Soluble carbon production by honeydew scale insects in a New Zealand beech forest

We estimated the annual production of honeydew per unit land area of beech (Nothofagus spp.) forest by measuring the amount of honeydew produced in 24 h by scale insects (Ultracoelostoma spp.) (Hemiptera: Margarodidae) every month for 2 years. We used exclosures to prevent animals (notably Vespula wasps) removing honeydew, and we compared the standing crop of honeydew inside permanently closed exclosures with that outside exclosures. Honeydew production and the number of honeydew droplets was highly variable between individual trees, tree type, position on tree, and, exclosure type, and within and between years. The amount of honeydew available outside exclosures was significantly reduced in year 2, predominantly by Vespula wasps, even though wasp density was relatively low. Sugar composition also varied between tree type and between years. Up to 5% of the sugar was glucose, with varying proportions of fructose, sucrose and oligosaccharides. The surface area of trees infested with scale insects was estimated using allometric regression relationships between tree diameter and total surface area of tree trunk and branch material. These estimates were combined with measurements of tree diameter in 10-m radius circular plots to give a production estimate of between 3500 and 4500 kg dry weight honeydew ha^-1 year^-1. Using this data, combined with previously published estimates of carbon uptake, it was estimated that between 6 and 8% of net primary productivity was released as honeydew. Honeydew scale insects provide large amounts of biologically available carbon in the form of soluble sugar. It is a crucial resource for the above-ground system, and probably also for the below-ground system. We conclude that scale insects have the potential to function as keystone species in these forests.     

Competition for honeydew between two social wasps in South Island beech forests,New Zealand

Summary Honeydew is a sugary secretion of beech scale insects (Ultracoelostoma spp.). Two introduced species of wasps forage on the sugar droplets in New Zealand beech forests. We hypothesize that competition between them may explain whyVespula germanica has become locally extinct in beech (Nothofagus) forest invaded byV. vulgaris. Changes in behaviour of the two wasp species in response to changes in the honeydew resource were monitored. Foraging and rainfall separately and together reduced the honeydew standing crop. In response to the standing crop decreasing, more wasps were found on honeydew trees, they became less active, spent more time lapping the tree surface, and ingested drops of honeydew at a slower rate.V. vulgaris was more active, and obtained drops and energy at a higher rate thanV. germanica. These behavioural differences may lead to competitive advantages affecting queen size and possibly survival.     

Honeydew standing crop and production over 24 hours in

The standing crop and daily production of honeydew by Ultracoelostoma brittini on Nothofagus solandri: var solandri was measured on 28-29 August 1990 near Oxford, Canterbury. In 64 quadrats of 125 cm², all 740 active individual insects were mapped by their anal threads and honeydew production was recorded every three hours over 24 hours. Mean production of honeydew per insect over 24 hours was 0. 1 69 mul, but ranged from zero (4% of all active insects) to 11.5 mul. Standing crop Peaked just after dawn, and production was apparently higher at night. Removing drops every three hours and covering the quadrats to exclude animals had no significant effect on honeydew production. The greatest variation was between the 16 trees. Ultracoelostoma densities were higher on trees with higher daily honeydew production per insect. The honeydew production per unit area over 24 hours represented 3.2 to 23.0 times the standing crop, depending on what time of day the latter was measured; for the daylight samples, production was 11.5 times the mean standing crop.     

An episodic model of honeydew production in scale insects

Honeydew produced by sooty beech scale insects (Ultracoelostoma spp., Homoptera: Coelostomidiidae) is a keystone ecological process in New Zealand beech (Nothofagus spp., Nothofagaceae) forest. This work puts forward a model of honeydew production based on individual insects that presumes feeding and excretion are episodic processes driven by the insect rather than the passive processes that were previously assumed. The model is parameterized using existing data and then compared to an independent pre‐existing dataset. The model suggests that over a 12‐h period, on average the insects suck sap for 2 h, and excrete waste sap for 12 min. Resource uptake by the insects appears to be limited by the time required to process the sap, consistent with the observed relationship between honeydew production rates and ambient temperature. This implies that insect feeding rates may be ultimately limited by the low nitrogen content of phloem sap.     

Separating host-tree and environmental determinants of honeydew production by Ultracoelostoma scale insects in a Nothofagus forest

Abstract 1. Sugar‐rich honeydew excreted (‘produced’) by insects feeding on phloem sap is a key energy flow in a range of temperate and tropical ecosystems. The present study measured honeydew produced by Ultracoelostoma sp. (Homoptera: Coelostomidiidae) scale insects feeding on Nothofagus solandri var. solandri (Hook f.) Oerst. trees in a temperate evergreen forest in New Zealand. Simultaneous measurements of environmental variables and canopy photosynthesis were conducted to allow separation of host‐tree and environmental determinants of honeydew production. These relationships were further examined in experiments where canopy photosynthesis was manipulated by shading or plant nitrogen levels increased by foliar spray. 2. Rates of honeydew production varied nine‐fold from a maximum (± 1 SE) of 64.4 ± 15.2 mg dry mass m⁻² bark h⁻¹ in early summer (December) to a minimum of 7.4 ± 4.2 mg m⁻² h⁻¹ in winter (August). Rates of production measured 1.4 m from the base of the trees’ stems varied significantly with stem diameter, and were higher on medium‐sized (18 cm diameter) than small or large stems. 3. Rates of production were significantly related to environmental conditions over the hours preceding measurement (air temperature and air saturation deficit averaged over the preceding 24 and 12 h respectively). There was no evidence that rates of production were directly related to short‐term changes in the supply of carbohydrates from the canopy (either when compared with measurements of unmanipulated photosynthetic rate, or after sugar levels were manipulated by shading 80% of host‐trees’ leaf area), or to changes in phloem nitrogen content. 4. The results show that there is no clear effect of host‐tree carbon supply on honeydew production; if production is related to photosynthesis, the effect of this is much less important that the large and significant direct effect of environmental conditions on honeydew production.     

Vertical stratification in the spatial distribution of the beech scale insect (Ultracoelostoma assimile) in Nothofagus tree canopies in New Zealand

Abstract. 1. The degree of infestation by New Zealand sooty beech scale insects (Ultracoelostoma assimile, Homoptera: Margarodidae) varies dramatically among adjacent southern beech trees (Nothofagus spp., Fagaceae), but has previously been assumed to be uniformly or randomly distributed within individual host trees. In this study, a full‐census survey was conducted from ground level to canopy level on 14 naturally occurring, canopy‐dominant red beech (Nothofagus fusca) trees (size range 38.7–107.6 cm diameter at breast height) to determine the degree of within‐tree heterogeneity in herbivore density. 2. The within‐tree distribution of the sooty beech scale was vertically stratified and highly heterogeneous, with the greatest densities occurring on bark surfaces in the canopy rather than on the trunk, and on the lower rather than upper sides of the branches. The spatial distribution was strongly negatively correlated with trunk and branch diameter, and increasing bark thickness (as a function of diameter) provides a plausible explanation for differences in the establishment and population density of sooty beech scale insects with trunk and branch size. Furthermore, there was a significant change in the spatial distribution of scale insect populations on trunks and branches of trees of increasing diameter at breast height. This indicates a strong temporal component to the spatial dynamics of the sooty beech scale insect driven by changing host phenology. Future studies on phytophagous insects infesting large host trees need to consider more explicitly changes in population dynamics through space and time. 3. Because of the high degree of within‐tree heterogeneity in population density, the total population size of scale insects on an individual tree could not be predicted from any measure of population density low on the trunk. However, the dry weight biomass of sooty mould fungi growing on the ground beneath infested trees was a remarkably accurate predictor of the total population size of scale insects. The use of sooty mould fungi as a relative measure of population size could be incorporated into studies of other honeydew‐producing hemipterans, since the growth of sooty mould is a distinctive feature synonymous with high concentrations of honeydew production worldwide.     

Seasonal variation in the honeydew, invertebrate, fruit and nectar resource for bellbirds in a New Zealand mountain beech forest

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. Invertebrates were available all year and represented 89% of the available food energy. Only 16% of the invertebrate resource was on beech foliage, and beech trunks with honeydew had 60% more invertebrate energy than trunks without honeydew. The energy value of honeydew at Craigieburn (0.9% of the total) was much lower than at lower altitude sites. The relative rankings of honeydew standing crops on 25 permanently marked trees were very constant. On an annual basis mistletoe nectar and fruit made up 6.3% and 4.9%, respectively, of total food energy, but P. tetrapetala nectar was 46% of available food in early January, and P. tetrapetala fruit was 25% of the total in March. Bellbirds spent less time foraging on invertebrates, and more time on the other foods, than energy values would predict. However, during the Peak of its short flowering season, P. tetrapetala nectar made up 46% of available energy but only 33% of bellbird foraging observations. At this site P. tetrapetala is pollen limited due to insufficient visits from pollinators. This may be because bellbirds require invertebrates for protein, or to feed to nestlings. Therefore the pollination mutualism is faltering, despite high investment in nectar by the plant.     

Invasive wasps,not birds,dominate in a temperate honeydew system

The Avian Convergence Hypothesis states that avian–honeydew associations are likely to develop when biogeographic and/or climatic factors limit the formation of ant–honeydew associations (the dominant association in tropical ecosystems). In this study we examine a honeydew‐influenced forest system in an island archipelago where ant diversity is low but invasive Vespula wasp species (Vespidae) are present. We found honeydew production was highly seasonal, with both standing crop and 24‐h production peaking in summer. When Vespula wasps were abundant (summer and autumn) they preferentially visited infested trees and fed regularly on honeydew droplets on infested branches. Two ant species occasionally fed on honeydew. No other insects or birds were observed feeding on honeydew during the study period. With the exception of Vespula, honeydew does not appear to be a preferred food source in this community, possibly because of the range of other food resources available in surrounding forest, farmland and gardens. The abundance of Vespula wasps at the site may also have disrupted bird–honeydew associations. We suggest the Avian Convergence Hypothesis could be restated to explicitly include both nectar availability and invasive social insects as both are likely to influence bird use of honeydew.     

Honeydew collection by the invasive garden ant Lasius neglectus versus the native ant L. grandis

Honeydew collection performed by the invasive ant Lasius neglectus and by the native ant L. grandis was compared. The invasive ant collected 2.09 kg of honeydew per tree while the native ant collected 0.82 kg. The aphid Lachnus roboris was visited by both ant species. In holm oaks colonized by L. neglectus, aphid abundance tended to increase and its honeydew production increased twofold. The percentage of untended aphids was lower in holm trees occupied by L. neglectus. As tending ants also prey on insects, we estimated the percentage of carried insects. The native ant workers carried more insects than the invasive ant. Both ant species preyed mainly on Psocoptera and the rarely tended aphid, Hoplocallis picta. We conclude that the higher honeydew collection achieved by L. neglectus was the consequence of (1) its greater abundance, which enabled this ant to tend more Lachnus roboris and (2) its greater level of attention towards promoting an increase of honeydew production. Handling editor: Heikki Hokkanen     

Study on Energy of Castanopsis eyrei Community in Wuyi Mountains

Based on the measurement of biomass and productivity, the caloric value of plant samples, the standing crop of energy, net energy production and energy conversing efficiency of Castanopsis eyrei community were determined. There were some differences in caloric values among the fractions of C. eyrei community being highest in that of bark and lowest in that of the microroots. The standing crop of energy in C. eyrei community was 780584.1 kJ ·m-2, in which the standing crop of energy accumulated in the aboveground biomass was 678913.8 kJ · m-2, accounting 86. 98% of the total; that of underground was 101670.3 kJ · m-2, i. e. 13.02%. Net energy production was 26856.2 kJ · m-2 · a-1 for this community in 1992. To the photosynthetic active radiation on the stand, the energy conversing efficiency was 1. 296%.     

Preliminary evidence suggests that beech scale insect honeydew has a negative effect on terrestrial litter decomposition rates in

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. High and low honeydew plots were selected using sooty mould biomass on the forest floor as a surrogate for honeydew throughfall, as sooty mould biomass was shown to be strongly correlated (r = 0.906) with scale insect population size at the Rotoiti site. Contrary to our expectation, terrestrial litter decomposition was significantly lower in high honeydew plots than in low honeydew plots, at both Lakehead and Rotoiti. The presence of introduced wasps (Vespula spp., Hymenoptera: Vespidae) at the Lakehead site did not appear to have any significant effect on litter decomposition rates, despite the fact that wasps are thought to intercept much of the honeydew produced in this forest. Variance in litter decomposition rates between high and low honeydew treatments was predominantly determined by a direct relationship between sooty mould biomass and litter decomposition rate at the scale of individual litter bags. However, the mechanistic explanation for the observed relationship is unclear. Future studies should be directed towards quantifying the functional relationship between honeydew throughfall and growth rates of sooty mould, and their subsequent effects on abiotic conditions, microarthropod community dynamics and microbial activity rates in litter.     

Phloem-sap feeding by animals: problems and solutions

The incidence of phloem sap feeding by animals appears paradoxical. Although phloem sap is nutrient-rich compared with many other plant products and generally lacking in toxins and feeding deterrents, it is consumed as the dominant or sole diet by a very restricted range of animals, exclusively insects of the order Hemiptera. These insects display two sets of adaptations. First, linked to the high ratio of non-essential:essential amino acids in phloem sap, these insects contain symbiotic micro-organisms which provide them with essential amino acids. For example, bacteria of the genus Buchnera contribute up to 90% of the essential amino acids required by the pea aphid Acyrthosiphon pisum feeding on Vicia faba. Second, the insect tolerance of the very high sugar content and osmotic pressure of phloem sap is promoted by their possession in the gut of sucrase-transglucosidase activity, which transforms excess ingested sugar into long-chain oligosaccharides voided via honeydew. Various other animals consume phloem sap by proxy, through feeding on the honeydew of phloem-feeding hemipterans. Honeydew is physiologically less extreme than phloem sap, with a higher essential:non-essential amino acid ratio and lower osmotic pressure. Even so, ant species strongly dependent on honeydew as food may benefit from nutrients derived from their symbiotic bacteria Blochmannia.     

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).     

海莲、秋茄两种红树群落能量的研究

 本文应用热值测定,对中国两种典型红树群落,即海南岛的海莲群落及福建九龙江口的秋茄群落样品热值、群落能量现存量、能量固定量以及太阳能转化效率进行了测定和分析．结果表明：(1)红树群落各组分样品之间热值有一定的差异;一般叶、花的热值较高,而根、树皮的热值较低。(2)群落能量现存量海莲群落(1984年1月)高达178,627kcal／m2,秋茄群落为70,547kcal／m2,群落能量在不同组分以及不同高度层次上均有不同的分配比。(3)海莲群落(1983)、秋茄群落(1982)能量年净固定量分别为15,772kcal／m2和10,456kcal/m2,相应地对林地太阳光合有效辐射能的转化效率依次为3.01％和2.01％;红树群落比其他植物群落具有较高的能量固定能力及太阳能转化效率。     

Honeydew composition and its effect on life-history parameters of hyperparasitoids

1. Diets that maximise life span often differ from diets that maximise reproduction. Animals have therefore evolved advanced foraging strategies to acquire optimal nutrition and maximise their fitness. The free-living adult females of parasitoid wasps (Hymenoptera) need to balance their search for hosts to reproduce and for carbohydrate resources to feed. 2. Honeydew, excreted by phloem-feeding insects, presents a widely available carbohydrate source in nature that can benefit natural enemies of honeydew-producing insects. However, the effects of variation in honeydew on organisms in the fourth trophic level, such as hyperparasitoids, are not yet understood. 3. This study examined how five different honeydew types influence longevity and fecundity of four hyperparasitoid taxa. Asaphes spp. (Pteromalidae) and Dendrocerus spp. (Megaspilidae) are secondary parasitoids of aphid parasitoids and are thus associated with honeydew-producing insects. Gelis agilis and Acrolyta nens (both Ichneumonidae) are secondary parasitoids of species that do not use honeydew-producing hosts. 4. Most honeydew types had a positive or neutral effect on life span and fecundity of hyperparasitoids compared with controls without honeydew, although negative effects were also found for both aphid hyperparasitoids. Honeydew produced by aphids feeding on sweet pepper plants was most beneficial for all hyperparasitoid taxa, which can partially be explained by the high amount of honeydew, but also by the composition of dietary sugars in these honeydew types. 5. The findings of this study underline the value of aphid honeydew as a carbohydrate resource for fourth-trophic-level organisms, not only those associated with honeydew-producing insects but also ‘interlopers’ without such a natural association.     

Competition between Honey-Bees (

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. In laboratory trials, interference competition was often strong, and many cases of aggression were noted. In the forest, there was invariably enough room on the trees for bees and wasps to feed while rarely encountering one another. Over the whole year, environmental variables (especially low temperatures and rain), were found to constrain honey bee foraging to a greater degree than competition with wasps. Because the competition that did occur was primarily exploitation competition, reciprocal effects were likely to be felt. At Coopers Creek, bees may be reducing wasp densities, compared with the situation in Nelson—Marlborough where commercial hives are scarce. It may be possible to reduce wasp densities locally by increasing the number of bee hives in an area.     

Wood decomposition in an abandoned beech and oak coppiced woodland in SE England

The rate of litter decomposition is often expressed as a constant decay rate (k; g g⁻¹ yr⁻¹) or as the time required for a certain percentage (often 95% and estimated as 3/k) of it to decompose (termed turnover time). Estimates of k may be obtained by determining the weight loss of litter in the field and also by assuming a steady state and obtaining the ratio of litter input: standing crop. Both methods were used to estimate decay rate and turnover times for beech and oak branches and twigs decomposing on the forest floor and these were critically evaluated.
Considerable variation, ranging between 1.8–144.5 yr, was found between the 95% turnover time estimates of various size components of the two species, obtained from woodfall and standing crop data. Likewise variation in decay rate of 2–2.5 cm diameter beech branches, estimated from field experiments, was large both between and within groups of branches categorised according to initial state of decay and presence or absence of bark. The mean annual decay rate for the various categories ranged between k = 0.165-0.452 g g⁻¹yr⁻¹. Branches without bark generally decomposed more slowly than those with bark. Beech twig (<0.5 cm diameter) decomposition rates, from field experiments, ranged between k = 0.149-0.220 g g⁻¹yr⁻¹ and variation was relatively low compared with that of branches. No significant differences (P<0.05)were detected between twig decomposition rates obtained from experiments initiated at different seasons although there was a slight decline in decay rate in winter months. Twig and branch decomposition rates fell within the range found in the few other comparable studies.     

Age-specific patterns in honeydew production and honeydew composition in the aphid Metopeurum fuscoviride: implications for ant-attendance

The intensity of the mutualistic relationship between aphids and ants depends mainly on the composition and amount of honeydew. We used the model system Tanacetum vulgare-Metopeurum fuscoviride to study age-related differences in honeydew production and composition and its effect on the mutualism between M. fuscoviride and the ant Lasius niger. First and second instar larvae of M. fuscoviride produced only half of the amount of honeydew as older larvae or adults. There were, however, no differences between age classes in the total honeydew sugar concentration, which averaged approx. 80 μg sugar/μl honeydew. Honeydew sugar composition also did not differ between age classes, and melezitose was the dominant sugar (59% in all classes). The amino acid concentration, by contrast, increased significantly with aphid age, reaching 22.6 nmol per μl honeydew in adult M. fuscoviride. This increase was mainly caused by asparagine and glutamine, while there were no differences in the concentrations of the five other regularly detected amino acids and cystine, respectively. The intensity of ant-attendance was significantly lower in colonies of first and second instar larvae than in colonies of older age classes. Ant-attendance correlated with the amount of honeydew produced, and not with the total amino acid concentration.     

A simple gravimetric technique for estimating honeydew or nectar production

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. A factor was derived to convert gravimetric refractometer readings (g sucrose 100 g^-1 solution) to volumetric carbohydrate concentration (g carbohydrate 100 ml^-1 solution) for the simulated honeydew solutions. There was no difference in the ratio of measured-to-expected carbohydrate mass between the two techniques, showing that the quick, easy, and accurate filter-paper method is appropriate for measuring carbohydrate-rich solutions.     

Soil Base Saturation Combines with Beech Bark Disease to Influence Composition and Structure of Sugar Maple-Beech Forests in an Acid Rain-Impacted Region

Sugar maple, an abundant and highly valued tree species in eastern North America, has experienced decline from soil calcium (Ca) depletion by acidic deposition, while beech, which often coexists with sugar maple, has been afflicted with beech bark disease (BBD) over the same period. To investigate how variations in soil base saturation combine with effects of BBD in influencing stand composition and structure, measurements of soils, canopy, subcanopy, and seedlings were taken in 21 watersheds in the Adirondack region of NY (USA), where sugar maple and beech were the predominant canopy species and base saturation of the upper B horizon ranged from 4.4 to 67%. The base saturation value corresponding to the threshold for Al mobilization (16.8%) helped to define the species composition of canopy trees and seedlings. Canopy vigor and diameter at breast height (DBH) were positively correlated (P < 0.05) with base saturation for sugar maple, but unrelated for beech. However, beech occupied lower canopy positions than sugar maple, and as base saturation increased, the average canopy position of beech decreased relative to sugar maple (P < 0.10). In low-base saturation soils, soil-Ca depletion and BBD may have created opportunities for gap-exploiting species such as red maple and black cherry, whereas in high-base saturation soils, sugar maple dominated the canopy. Where soils were beginning to recover from acidic deposition effects, sugar maple DBH and basal area increased progressively from 2000 to 2015, whereas for beech, average DBH did not change and basal area did not increase after 2010.