Why they diminished in the north remains unknown but possible causes are predation on juvenile wētā by nocturnal geckos (detected in the north and east but not in the south), by some habitat change (mostly reduction of some lawn), or by a combination of these together with removal of wētā from the north for translocation elsewhere. Further research is required to confirm which of these factors affect wētā abundance, if there are other causes, and if any further change in distributional abundance occurs.

Non-native invasive plants are a significant threat to native biodiversity as they change community structure and ecosystem processes and it is becoming imperative that these invasive plants are controlled. We investigated the response of wetland invertebrates to glyphosate chemical control of an introduced tree, grey willow (Salix cinerea), in a before-after-control-impact (BACI) experiment within a New Zealand wetland. Our findings suggest that control of grey willow resulted in significant increases in the abundance of invertebrates within 2 years after herbicide application. Analysis of beetle communities revealed that the abundance and species richness of herbivorous and predacious beetles, the abundance of introduced species, and the species richness of native and introduced species were all significantly higher in the herbicide-treated plots than in the unsprayed plots. The composition of the beetle community separated into two clear groups—plots before spray/no spray and plots 1 and 2 years after herbicide application. We suggest that the beetle compositional changes were driven by complex changes in vegetation associated with the canopy collapse of grey willow trees and the initial influx of introduced plant species, predominantly weedy annuals and perennials, after willow control. Restoration via invasive plant control can promote the reestablishment of invertebrate communities typical of native wetlands, but their long-term sustainability is contingent on prevention of grey willow reinvasion and reestablishment of the native plant habitat.

The Mercury Islands tusked weta, Motuweta isolata (Orthoptera: Anostostomatidae), survived only on 13 ha Ahu or Middle Island, a mammal-free island in the Mercury Group, New Zealand. Between 2000 and 2009, 567 individuals were translocated in nine releases to six nearby islands from which mammals had been removed. These translocations occurred to reduce the chance of accidental extinction of the Middle Island population of only a few hundred adults and to contribute to the restoration of the other islands. All translocated insects originated from the captive-bred progeny of one male and two females collected from Middle Island between 1998 and 2001. Their establishment on Double and Red Mercury Islands, after their releases in 2000 and 2001 respectively, was confirmed by searching plots, and by using footprint tracking tunnels on Red Mercury Island between 2008 and 2012. Tracking tunnels provided better data and proved more cost effective than searching plots for detecting large tusked weta. Tracking tunnels demonstrated that the population on Red Mercury expanded outwards from the release sites by 50–100 m each year between 2009 and 2012. These weta are now estimated to be present over more than half the Island. Tusked weta have also survived on Stanley, Korapuki and Ohinau Islands after releases in 2007, but they remain within 100 m of the release sites. No confirmed progeny of the weta released on Cuvier Island in 2008 and 2011 were detected. No tusked weta were detected on Middle Island using tracking tunnels on eight occasions between 2009 and 2012, suggesting this species is likely to be locally extinct. Despite possible failure on one island, these translocations have resulted in a significant conservation success outcome.

Introduced pest mammals impact widely on New Zealand invertebrates, but community-level responses to mammal removal are largely unmeasured. Beetles were pitfall-trapped for 7–10 years to examine how their communities responded to near eradication of all mammals except mice (Mus musculus) within a fenced sanctuary (Zealandia), and to sustained mammal control at an unfenced sanctuary (Otari-Wilton's Bush). In Zealandia, beetle abundance unexpectedly declined for 6 years after mammal eradication before stabilising. Beetle community composition changed, perhaps due to increased predation by birds and mice, but species richness, size distribution and trophic composition did not. At Otari-Wilton's Bush, beetle abundance also declined, in the presence of few but diverse mammals. Identifying causes of invertebrate community changes will be improved with study replication, more ‘before’ data, and targeted measurement of possible explanatory factors. Five recommendations are made for future insect community monitor...

There are few suitable monitoring tools for assessing the effectiveness of management for threatened insect taxa. This is especially true for cryptic arboreal species of nocturnal flightless orthopterans in the genus Deinacrida from New Zealand. Systematic searching of habitat during the day was compared with footprint tracking tunnels baited with peanut butter as methods for monitoring the arboreal giant weta Deinacrida heteracantha and Deinacrida mahoenui (Orthoptera: Anostostomatidae). Searching by day required more time (3h per transect) than operating tracking tunnels (1.4h). Lines of 30–35 tracking tunnels spaced 30 m apart could be quickly set to sample large areas. Searching may provide additional information including the species, age class, and sex, whereas tracking tunnels yield presence/absence data for giant weta that were larger than other anostostomatid present. Both methods provide indices of relative abundance: it is impractical in tall forest to accurately estimate absolute density whereas tracking tunnel results are related to the activity of weta. Weta activity may depend on vapour pressure deficit modulated by the temperature. For conservation and monitoring purposes, we recommend that tracking tunnels be used first to detect giant weta and only then search for them if further data is required.

A 5-year litterbag study examined decomposition rates at four sites representing restiad peatland succession in Waikato, New Zealand. Early successional sites were dominated by Baumea rubiginosa, or Leptospermum scoparium, mid-successional by Empodisma robustum, and late successional by Sporadanthus ferrugineus. Leaf/culm materials from these species were placed on the surface, and roots of Empodisma and Sporadanthus buried at depths of 5, 25, and 55 cm to test the influence of succession on species and site decomposition rates. Typha latifolia leaves from a Canadian bog were placed at the surface and three depths to allow comparisons with northern peatlands. Litterbags were retrieved after 0.5, 1, 2, 3, 4, and 5 years, and mass remaining characterized by an exponential model k value. Surface litter k values (0.12–0.80 y−1) decreased from early to late successional species; however, decomposition was slower at more waterlogged early successional sites. Buried litter k values (0.04–0.24 y−1) decreased with depth and increased from early to late successional sites, with Empodisma roots having the slowest rates. Few strong relationships existed between litter quality and decomposition rates. In contrast, water table regime strongly influenced decomposition rates; k values for the “standard” Typha litter decreased exponentially as period of saturation increased, irrespective of site successional status, nutrients, or other factors. Lower water tables in the more aerated later successional sites have led to faster decomposition rates. Ongoing drainage combined with the potential impacts of climate change may increase organic matter decomposition and accelerate carbon release into the atmosphere.

We investigated the effects of invasion by introduced grey willow (Salix cinerea) on beetle communities within four wetland vegetation types: native vegetation, native vegetation following grey willow removal, native vegetation undergoing grey willow invasion and dense grey willow-dominated vegetation. In total, 1505 beetles from 90 species were collected using modified Malaise traps. Native wetland vegetation had significantly lower beetle species richness than willow-dominated vegetation and was dominated by herbivores, whereas detritivores characterised willow-dominated vegetation. Beetle abundance was highest in the willow-dominated vegetation and mostly comprised detritivores. In contrast, beetle abundance was lowest in native wetland vegetation, but had even proportions of herbivores and detritivores. Native wetland vegetation had a high proportion of native beetles present. As grey willows invaded, introduced beetles became more common. The beetle community composition differed significant...

Giant weta (Orthoptera: Anostostomatidae) are large flightless New Zealand insects vulnerable to predation from introduced mammals. Some species have been transferred to islands or mammal-free mainland sanctuaries to establish additional populations. Radiotelemetry was used to investigate behaviour, movements and survival of adult Cook Strait giant weta (Deinacrida rugosa) immediately after translocation into Karori Sanctuary, New Zealand, to describe their initial movements, and to assess the importance of this establishment phase in relation to the long-term viability of the population. The average distance moved between consecutive daytime refuges for translocated male D. rugosa within Karori Sanctuary was significantly further than for resident weta on Matiu-Somes Island. In contrast, translocated female weta moved significantly smaller distances between consecutive daytime refuges within Karori Sanctuary than those on Matiu-Somes Island. Translocated D. rugosa travelled significantly further between consecutive daytime refuges between 19 and 45 days after release than during the first 19 days and more than 45 days of radiotracking. Deinacrida rugosa survived well following translocation and there was only limited evidence of predation despite an increased abundance of indigenous avian and reptilian predators being present, and the presence of low numbers of mice. The establishment potential of this population was not adversely affected by movements and survival of the weta immediately after translocation. It still remains to be seen if a self-sustaining population of D. rugosa develops in Karori Sanctuary but the indications are that the species is present because progeny of the translocated weta are regularly seen within Karori Sanctuary. Radiotelemetry provided valuable insights into the behaviour of adult D. rugosa and it could be appropriate for monitoring other large bodied invertebrates.

Wetapunga (Deinacrida heteracantha), New Zealand's largest insect, were formerly abundant in forests of northern New Zealand. However, they are now restricted to onepopulation on mammal-free Little Barrier Island (3083 ha). This study investigated the movements, habitat use and behavior of 22 adult wetapunga fitted with miniature radiotransmitters for up to 18 nights. Adult wetapunga appeared to be quite mobile, with males (16 m per night) moving further than females (8 m per night). Differences in the distances travelled by adult male and female wetapunga between daytime refuges appear due to differences in reproductive behavior. Wetapunga were associated with silverfern, nikau palm, kanuka, and kohekohe within second-growth coastal forest on Little Barrier Island. The majority of wetapunga were found above ground level, but were also occasionally found moving on the ground. In addition, adult wetapunga were found in relatively open sites with little or no cover and were clearly visible by day. ...

Appropriate monitoring tools are essential for assessing the effectiveness of management for all threatened insect taxa. In New Zealand the large-bodied flightless orthopterans in the genus Deinacrida have mostly been monitored by searching through habitat during the day or spotlighting at night but this is time consuming and the results depend on the skill of the searcher. Recently, footprint tracking tunnels, similar to those used for monitoring small mammals in New Zealand, were found to be effective for detecting adults of various giant weta species. In this study, we compared the abundance of Cook Strait giant weta (CSGW) in the vicinity of the tunnels, estimated by mark-recapture, with the number of tracking tunnels tracked by weta. We found strong indications that both baited and unbaited tracking tunnels can be used to estimate the number of adult weta present but that this probably depends on their responses to meteorological conditions which are not yet understood. Our results also show that footprint tracking tunnels are more effective for detecting adult CSGW than searching for these insects at night and that baiting tracking tunnels with peanut butter increases their effectiveness for detecting adult CSGW. We confirmed how far Cook Strait giant weta moved each night on Matiu-Somes Island by attaching transmitters to them and found that day roosts of three adult males were on average 8.6 m apart each day and those of adult females were on average 21.3 m apart. Both the low recapture rates of marked adult CSGW and the nightly displacements of those with transmitters suggest that adult CSGW show no site fidelity and are clearly capable of moving large distances each night. However, an individual weta is unlikely to track more than one tunnel per night if tunnels are 30 m apart. Tracking tunnels have the potential to be used with some other insects, provided their footprints are diagnostic. An advantage of using tracking tunnels is that they are non-lethal and would therefore be particularly suitable for monitoring other large threatened insect taxa.

Giant weta (Orthoptera: Anostostomatidae) are large flightless New Zealand insects in the genus Deinacrida. They usually survive in the absence of introduced rats and many have now been transferred to islands and areas after rodent eradications. One such transfer of the Cook Strait giant weta, D. rugosa was made from Mana Island to Matiu-Somes Island in 1996 and we investigated the sex ratio, morphometrics, growth, distribution, habitat use, nocturnal activity pattern and incidence of natural injury in February, May, September and December 2007 and February 2008. Most weta found were adults (82%), more adult females (74%) were seen than males but more male juveniles (61%) were seen than females. Weta from Matiu-Somes Island had slightly longer metatibiae than those from Mana Island. Cohorts of different-sized insects become larger in most successive samples indicating a 2-year development period following eclosion. Adults were always present but were most frequently seen in February when the smallest juve...

There have been numerous transfers of the large-bodied orthopteran, the Mahoenui giant weta (Family Anostostomatidae: Deinacrida mahoenui), over the past 19 years but there has been limited follow-up monitoring to ascertain establishment and breeding of transferred populations. Recent surveys carried out at all the locations where this weta were transferred, found weta at four of the seven transferred sites. The most important factor determining the success of past transfers is the absence of introduced mammalian predators, particularly rats, at a site. At two sites, Mahurangi Island Scenic Reserve and Warrenheip, weta appeared to be flourishing and have successfully established new populations in the absence of rats. If mammals are present at a site, the occurrence of dense prickly gorse to protect giant weta from predation is another important factor in their survival. Weta were found at very low densities (only single specimens were captured) at Mangaokewa Scenic Reserve and Tikikaru (private land) and it is likely their populations are not viable in the long term. Further efforts to establish Mahoenui giant weta populations should be in mammal-free sanctuaries containing native forest. More intensive post-transfer monitoring using radio-transmitters would enable better understanding of their behaviour after transfer. In addition, long-term regular monitoring of transferred populations is required, particularly those where the likelihood of rat re-invasion is high.

A novel design of emergence trap was used to examine the invertebrate fauna associated with Sporadanthus ferrugineus, a threatened wetland plant. Potted S. ferrugineus plants were placed in sealed emergence traps after 6, 12 and 18 weeks exposure to invertebrates in an undisturbed peat bog at Torehape, North Island, New Zealand. A total of 1,137 individuals from 42 species in seven invertebrate Orders colonized 30 S. ferrugineus plants and were captured within the emergence traps. The invertebrate densities did not change signifi cantly during the short duration of the experiment, or with increasing distance into the undisturbed peat bog. In contrast, total species richness caught in each emergence trap increased signifi cantly during the course of the experiment. The most common species captured was the aphid Rhopalosiphum rufiabdominalis (Aphididae: Homoptera), accounting for 24% of total abundance. Other common species caught included the spider Anateropsis hilaris (Lycosidae: Araneae), an unidentified...