Richard J. Toft

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.

Reducing predation of orb-web spiders by controlling common wasps (Vespula vulgaris) in a New Zealand beech forest

1. Introduced common wasps (Vespula vulgaris) reach high densities in the beech forests (Nothofagus spp.) of the northern South Island, New Zealand, and may be having a severe impact on populations of native invertebrates. An experimental approach was used to test whether reducing the abundance of common wasps increases the probability of native invertebrates surviving. Garden orb‐web spiders (Eriophora pustulosa) were used because they were easy to collect and could be trained to build webs on a standard frame. Thirty orb‐web spiders were placed out on web‐frames in each of four study sites in beech forest during periods of low, medium and high wasp abundance, and their rate of removal was measured over a 4‐h period. Wasp numbers were reduced by poisoning in two study sites. Using wasp‐abundance data from weekly Malaise trap samples in the poisoned and non‐poisoned sites, the probability of spider survival over the entire wasp season was modelled and the level of wasp control necessary to protect natural populations of orb‐web spiders was estimated.

Impacts of the weed Tradescantia fluminensis on insect communities in fragmented forests in New Zealand

Abstract The impact of the weed Tradescantia fluminensis on insect communities, as represented by Malaise-trapped beetles (Coleoptera) and fungus gnats (Diptera: Mycetophilidae s. l.), was studied in three forest fragments. Each fragment contained three plots with and without a dense weed cover. Data on vegetation and habitat variables were collected. Twinspan and Decorana analyses separated the plots by fragment for fungus gnat communities, and nearly so for the presence/absence of beetle species. The fungus gnat communities separated into plots with and without tradescantia at two sites, and there were fewer species of fungus gnats and beetles in tradescantia plots at the site with the simplest habitat structure. The richness of beetle and fungus gnat species was correlated with vascular plant richness. As tradescantia is known to prevent regeneration of many native plants, we predict a corresponding decline in invertebrate diversity and fragment complementarity where the weed is established.

Establishment of the wasp parasitoid, Sphecophaga vesparum (Hymenoptera: Ichneumonidae), in New Zealand

AbstractThe parasitoid Sphecophaga vesparum (Hymenoptera: Ichneumonidae), has been released throughout New Zealand in an attempt to control introduced common (Vespula vulgaris) and German wasps (V. germanica) (Hymenoptera: Vespidae).The parasitoid overwintered and has probably become established at Pelorus Bridge, 25 km east of Nelson. In 1990, an infested nest was recovered 7.1 km from this release site, indicating that the parasitoid can disperse at least 2.37 km per year. However, the proportion of nests parasitised at Pelorus Bridge has increased only slightly in the first 3 years after release.No Sphecophaga were recovered from 1190 nests at 38 other sites where they were released and monitored. This may reflect the small number of parasitoids that emerged at some sites, the small number of nests inspected at others, or a low parasitoid population density. However, combined data from this and other studies suggests that the parasitoid is having difficulty in becoming established in many areas. It is ...

Assessing the risk of invasive ants: a simple and flexible scorecard approach

Abstract.Numerous ant species are being transported around globe through international trade, many of which become invasive. To mitigate the potential impacts of invasive ant species, an assessment system is needed which is simple, can be tailored for specific-user and regional requirements, and has the potential to integrate a variety of additional information. Here we present such a system, which has been used in New Zealand to determine which ant species pose the greatest threat to natural ecosystems. However, the scorecard system could be applied widely around the globe for assessing the threat of invasive ant species.

Seasonality of crane flies (Diptera: Tipulidae) in South Island beech forest in relation to the abundance of Vespula wasps (Hymenoptera: Vespidae)

Crane flies (Tipulidae) are common in the diet of native insectivores and introduced Vespula wasps. The seasonality of adult crane fly species was determined by Malaise trapping so that species potentially vulnerable to an impact from high wasp numbers could be identified as possible indicator species for analyzing the wider impacts of wasps in beech forest (Nothofagus spp.) ecosystems. Four sites in beech forest at Lake Rotoroa, Nelson Lakes National Park, were sampled over 2.5 years. The seasonality of 20 species of larger Tipulidae were plotted against three broad seasonal levels of wasp abundance identified from Malaise trap catches. Eleven species shared at least 40% of their flight period with high wasp numbers, with three of these restricted almost entirely to the period of high wasp abundance. These species may be the most vulnerable to an impact from wasp predation.

Flowers, phenology and pollination of the endemic New Zealand greenhood orchid Pterostylis brumalis

ABSTRACT Greenhood orchids are most diverse in New Zealand and Australia, with at least some species pollinated by sexual deception of male fungus gnats. Preliminary investigation of endemic New Zealand Pterostylis brumalis via field phenology, hand-pollination and insect trapping revealed P. brumalis is self-compatible but relies on insects for cross pollination. Natural fruit-set was low, averaging 2.6% across two populations. High fruit-set in hand-pollinated flowers (66.7%) indicates severe pollinator limitation. In comparison, only one collected insect, a female Mycetophila vulgaris, bore orchid pollinia. Potential pollinator attractants (colour and scent) were analysed. UV reflectance may enhance pollinator detection of the flower against the background, but visual modelling generated conflicting results: a categorical fly vision model indicated excellent camouflage against herbivory, but a generic tetrachromat vision model suggested flowers are easily distinguishable against the background. Both models have flaws that create issues with drawing conclusions, and identification of the pollinator is required to understand their visual system further. Scanning electron microscopy (SEM) revealed putative scent-releasing osmophores (lateral sepals) and uniform papillate trichomes (labellum) that may mechanically direct pollinators into the floral trap. The trap is a pressure sensitive labellum that temporarily traps the visitor inside the flower.

Three introduced species of Mycetophilidae (Diptera: Sciaroidea) established in New Zealand

The presence of introduced fungus gnats (Diptera: Mycetophilidae) in New Zealand has gone largely unnoticed due to a lengthy period with little research on this group, and a lack of generalised collecting in urban areas. Leia arsona, Sciophila parviareolata, and S. ocreata are reported in New Zealand for the first time.The first two species are widespread in anthropogenic habitats and have been established for more than 20 years. The third species is known from a single urban locality, suggesting it is a more recent introduction.