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Aspergillus nidulans produces sterigmatocystin, a secondary metabolite mycotoxin, for the protection of its reproductive structures. Previous studies on grazing behavior of fungivore arthropods, regulation of sexual development, and secondary metabolite biosynthesis have revealed the association of sterigmatocystin biosynthesis with sexual reproduction, but the spatial distribution of sterigmatocystin producing hyphae within the colony has never been investigated. In this work, we aimed to locate the site of sterigmatocystin production within the colony by employing a yCFP reporter system. We demonstrated that the stcO promoter is active only in vegetative hyphae that surround groups of hülle cells and the activity decreases and eventually ceases as the distance between the hypha and the hülle cells increases. This phenomenon indicates that the vegetative mycelium might consist of morphologically uniform, but functionally different hyphae.

Both top-down (grazing) and bottom-up (resource availability) forces can determine the strength of priority effects, or the effects of species arrival history on the structure and function of ecological communities, but their combined influences remain unresolved. To test for such influences, we assembled experimental communities of wood-decomposing fungi using a factorial manipulation of fungivore (Folsomia candida) presence, nitrogen availability, and fungal assembly history. We found interactive effects of all three factors on fungal species composition and wood decomposition 1 year after the fungi were introduced. The strength of priority effects on community structure was affected primarily by nitrogen availability, whereas the strength of priority effects on decomposition rate was interactively regulated by nitrogen and fungivores. These results demonstrate that top-down and bottom-up forces jointly determine how strongly assembly history affects community structure and function.

The mushroom phorid fly, Megaselia halterata (Wood) (Diptera: Phoridae), is a key pest in mushroom farming in most parts of the world. Studies on the mushroom phorid fly have focused on its life history within mushroom growing houses, but little is known about the fly's activity outside mushroom growing houses. In this study, daily activity and distribution of adult M. halterata in the areas surrounding mushroom growing houses was studied using yellow sticky traps. Results suggest that M. halterata focuses its flight activity over turf areas rather than windbreaks and spent compost piles, possibly for mating purposes. Our study found no evidence of M. halterata breeding in turf areas surrounding mushroom growing houses. In addition, flight activity is highest in the afternoon until midnight at higher temperatures, yet at lower temperatures activity ceases after sunset. Establishing temperature and daylight thresholds for M. halterata flight activity may be useful in developing integrated pest management (IPM) tactics for this species. The most successful IPM tool that mushroom growers use at present is fly exclusion. Exclusion can be improved by focusing farm operations around temperature and daylight thresholds when fly activity is at its lowest.

1. Aggregative behaviour in fungivorous soil arthropods is widespread; its adaptive value, however, is largely unknown. In this study, the spatial foraging behaviour of a collembolan, Folsomia candida, and the fitness consequences of feeding at different densities on the filamentous fungus Aspergillus nidulans were investigated. The effect of two fungal strains were compared; a wild-type (wt) and a transgenic strain that lacks the ability to express the global secondary metabolite regulator LaeA (ΔlaeA). 2. In laboratory foraging tests, F. candida exhibited aggregated distributions of individuals across four distinct fungal colonies that were arranged in short distances from each other. By quantifying the extent of the feeding damage at each single colony, a more evenly distributed feeding activity was found among wt colonies than among chemical-deficient colonies. 3. In a fitness experiment, where collembolans at different densities were restricted to feed on single A. nidulans colonies, mean growth rate of F. candida was positively related to density on the wt A. nidulans strain, but negatively related to density on the chemical-deficient strain. 4. Depending on the fungus' ability to express secondary chemicals and availability of fungal food sources, F. candida may employ different foraging strategies: (i) avoidance of prolonged feeding on single colonies in a rich habitat (travel costs low), and (ii) intensified group feeding on single colonies in a resource-limited habitat (travel costs high). It was hypothesised that flexibility in fungivore foraging behaviour (clumping vs. spreading feeding activity) is adaptive because it allows avoidance/overcoming induced fungal chemical defence.

Orchid mycorrhiza probably affects about 25 000 plant species and thus roughly one tenth of all higher plants. Histologically, this symbiosis resembles other kinds of endomycorrhiza, the fungal hyphae growing within living plant cells. Considerable evidence, however, suggests that it is not a two-way exchange relationship and thus not potentially mutualistic, such as the wide-spread endomycorrhiza between plants and Glomalean fungi, known as arbuscular mycorrhiza. During the achlorophyllous seedling stage orchids are obligately dependent on the fungi; some species remain so through life, while others establish photosynthesis but to varying degrees remain facultatively dependent of / responsive to fungal infection as adults. None of the fungi involved are so far known to depend on the symbiosis with orchids. Transfer of organic carbon compounds from hyphae to the orchid has been demonstrated repeatedly, but it is not clear to what extent this takes place during a biotrophic phase while the intracellular hyphae remain intact, or during the subsequent extensive degradation of the hyphal coils. The advantage of viewing orchid mycorrhiza basically as a unilateral mycophagous relationship, in spite of hypothetical beneficial spin-offs to the mycobiont, is that it provides a conceptual framework similar to that of other parasitic or fungivore relationships; mechanisms known in such relationships could be searched for in future studies of the orchid-fungus symbiosis. These could include mechanisms for recognition, attraction and selection of fungi, physiological regulation of internal hyphal growth, breakdown, and material transfer, nutritional consequences of the plant's preference(s) and trophic changes, fungal avoidance mechanisms, and consequences at population and ecosystem levels. A whole range of possible life strategies becomes apparent that could support divergent evolution and lead to the proliferation of species that has indeed occurred in the orchid family. We outline some of the possible physiological mechanisms and ecological implications of this approach.

Epichloe spp. (Ascomycetes: Clavicipitaceae) are endophytic fungii of Pooid grasses that cause choke disease, the suppression of seed production. They also host Botanophila spp. (Diptera: Anthomyiidae), the larvae of which feed on the fungus. Studies on Epichloe elymi on wild grasses indicate that the flies transfer spermatia between Epichloe mating types, thereby affecting cross-fertilization, suggesting that the fungus-fly interaction reflects obligatory mutualism. Epichloe typhina, inadvertently introduced into western USA, was first detected in cultivated Dactylis glomerata L. fields in 1996. It spread rapidly, raising concerns about impacts on seed production. The present study was conducted to address questions pertaining to the occurrence and nature of the fungus-fly interaction in the new habitat of E. typhina. The first report of an endemic Botanophila species associated with E. typhina in Oregon is presented here. Surveys of D. glomerata fields indicated no correlation between fly abundance and fungal fertilization. In one field, no fly eggs or larvae were detected, but fertilized stromata were universally present. The fly was established in the remaining 12 fields surveyed, but while the number of stromata with fly larvae ranged from 6 to 98%, stromata development was uniform. Up to 10 larvae were present on a stroma, and these consumed >90% of the perithecia. Comparisons of pupal weights indicated that the fungal resource was not limiting, even at high larval densities. An exclusion study in a D. glomerata field also indicated that E. typhina fertilization occurred without the fly. In Oregon, the fly clearly benefits from the association with the fungus, but there is no evidence of benefit to the fungus. Thus if obligatory mutualism in the fungus-fly relationship described from the midwestern USA is the norm, our studies suggest a shift in the interaction to one of simple foraging on the fungus by fly larvae.

The drosophilid fauna in Australia offers an important study system for evolutionary studies. Larval hosts are unknown for most species, however, and this imposes serious limits to understanding their ecological context. The present paper reports the first systematic, large-scale field survey of potential larval hosts to be conducted, in order to obtain an overview of the host utilisation patterns of Australian drosophilids. Potential hosts (mostly fruit and fungi) were collected from different vegetation types in northern and eastern Australia. Host data were obtained for 81 drosophilid species from 17 genera (or 28% of the known Fauna). Most genera were restricted to either fruit or fungi, although Scaptodrosophila spp. and Drosophila spp. were recorded from fruit, fungi, flowers and compost, and Drosophila spp. also emerged from the parasitic plant Balanophora fungosa. There was no evidence that use of either fruit or fungi was correlated to host phylogeny. Drosophilids emerged from hosts collected from all sampled vegetation types (rainforest, open forest, heath and domestic environments). Vegetation type influenced drosophilid diversity, both by affecting host availability and because some drosophilid species apparently restricted their search for hosts to particular vegetation types.

Summary 1. This paper describes the structure of the insect communities inhabiting two old-growth forest specialist bracket fungi, Amylocystis lapponica and Fomitopsis rosea. To study the consequences of old-growth forest fragmentation on community structure, non-fragmented and fragmented forest areas in eastern and southern Finland were compared. 2. Both fungal species are inhabited by more than 50 insect species. The most abundant species in the A. lapponica community is a melandryid beetle Hallomenus sp., and in the F. rosea community a tineid moth Agnathosia mendicella. The occurrence of several nationally or globally rare species underscores the importance of specific insect microhabitats, such as the specialist fungi A. lapponica and F. rosea, for the persistence of specialised insects in old-growth forests. 3. The species composition in both fungal species differs greatly from each other. The food webs are characterised by one numerically dominant host-specific primary fungivore, which implies that fungivorous species inhabiting bracket fungi may be more specialised on a particular host than is generally thought. 4. The community structure was the same in the highly fragmented and in the non-fragmented study areas, probably because fragmentation has occurred relatively recently.

The authors used a refined microcosm technique to investigate the toxicity of copper, cadmium, malathion, and the polychlorinated biphenyl, to trophic groups of soil nematodes and to the microarthropod community. Comparisons of changes in nematode abundance in control soils through time indicated that day 7 was the most appropriate time to sample the microcosms after chemical application. Nematode abundance was reduced after exposure to copper at 100 {micro}g/g, with fungivore, bacterivore, and omnivore-predator nematodes being the most sensitive groups. Cadmium did not affect the nematode or microarthropod communities. Microarthropods were far more sensitive to malathion than were nematodes, and total microarthropod abundance was lower than controls at 400 {micro}g/g. Prostigmatid mites and other arthropods were the most affected groups. PCB also had a greater negative impact on microarthropods than on nematodes. Total microarthropod abundance declined at 2,500 {micro}g/g, with prostigmatid and oribatid mites exhibiting the highest susceptibility. Strong differential sensitivity between nematode and microarthropod communities indicates that both groups should be examined to fully evaluate the biological impact of chemicals on soils. The authors conclude that microcosms with field-collected soil microfaunal communities offer high resolution of the ecotoxicologic effects of chemicals in complex soil systems.

A microcosm technique is presented that uses community and trophic-level analysis of soil nematodes and microarthropods to determine the effects of chemicals on soil systems. Forest soil was treated with either copper (0, 100, 200, 400, and 600 mg g−1), p-nitrophenol (0, 20, 40, 80, and 160 mg g−1), or trinitrotoluene (0, 25, 50, 100, and 200 mg g−1). Nematodes were sorted into bacterivore, fungivore, herbivore, and omnivore-predator trophic groups, and a hatchling category. Microarthropods were sorted to the acarine suborders Prostigmata, Mesostigmata, and Oribatida; the insectan order Collembola; and a miscellaneous group. Omnivore-predator nematodes and mesostigmatid and oribatid mites were the groups most sensitive to copper and were significantly reduced at levels as low as 100 mg g−1 copper. Total nematode and microarthropod numbers declined above 200 mg g−1 copper. Trophic structure analysis suggested that high sensitivity of nematode predators to intermediate levels of copper reduced predation on herbivore nematodes and resulted in greater numbers of nematodes compared to controls. p-Nitrophenol was very toxic to the nematode community, and all trophic groups were significantly reduced above 20 mg g−1. However, there was no effect of p-nitrophenol on microarthropods. Trinitrotoluene had no significant negative effect on total abundance of either group of soil fauna, but oribatids were significantly reduced at 200 mg g−1. Our results demonstrated that soil nematodes and microarthropods were sensitive indicators of environmental contaminants and that trophic-structure and community analysis has the potential to detect more subtle indirect effects of chemicals on soil food-web structure. We conclude that microcosms with field communities of soil microfauna offer high resolution of the ecotoxicological effects of chemicals in complex soil systems.

We conducted field experiments to test the general hypothesis that the com- position of decomposer communities and their trophic interactions can influence patterns of plant litter decomposition and nitrogen dynamics in ecosystems. Conventional (CT) and no-tillage (NT) agroecosystems were used to test this idea because of their structural sim- plicity and known differences in their functional properties. Biocides were applied to ex- perimentally exclude bacteria, saprophytic fungi, and microarthropods in field exclosures. Abundances of decomposer organisms (bacteria, fungi, protozoa, nematodes, microar- thropods), decomposition rates, and nitrogen fluxes were quantified in surface and buried litterbags (Secale cereale litter) placed in both NT and CT systems. Measurements of in situ soil respiration rates were made concurrently. The abundance and biomass of all microbial and faunal groups were greater on buried than surface litter. The mesofauna contributed more to the total heterotrophic C in buried litter from CT (6-22%) than in surface litter from NT (0.4-1/1%). Buried litter decay rates (1.4-1.7%/d) were -2.5 times faster than rates for surface litter (0.5-O.7%/d). Ratios of fungal to bacterial biomass and fungivore to bacterivore biomass on NT surface litter generally increased over the study period resulting in ratios that were 2.7 and 2.2 times greater, respectively, than those of CT buried litter by the end of the summer. The exclusion experiments showed that fungi had a somewhat greater influence on the decomposition of surface litter from NT while bacteria were more important in the de- composition of buried litter from CT. The fungicide and bactericide reduced decomposition rates of NT surface litter by 36 and 25% of controls, respectively, while in CT buried litter they were reduced by 21 and 35% of controls, respectively. Microarthropods were more important in mobilizing surface litter nitrogen by grazing on fungi than in contributing to litter mass loss. Where fungivorous microarthropods were experimentally excluded, there was less than a 5% reduction in mass loss from litter of both NT and CT, but fungi- fungivore interactions were important in regulating litter N dynamics in NT surface litter. As fungal densities increased following the exclusion of microarthropods on NT surface litter, there was 25% greater N retention as compared to the control after 56 d of decay. Saprophytic fungi were responsible for as much as 86% of the net N immobilized (1.81 g /m2) in surface litter by the end of the study when densities of fungivorous microarthropods were low. Although bacteria were important in regulating buried litter decomposition rates and the population dynamics of bacterivorous fauna, their influence on buried litter N dynamics remains less clear. The larger microbial biomass and greater contribution of a bacterivorous fauna on buried litter is consistent with the greater carbon losses and lower carbon assimilation in CT than NT agroecosystems. In summary, our results suggest that litter placement can strongly influence the com- position of decomposer communities and that the resulting trophic relationships are im- portant to determining the rates and timing of plant litter decomposition and N dynamics. Furthermore, cross placement studies suggest that the decomposer communities within each tillage system, while not discrete, are adapted to the native litter placements in each.

To date, research on the effects of forest defoliator outbreaks and pesticide applications to suppress these outbreaks on non-target forest arthropods has generally focused on non-target Lepidoptera and has not examined effects on regional diversity. In this study, we assessed the effects of forest defoliation by gypsy moths and application of the microbial pesticide Bacillus thuringiensis var. kurstaki (Btk) to suppress gypsy moth populations on the species richness and (Shannon index) diversity of beetles in Shenandoah National Park, Virginia. In addition, we examined how these disturbances affected overall beetle abundance and abundances within different feeding guilds (herbivore, predator, fungivore, or xylophage). Three years after a gypsy moth outbreak, beetles were sampled four times throughout spring and summer at 15 sites belonging to one of three disturbance histories: undisturbed, defoliated, or sprayed with Btk. Beetles were captured using blacklight traps and then sorted to family and morphos...

Theory predicts that spatial structure can mediate interactions that affect species diversity in a patchy environment. A rarely considered effect of spatial structure on biodiversity is the interplay of spatial habitat arrangement with species interactions at multiple spatial scales. We investigated how spatial habitat arrangement and predation mediate the assembly of the larval communities of fungivorous insects breeding in the oyster mushroom, Pleurotus ostreatus (Jacq. ex Fr.) P.Kumm in a North American woodland. In a two-way factorial design, we varied the spatial arrangement of mushroom clumps (‘clustered', ‘patchy', and ‘uniform'; 3 levels) crossed with predator exclusion (access allowed or not; 2 levels) to study their joint effects on patterns of α, β and γ diversity of the fungivorous insect communities. Partitioning diversity into these three components suggested that neither spatial nor predation treatments significantly affected α, β and γ diversity. We found that an intermediate inter-clump d...

The most common system responses attributed to microfloral grazers (protozoa, nema- todes, microarthropods) in the literature are increased plant growth, increased N uptake by plants, decreased or increased bacterial populations, increased CO2 evolution, increased N and P mineral- ization, and increased substrate utilization. Based on this evidence in the literature, a conceptual model was proposed in which microfloral grazers were considered as separate state variables. To help evaluate the model, the effects of microbivorous nematodes on microbial growth, nutrient cycling, plant growth, and nutrient uptake were examined with reference to activities within and outside of the rhizosphere. Blue grama grass (Bouteloua gracilis) was grown in gnotobiotic microcosms containing sandy loam soil low in inorganic N, with or without chitin amendments as a source of organic N. The soil was inoculated with bacteria (Pseudomonas paucimobilis or P. stutzeri) or fungus (Fusarium oxysporum), with half the bacterial microcosms inoculated with bacterial-feeding nematodes (Pelodera sp. or Ac- robeloides sp.) and half the fungal microcosms inoculated with fungal-feeding nematodes (Aphelenchus avenae). Similar results were obtained from both the unamended and the chitin-amended experiments. Bacteria, fungi, and both trophic groups of nematodes were more abundant in the rhizosphere than in nonrhizosphere soil. All treatments containing nematodes and bacteria had higher bacterial densities than similar treatments without nematodes. Plants growing in soil with bacteria and bacterial-feeding nematodes grew faster and initially took up more N than plants in soil with only bacteria, because of increased N mineralization by bacteria, NH4+-N excretion by nematodes, and greater initial exploi- tation of soil by plant roots. Addition of fungal-feeding nematodes did not increase plant growth or N uptake because these nematodes excreted less NH4+-N than did bacterial-feeding nematode pop- ulations and because the N mineralized by the fungus alone was sufficient for plant growth. Total shoot P was significantly greater in treatments with fungus or Pelodera sp. than in the sterile plant control or treatments with plants plus Pseudomonas stutzeri until the end of the experiment. The additional mineralization that occurs due to the activities of microbial grazers may be sig- nificant for increasing plant growth only when mineralization by microflora alone is insufficient to meet the plants' requirements. However, while the advantage of increased N mineralization by mi- crobial grazers may be short-term, it may occur in many ecosystems in those short periods of ideal conditions when plant growth can occur. Thus, these results support other claims in the literature that microbial grazers may perform important regulatory functions at critical times in the growth of plants.

Soil/litter inhabiting annelids and arthropods were studied for one year in a mesic deciduous woodland, Andersby angsbackar, one of the most northerly areas in Sweden to possess unbroken oak/hazel vegetation. Lumbricidae, Enchytraeidae, Collembola, Acari, Coleoptera, Diptera and Araneae were important faunal groups with regard to abundance, biomass and respiratory metabolism. Annual mean biomass (8 g dw m−2) and respiration (450 kJ m −2 yr−1) of the joint annelid and arthropod community were dominated by lumbricids (76 and 50%, respectively). The biomass and respiration of the annelids and arthropods at Andersby were lower than in some other oak forests in northwestern Europe, probably because of lower soil temperature, lower litter supply and because some lumbricid and diplopod species were at their northern border of distribution. Of the annual respiration, saprovores, fungivores, carnivores and root-feeders contributed 65, 19, 14 and 1.5%, respectively. The saprovore percentage was lower at Andersby than at other mull sites compared, probably as an effect of the northern climate, which might favour microbial saprovory. The fungivore and carnivore percentages were higher, which might be due to the presence of a litter layer throughout the year.