Danny Thornburrow

Beetle community changes following pest mammal control at two biodiversity sanctuaries in Wellington, New Zealand

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-Wiltons 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-Wiltons 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 monitoring, including reconstructing fossil invertebrate communities to sharpen restoration objectives.

Beetle community responses to grey willow (Salix cinerea) invasion within three New Zealand wetlands

Abstract 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 significantly between grey willow-dominated vegetation and native wetland vegetation. These compositional differences were mainly due to the increasing complexity of vegetation structure following grey willow invasion. The beetle communities within restored native wetland vegetation were most similar to those within the native wetland vegetation. From a conservation perspective, these results are encouraging and suggest that, although grey willows dramatically alter the composition of beetle communities present, these communities can be restored to a beetle fauna that is similar to those found within native wetland through the removal of the willows.

Habitat use, Behavior and Movement Patterns of a Threatened New Zealand Giant Weta, Deinacrida heteracantha (Anostostomatidae: Orthoptera)

Abstract Wetapunga (Deinacrida heteracantha), New Zealands 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. Wetapunga were generally solitary and the majority of their activities, such as feeding, movements and oviposition, occurred at night. The one exception is mating (actual copulation and pre-, post-copulatory behavior), which usually occurred during daylight after weta had paired during the previous night. During the study, one male wetapunga was eaten by an unknown avian predator. Radiotelemetry has extended our knowledge of adult wetapunga behavior and this monitoring technique could be readily applied to other large invertebrates.

Morphometric change, distribution, and habitat use of Cook Strait giant weta (Deinacrida rugosa: Orthoptera: Anastostomatidae) after translocation to Matiu-Somes Island

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 juveniles were also found, and large juveniles were common in September and December. Weta have spread throughout the island but were abundant over the northern half of the island with few found at the southern end. Adults and large juveniles were usually found on or near the ground whereas small juveniles were above ground on vegetation. Most adult weta were seen during the fi rst two hours of darkness in February on the ground or on short grass, and only five were on bushes. Overall, 22% of adults were injured, usually with damaged antennae or legs. Cook Strait giant weta are now so well established on Matiu-Somes Island that we consider this translocation a success.

Sampling the invertebrate community associated with a threatened wetland plant, Sporadanthus ferrugineus, using a new design of emergence trap

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 species of Agromyzidae (Diptera), and the beetle Selenopalpus cyaneus (Oedemeridae: Coleoptera). The trap was effective at capturing Houdinia flexilissima (Lepidoptera), a strictly monophagous species specialized to feed in the narrow stems of S. ferrugineus. The advantages of this trap design are the relatively low construction cost, and ease of installation and transportation. Its potential for use in control programmes and other ecological studies is discussed.

Population history and genetic bottlenecks in translocated Cook Strait giant weta, Deinacrida rugosa: recommendations for future conservation management

Abstract 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.