Jacqueline R. Beggs

The role of introduced predators and competitors in the decline of Kaka (Nestor meridionalis) populations in New Zealand

We investigated the role of introduced predators and competitors in the population decline of kaka, Nestor meridionalis, a previously abundant forest parrot endemic to New Zealand. We provided supplementary food to test if a shortage of high energy food was limiting breeding in kaka. However, because most nesting attempts suffered from predation and we could not establish a non-treatment area, the role of competitors is still unclear. Kaka only bred in years when beech (Nothofagus) seeded. Over 11 years and 20 breeding attempts we recorded only four fledglings surviving to independence. Nine young kaka and four adult females were killed on the nest. We suggest that stoats were predominantly responsible for this predation. Kaka are relatively common on offshore islands without stoats, even in the presence of other predators and competitors, but are scarce on all islands containing stoats. We predict that stoat predation will cause kaka to become extinct on mainland New Zealand unless stoats and/or kaka are managed.

Ecological effects and management of invasive alien Vespidae

Insect species associated with human goods continue to be accidentally introduced into new locations. A small proportion of these introduced species become invasive, causing a range of impacts in the receiving community. It is therefore important to evaluate the patterns of which species become invasive and which strategies are most successful in managing them. This review assesses the distribution, abundance, impact and management of the invasive Vespidae worldwide. We identified 34 vespid species known to be introduced around the world, but the seven most invasive species are all eusocial. Most introduced Vespidae only occur in one or two countries, but some areas have become geographic hotspots of invasion: Hawaii (15 species), North America (eight species), New Zealand (five species), Australia (four species) and South America (four species). Two invasive species, Vespula vulgaris and V. germanica have become particularly widespread and abundant with a range of impacts on biodiversity and ecosystem function. Other successful invasive species include several Polistes spp., which affect local biodiversity through direct predation or competition for food or space. Toxic baiting has been the most successful control strategy against invasive vespids to date, although this has mostly been small scale experimental management as it has proved difficult to develop commercial control products. Development of shelf-stable lures or baits combined with suitable toxins or pathogens could overcome some of the commercial impediments. Several attempts at biological control using parasitoids have not successfully reduced invasive wasp populations, although the biocontrol agent has only established in one case. The social structure of colonies and their high reproductive efficiency have facilitated invasion by these species, but it also means management at the population level will be difficult. This emphasises the need to prevent such invasions from occurring in the first place.

The Kaka Nestor meridionalis, a New Zealand parrot endangered by introduced wasps and mammals

Abstract The kaka Nestor meridionalis is a forest parrot endemic to New Zealand, whose numbers have declined this century. We measured the energetics and breeding success of a remnant population of the South Island subspecies N.m. meridionalis in a beech Nothofagus forest modified by introduced browsing mammals. In six years only one successful kaka nest was found, and we suggest that a shortage of food with a high net energy return is limiting reproductive success. In summer, kaka obtained most of their daily energy requirements from honeydew excreted by the scale insect Ultracoelostomaa assimile , but in autumn this was no longer available. Introduced wasps Vespula spp. build up to plague proportions in autumn, and consumed most of the honeydew. The only female kaka to breed successfully was subsequently killed by a stoat Mustela erminea . We predict a decline in the density of South Island kaka in beech forests.

Restructuring of Lepidoptera communities by introduced Vespula wasps in a New Zealand beech forest

Abstract Introduced social wasps (Vespula vulgaris) reach high densities in some New Zealand beech forests, because honeydew provides an abundant high-energy food source. We manipulated wasp density to estimate an “ecological damage threshold” for large, free-living Lepidoptera larvae. There will be a continuum of ecological damage thresholds for wasp density depending on the prey species or habitat. Experimentally placed small caterpillars had a significantly higher survival rate than large caterpillars, and the survival rate of both groups decreased with increasing wasp density. Spring-occurring caterpillars have a probability of surviving of 0.90–0.95, assuming wasps are the only source of mortality. However, at the peak of the wasp season we predict caterpillars would have virtually no chance (probability of 10−78 to 10−40) of surviving to adults. Wasp abundance must be reduced by at least 88% to conserve the more vulnerable species of free-living caterpillars at wasp densities similar to those observed in our study sites. This equates to a damage threshold of 2.7 wasps per Malaise trap per day. It was exceeded for about 5 months of the year in non-poisoned sites. There are currently no biological or chemical control techniques available in New Zealand that will reduce wasp abundance below this damage threshold throughout the year. Our models show that most Lepidoptera with spring caterpillars will be able to persist, but species with caterpillars occurring in the peak wasp season will be eliminated.

Supplementary feeding restructures urban bird communities

Significance Bird feeding is essentially a massive global supplementary feeding experiment, yet few studies have attempted to explore its ecological effects. In this study we use an in situ experimental approach to investigate the impacts of bird feeding on the structure of local bird assemblages. We present vital evidence that bird feeding contributes to the bird community patterns we observe in urban areas. In particular, the study demonstrates that common feeding practices can encourage higher densities of introduced birds, with potential negative consequences for native birds. Food availability is a primary driver of avian population regulation. However, few studies have considered the effects of what is essentially a massive supplementary feeding experiment: the practice of wild bird feeding. Bird feeding has been posited as an important factor influencing the structure of bird communities, especially in urban areas, although experimental evidence to support this is almost entirely lacking. We carried out an 18-mo experimental feeding study at 23 residential properties to investigate the effects of bird feeding on local urban avian assemblages. Our feeding regime was based on predominant urban feeding practices in our region. We used monthly bird surveys to compare avian community composition, species richness, and the densities of local species at feeding and nonfeeding properties. Avian community structure diverged at feeding properties and five of the commonest garden bird species were affected by the experimental feeding regime. Introduced birds particularly benefitted, with dramatic increases observed in the abundances of house sparrow (Passer domesticus) and spotted dove (Streptopelia chinensis) in particular. We also found evidence of a negative effect on the abundance of a native insectivore, the grey warbler (Gerygone igata). Almost all of the observed changes did not persist once feeding had ceased. Our study directly demonstrates that the human pastime of bird feeding substantially contributes to the structure of avian community in urban areas, potentially altering the balance between native and introduced species.

A model for the effect of Sphecophaga vesparum vesparum as a biological control agent of the common wasp in New Zealand

1. A model of intermediate complexity is described to predict and understand the reasons for the ultimate impact of Sphecophaga vesparum vesparum (Hymenoptera : Ichneumonidae), introduced as a classical biological control agent of Vespula vulgaris (Hymenoptera : Vespidae) in New Zealand. The model was parameterized as far as possible from independent field data then fitted to the observed performance of the parasitoid over the first 5 years after release. 2. Wasp nest densities monitored over 5 years and seven sites in beech (Nothofagus spp.) forests averaged 12.2 ha -1 , with a maximum of 33 ha -1 . These are among the highest Vespula densities in the world. A Ricker model accounted for changes in nest density from year to year, giving a maximum ratio of increase in nest density of 3.3 per year and overcompensating density dependence at high densities, probably caused by queen competition and nest usurpation in spring. 3. The parasitoid has established at low levels in two sites, one of which has been studied in detail. Here parasitism levels (% autumn nests parasitized) have remained around 5% for 5 years, with a slight suggestion of an upward trend. 4. The model suggests that ultimate parasitism levels depend almost entirely on the parasitoids effective ratio of increase, R, defined as the maximum number of spring adults produced per spring adult (spanning several intermediate summer generations). Ultimate suppression of wasp nest densities depends on R, the rate of increase in parasitism within a year, and the mortality of parasitized early spring nests. The initial rate of build-up of parasitism additionally depends on the pattern of emergence of parasitoid cocoons, which may extend over 4 years. 5. R for S. vesparum vesparum at the site where it has established appears to be about 1.3-1.6, which is close to the lower limit of 1 for persistence. Such values suggest an ultimate suppression of wasp nest density and level of parasitism of about 10% and 25%, respectively. 6. The low value of R at this site and the parasitoids limited likely impact, appear to be due to a combination of delayed emergence of overwintering cocoons, low overwintering cocoon survival, and low production of cocoons per parasitized autumn nest. Additionally, a reduced or variable attack rate may contribute to the parasitoids lack of establishment at other sites, possibly due to poor synchrony between spring emergence of wasp queens and adult parasitoids. 7. A more successful parasitoid species or ecotype would need to have a higher R value, which requires cocoon emergence after 1 year rather than 2 or more, and/or higher values for the above parameters, particularly overwintering survival of cocoons. In addition, it would have to : act after the spring host density dependence ; cause a high (> 80%) mortality of parasitized spring nests ; and ideally also reduce queen output from autumn nests. An alternative to an agent causing mortality to spring nests would be a microbial one which significantly reduced queen fertility without impairing her competitive ability. 8. A 50% reduction in queen output from autumn nests, due to parasitism by S. vesparum vesparum, contributes little to host suppression because of its timing relative to host density dependence. If an alternative agent reduced wasp densities to a greater extent, the additional contribution of reduced queen output would become relatively more significant as density declined and the density dependence became less intense.

Carbohydrate analysis of beech honeydew

Abstract Honeydew from the beech scale insect, Ultracoelostoma assimile, infesting the beech species Nothofagus fusca and N. solandri var. solandri contained fructose, sucrose, glucose, and several non-reducing oligosaccharides composed of glucose and fructose residues. Although the total carbohydrate content varied from 5 to 64 g/100 g, and was dependent on rainfall in the sampling area, there were no significant differences between the honeydews of N. fusca and N. solandri sampled on the same day in the absence of recent rain. The mean proportional composition (±SD) of such samples were 42±5% fructose, 23±8% sucrose, 1 ± 0.4% glucose, and 33±6% oligosaccharides. A refractometer calibrated against sucrose slightly overestimated total carbohydrate of honeydew and such data should be divided by a correction factor of 1.145. The energy value of honeydew carbohydrate was estimated to be 16J mg−1 (dry weight). Honeydew contained little protein (<50 mg g−1).

Traffic rate as an index of colony size in Vespula wasps

AbstractThe number of Vespula wasp workers in a colony can be predicted from the mean of 1-minute counts of wasps entering or leaving the colony (traffic rate). The predictive equation (Adjusted R2 = 0.87) is: number of workers = 32.243 × traffic rate per minute and is independent of species, time of year, or location. However, we mainly measured mature colonies. The equation may overestimate the number of workers in spring colonies, because a greater proportion of workers forage then. Traffic rate can also predict the biomass of a V. vulgaris colony (Adjusted R2 = 0.90) by allowing for season. Colonies measured after mid May generally had a larger biomass for any given traffic rate than those measured earlier. There were too few data from V. germanica colonies to evaluate the relationship between traffic rate and biomass for this species.

Invasion success of the wasp parasitoid Sphecophaga vesparum vesparum (Curtis) in New Zealand

Abstract The wasp parasitoid Sphecophaga vesparum vesparum has been released in many parts of New Zealand since 1987 as a biological control agent for German (Vespula germanica) and common ( V. vulgaris) wasps. We checked whether the parasitoid had established at 33 release sites. At 26 of these sites, we inspected enough nests (at least 20) to be more than 80% certain that we would have detected the parasitoid if at least 8.5% of the nests had been attacked. We suggest that the probability of 5. v. vesparum successfully invading a site is greatly increased when a large number of founders are released and there is a high density of wasp nests. The parasitoid has established in at least two sites, Pelorus Bridge (Marlborough) and Ashley Forest (Canterbury). S. v. vesparum has been established at Pelorus Bridge since 1988 and annually infests an average of 8.5% of nests within 2 km of the release site. The parasitism rate has increased since the parasitoid first established. Despite this increase, we did no...

Changes in the distribution and proportions of Vespula vulgaris (L.) and Vespula germanica (Fab.) (Hymenoptera: Vespidae) between 1987 and 1990 in New Zealand

Abstract We collected more than 90 000 vespine wasps sent in by members of the public from throughout New Zealand between January 1987 and July 1991. Both the German wasp (established before 1950s) and the common wasp (established before 1980s) were widespread throughout most of the country in 1990. The common wasp had increased its distribution since 1987, mostly in the lower North Island and lower South Island, but was still absent from most of Northland, East Cape, and some regions of the central North Island and southern South Island. The common wasp had almost totally displaced the German wasp in honeydew beech forests by 1990 and accounted for a higher proportion of most samples from rural habitats. It had not completely displaced the German wasp in urban and other native forest habitats. It accounted for >50% of the vespulid population in the lower North Island and upper South Island. Its abundance had increased relative to German wasps where it was well established in 1987, as well as in locations...