In many ecosystems food-web dynamics are driven by spatial and temporal variation in the availability of sugar resources, which form the primary or even exclusive dietary constituents for many species. Scale insects (Hemiptera) produce sugar-rich honeydew, which can be a keystone sugar source in honeydew ecosystems worldwide. In New Zealand, most previous research in honeydew ecosystems has been conducted in areas where herpetofauna are heavily suppressed by introduced predators. Consequently, little is known about potential trophic interactions between endemic lizards and scale insects.
Honeydew production by New Zealand beech scale insects (Ultracoelostoma spp., Hemiptera: Margarodidae) is widely considered to have a positive influence on native animal abundance and ecosystem functioning. As a first assessment of whether there is a positive relationship between honeydew throughfall and litter decomposition rates, we placed experimental litter bags in each of 10 high and 10 low honeydew plots in mixed southern beech (Nothofagus) forest at each of two sites, Lakehead and Rotoiti, in the Nelson Lakes National Park.
We describe a simple gravimetric technique for measuring the standing crop or production of carbohydrate-rich solutions such as honeydew or nectar. Simulated honeydew was sampled by absorbing droplets of solutions of known concentration and volume with dried and weighed pieces of filter paper. The change in mass of the paper after redrying provides an estimate of the total solution carbohydrates. This method was compared with a widely-used technique, whereby the volume and concentration of droplets is measured with microcapillary tubes and a sugar refractometer.
Honeydew excreted by phloem-sap sucking scale insects (Ultracoelostoma sp.) living in the bark of beech (Nothofagus solandri:) trees growing at a high elevation (900 m) site in the Craigieburn range of Canterbury, New Zealand, was measured over four days during 110 May 1996. Average standing crop of honeydew sugar was 3.1 mg m-2, and ranged from 0.4 to 5.5 mg m-2. Daily production of honeydew sugar ranged from 0.2 to 1.5 mg insect-1 24 h-1, and 4.1 to 45.9 mg m-2 24 h-1.
To examine the seasonal availability of the major bellbird (Anthornis melanura) food sources in a mountain beech (Nothofagus solandrivar. cliffortioides) forest at Craigieburn, the invertebrate, honeydew, and mistletoe (Peraxilla tetrapetala and Alepis flavida) fruit and nectar resources were sampled over 12 months. The total available food varied 2.6-fold from a low in October (8798 kJ/ha) to a high in December (22,959 kJ/ha) with an annual mean of 15,782 kJ/ha.
The effect of honeydew density on arthropod community structure was investigated in the Nothofagus forest of Nelson Lakes National Park, New Zealand. Pitfall trapping revealed no community response to honeydew density, whereas sticky trapping showed the community composition of trunk-dwelling arthropods varied along a honeydew gradient. Mycetophilidae, Staphylinidae, Pteromalidae and Margarodidae were classified as high honeydew biased, while Diapriidae and Platygasteridae were non-honeydew biased.
Introduced common wasps (Vespula vulgaris) are widespread, abundant pests in New Zealand. They compete for food with native birds and feed on native invertebrates. We poisoned wasps annually over 4 years to see if it was possible to reduce their abundance in two 30-ha beech forest sites. Two different poisons (sodium monofluoroacetate and sulfluramid) were used, mixed with sardine catfood. There was no evidence that one poison was more effective than the other.
The relationship between fleshy-fruited indigenous species and adventive weeds in the diet of 500 mist-netted birds was studied in forest remnants of differing size and degree of modification. Fruit abundance Peaked in March and April, and most fruit was either red/orange or purple/black. The physical parameters of adventive and indigenous fruits were not significantly different. Six of the 15 passerine species netted are frugivores, and of those netted 77% had eaten fruit.
Honeydew, the sugary exudate of the scale insect Ultracoelostoma brittini, is an important food source in black beech (Nothofagus solandri var. solandri) forests in the South Island of New Zealand. Two of the most prominent foragers of honeydew are honey bees (Apis mellifera) and wasps (Vespula germanica and V. vulgaris). Observations in the field and using a captive bee hive were used to investigate competition between bees and wasps feeding on honeydew.
Prey collected by Vespula vulgaris and V. germanica were sampled by intercepting foragers returning to nests at two sites in scrubland-pasture near Hamilton. About 12% of returning foragers carried animal prey and 5% carried wood pulp. The remaining 83% carried no external load. The most common prey item for both species was Diptera, followed by Lepidoptera and Araneae (spiders). Even in similar habitats the two species collected different prey, with V. germanica collecting more Diptera and V. vulgaris more Lepidoptera.