Organic versus conventional management in an apple orchard: effects of fertilization and tree-row management on ground-dwelling predaceous arthropods

1 Organic and conventional management of apple orchards may have a different effect on arthropod communities.
2 We conducted a 3-year study to assess the effect of two strategies of fertilizer treatment (organic versus chemical) and three tree-row management systems (straw mulching, tillage and herbicide) on activity-density and biodiversity of epigeic predators. Ground beetles (Carabidae), rove beetles (Staphylinidae), ants (Formicidae) and spiders (Araneae) were sampled monthly with pitfall traps in the same apple orchard during 2003, 2004 and 2005.
3 A total of 4978 individuals were collected. Carabids (56.8% of the total catches) were the most abundant taxonomic group, followed by spiders (20.7%), ants (14.8%) and rove beetles (7.7%). Tree-row management had a greater influence on predator catches than fertilizer treatment. Total predator catches were lower under the mulch. Mulching also reduced carabid abundance, but increased staphylinid catches.
4 Tree row management also had a significant effect on biodiversity parameters. Species richness did not significantly differ among treatments for ants, spiders or the total catches, but was higher on herbicide-treated plots for carabids and on mulched plots for staphylinids. Shannon–Wiener's diversity index was significantly greater in the mulched and herbicide treated plots for total predators and carabids. For staphylinids, this index was significantly greater on the mulched plots. Fertilizer application strategy only influenced the species richness of rove beetles, which was greater in the chemically-treated plots.
5 The results showed that a change from conventional to organic fertilizer treatment of apple trees may be performed without differential effects on predator activity-density or biodiversity. However, a change from herbicide treatment to mulching or mechanical weed control may be significant, depending on the taxonomic group.     

Secondary succession, soil formation and development of a diverse community of oribatids and saprophagous soil macro-invertebrates

Investigations into different stages of secondary succession (from a wheat field to a beechwood on Threstone; Northern Germany) demonstrated the formation of a carbon rich top soil in later successional stages. Parallel to changes in plant species and soil formation, there were also changes in species composition and diversity of saprophagous macro-invertebrates (Lumbricidae, Diplopoda, Isopoda) and oribatid mites (Acari: Oribatida). Diversity of diplopod and isopod species increased after cessation of cultivation, but in a late successional stage (ca 50 y-old fallow, ash-dominated wood) species number of diplopods and isopods declined strongly. In comparison with the other soil invertebrate groups, species composition of earthworms among the sites was more similar. Accumulation of soil C was assumed to be related to wood formation and occurrence of woody debris and recalcitrant leaf litter of beech trees. Incorporation of recalcitrant litter materials by earthworm species living in the upper mineral soil presumably contributed significantly to accumulation of soil C. Accumulation of soil C was accompanied by the development of an oribatid mite community rich in species. In early successional stages oribatids predominantly colonized the litter layer, while most oribatid mites of the beechwood inhabited the upper mineral soil. Maximum diversity of oribatid mites in the beechwood is assumed to be related to instability of the mineral soil caused by earthworm activity. Changes in species composition and diversity are discussed considering succession theory. Even soil invertebrates of similar trophic groups appear to respond very differently to successional changes. It is concluded that conservation strategies to maintain high diversity of soil invertebrates are most likely to be successful if a wide range of habitats of different successional stages is included.     

Belowground biodiversity in a Mediterranean landscape: relationships between saprophagous macroarthropod communities and vegetation structure

Millipedes and woodlice were sampled at 27 sites in a mosaic landscape in order to establish the extent to which the macroarthropod community changed with different plant formations. Multivariate analyses conducted on abundance data for ten species revealed four main types of macroarthropod communities. This classification was highly correlated with vegetation structure and particularly the degree of openness of the sites. Communities dominated by Ommatoiulus rutilans (Julidae) occurred in open grassland; those dominated by Glomeris marginata (Glomeridae) plus Porcellio gallicus (Porcellionidae) were found at the least open sites, with a high oak cover; communities with a high proportion of the endemic glomerid Glomeris annulata occurred in semi-open sites with a substantial cover of shrubs. Species diversity was significantly higher at the semi-open sites, this being interpreted as an edge effect. Population density and biomass were lower at wooded sites. In the context of a regional trend towards woodland expansion, the results are discussed from the viewpoint of conserving the pool of millipede and woodlouse species and of maintaining the abundance of saprophagous macroarthropods in the region's ecosystems.     

Aquatic Terrestrial Linkages Along a Braided-River: Riparian Arthropods Feeding on Aquatic Insects

Rivers can provide important sources of energy for riparian biota. Stable isotope analysis (δ¹³C, δ¹⁵N) together with linear mixing models, were used to quantify the importance of aquatic insects as a food source for a riparian arthropod assemblage inhabiting the shore of the braided Tagliamento River (NE Italy). Proportional aquatic prey contributions to riparian arthropod diets differed considerable among taxa. Carabid beetles of the genus Bembidion and Nebria picicornis fed entirely on aquatic insects. Aquatic insects made up 80% of the diet of the dominant staphylinid beetle Paederidus rubrothoracicus. The diets of the dominant lycosid spiders Arctosa cinerea and Pardosa wagleri consisted of 56 and 48% aquatic insects, respectively. In contrast, the ant Manica rubida fed mainly on terrestrial sources. The proportion of aquatic insects in the diet of lycosid spiders changed seasonally, being related to the seasonal abundance of lycosid spiders along the stream edge. The degree of spatial and seasonal aggregation of riparian arthropods at the river edge coincided with their proportional use of aquatic subsidies. The results suggest that predation by riparian arthropods is a quantitatively important process in the transfer of aquatic secondary production to the riparian food web.     

Winter ecology of the cabbage aphid Brevicoryne brassicae (L.) (Homo., Aphididae) and its parasitoid Diaeretiella rapae (McIntosh) (Hym., Braconidae: Aphidiidae)

Abstract:  Flower strips near crops may stimulate natural enemies by the provision of nectar and hibernation sites. However, these habitats may also be beneficial for potential pest species. We investigated the dynamics of the cabbage aphid Brevicoryne brassicae (L.) (Homo., Aphididae) and its primary parasitoid Diaeretiella rapae (McIntosh) (Hym., Braconidae) in brussels sprout fields and adjoining flower plots in winter. A wide variety of 14 plant species were included in the study, each established as monoculture plots. Brussels sprout fields and flower plots were established at two sites. One site was located in an open agricultural landscape, the other in a landscape dominated by mixed forest. Brevicoryne brassicae and D. rapae were found on brussels sprout plants but not in the flower plots. Brevicoryne brassicae was initially more abundant in the open landscape, but as their densities declined rapidly in time, no living aphids were recovered at both sites by February. The density of aphids parasitized by D. rapae showed a similar trend, but densities of eight mummies per brussels sprout plant were still present by the end of February. These findings suggest that (i) flower species under investigation do not function as sources of B. brassicae and (ii) brussels sprout plants that are not harvested may not only harbour D. rapae populations that may sustain biological control, but are also likely to act as sources of B. brassicae infestation.     

Identifying multiscale habitat factors influencing koala (Phascolarctos cinereus) occurrence and management in Ballarat, Victoria, Australia

Summary   Modelling for the conservation of koala ( Phascolarctos cinereus ) populations has primarily focused on natural habitat variables (e.g. tree species, soil types and soil moisture). Until recently, limited consideration has been given to modelling the effects of the landscape context (e.g. habitat area, habitat configuration and roads). Yet, the combined influence of natural habitats and anthropogenic impacts at multiple spatial scales are likely to be important determinants of where koala populations occur and remain viable in human-modified landscapes. The study tested the importance of multiscale habitat variables on koala occurrence in Ballarat, Victoria, Australia. The models focused at three spatial scales: site ( <  1 ha), patch (1–100 ha), and landscape (100–1000 s ha). Logistic regression and hierarchical partitioning analyses were used to rank alternative models and key explanatory variables.
The results showed that an increased likelihood of koala presence in fragmented landscapes in the urban–forest interface (as opposed to larger blocks of forest habitat) can best be explained by the positive effects of soil fertility and the presence of preferred koala tree species in these fragmented areas. If koalas are to be effectively conserved in Ballarat, it is critical to (i) protect remaining core areas of high-quality habitat, including regenerating areas; (ii) protect scattered habitat patches which provide connectivity; and (iii) develop and implement habitat restoration programmes to improve habitat connectivity and enhance opportunities for safe koala movement between habitat patches intersected by main roads.