Michelle T. Fountain

Divergent composition but similar function of soil food webs of individual plants: plant species and community effects

Soils are extremely rich in biodiversity, and soil organisms play pivotal roles in supporting terrestrial life, but the role that individual plants and plant communities play in influencing the diversity and functioning of soil food webs remains highly debated. Plants, as primary producers and providers of resources to the soil food web, are of vital importance for the composition, structure, and functioning of soil communities. However, whether natural soil food webs that are completely open to immigration and emigration differ underneath individual plants remains unknown. In a biodiversity restoration experiment we first compared the soil nematode communities of 228 individual plants belonging to eight herbaceous species. We included grass, leguminous, and non-leguminous species. Each individual plant grew intermingled with other species, but all plant species had a different nematode community. Moreover, nematode communities were more similar when plant individuals were growing in the same as compared to different plant communities, and these effects were most apparent for the groups of bacterivorous, carnivorous, and omnivorous nematodes. Subsequently, we analyzed the composition, structure, and functioning of the complete soil food webs of 58 individual plants, belonging to two of the plant species, Lotus corniculatus (Fabaceae) and Plantago lanceolata (Plantaginaceae). We isolated and identified more than 150 taxa/groups of soil organisms. The soil community composition and structure of the entire food webs were influenced both by the species identity of the plant individual and the surrounding plant community. Unexpectedly, plant identity had the strongest effects on decomposing soil organisms, widely believed to be generalist feeders. In contrast, quantitative food web modeling showed that the composition of the plant community influenced nitrogen mineralization under individual plants, but that plant species identity did not affect nitrogen or carbon mineralization or food web stability. Hence, the composition and structure of entire soil food webs vary at the scale of individual plants and are strongly influenced by the species identity of the plant. However, the ecosystem functions these food webs provide are determined by the identity of the entire plant community.

Identifying key knowledge needs for evidence-based conservation of wild insect pollinators: A collaborative cross-sectoral exercise

In response to evidence of insect pollinator declines, organisations in many sectors, including the food and farming industry, are investing in pollinator conservation. They are keen to ensure that their efforts use the best available science. We convened a group of 32 ‘conservation practitioners’ with an active interest in pollinators and 16 insect pollinator scientists. The conservation practitioners include representatives from UK industry (including retail), environmental non‐government organisations and nature conservation agencies. We collaboratively developed a long list of 246 knowledge needs relating to conservation of wild insect pollinators in the UK. We refined and selected the most important knowledge needs, through a three‐stage process of voting and scoring, including discussions of each need at a workshop. We present the top 35 knowledge needs as scored by conservation practitioners or scientists. We find general agreement in priorities identified by these two groups. The priority knowledge needs will structure ongoing work to make science accessible to practitioners, and help to guide future science policy and funding. Understanding the economic benefits of crop pollination, basic pollinator ecology and impacts of pesticides on wild pollinators emerge strongly as priorities, as well as a need to monitor floral resources in the landscape.

Biodiversity of Collembola in urban soils and the use of Folsomia candida to assess soil 'quality'

The effects of metal contamination on natural populations of Collembola in soils from five sites in the Wolverhampton area (West Midlands, England) were examined. Analysis revealed that metal concentrations were elevated above background levels at all sites. One location in particular (Ladymoor, a former smelting site) was highly contaminated with Cd, Cu, Pb and Zn at more than 20 times background levels. Biodiversity indices (Shannon–Weiner, Simpson index, Margalef index, alpha index, species richness, Shaneven (evenness) and Berger–Parker dominance) were calculated. Of these indices, estimates of species richness and evenness were most effective at highlighting the differences between the Collembola communities. Indeed, the highest number of species were found at the most contaminated site, although the Collembola population also had a comparatively low evenness value, with just two species dominating. The number of individuals per species were allocated into geometric classes and plotted against the cumulative number of species as a percentage. At Ladymoor, there were more geometric classes, and the slope of the line was shallower than at the other four sites. This characteristic is a feature of polluted sites, where a few species are dominant and most species are rare. The Ladymoor soil also had a dominance of Isotomurus palustris, and was the only site in which Ceratophysella denticulata was found. Previous studies have shown that these two species are often found in sites subject to high metal contamination. Survival and reproduction of the “standard” test springtail, Folsomia candida (Willem), were determined in a 4 week exposure test to soils from all five sites. Mortality was significantly increased in adults and reproduction significantly lower in the Ladymoor soil in comparison to the other four sites. This study has shown that severe metal contamination can be related to the population structure of Collembola in the field, and performance of F. candida (in soils from such sites) in the laboratory.

Arthropod ecosystem services in apple orchards and their economic benefits

Apple is grown as a long‐term perennial crop and orchards provide relatively stable ecological habitats. Only a small proportion of the diverse fauna of arthropods that can inhabit the orchard ecosystem are important pests, the majority of species being minor pests, beneficial or benign. In this paper, the interacting ecosystem services provided by five contrasting naturally occurring arthropod groups in cool temperate apple orchards are reviewed, and their economic benefits broadly quantified. These are:The roles of bees and other insects in apple pollination increasing yields and fruit quality, the economic value of which may be significantly underestimated. Naturally occurring, pesticide‐resistant phytoseiid predatory mites and their role in regulating phytophagous mites. They eliminate the need for 1–2 acaricide sprays per annum and the risk of acaricide resistance. The earwig Forficula auricularia L. and its role in regulating several important apple pests. There is great variability in populations between orchards for reasons not fully understood. It is estimated that F. auricularia reduces insecticide applications by 2–3 per annum and reduces pest damage. Mutualism between the common black ant Lasius niger (L.) and important pest aphids, the roles of competitors, natural and artificial food sources, and ant exclusion in disrupting mutualism which can foster biocontrol of aphids by generalist predators so greatly reducing the need for sprays. Beneficial epigeic arthropods and their role in predating the soil dwelling life stages of insect pests. These contribute to the control of pest populations although the level of suppression is not consistent depending on several ecological factors.

Apple Pollination: Demand Depends on Variety and Supply Depends on Pollinator Identity

Insect pollination underpins apple production but the extent to which different pollinator guilds supply this service, particularly across different apple varieties, is unknown. Such information is essential if appropriate orchard management practices are to be targeted and proportional to the potential benefits pollinator species may provide. Here we use a novel combination of pollinator effectiveness assays (floral visit effectiveness), orchard field surveys (flower visitation rate) and pollinator dependence manipulations (pollinator exclusion experiments) to quantify the supply of pollination services provided by four different pollinator guilds to the production of four commercial varieties of apple. We show that not all pollinators are equally effective at pollinating apples, with hoverflies being less effective than solitary bees and bumblebees, and the relative abundance of different pollinator guilds visiting apple flowers of different varieties varies significantly. Based on this, the taxa specific economic benefits to UK apple production have been established. The contribution of insect pollinators to the economic output in all varieties was estimated to be £92.1M across the UK, with contributions varying widely across taxa: solitary bees (£51.4M), honeybees (£21.4M), bumblebees (£18.6M) and hoverflies (£0.7M). This research highlights the differences in the economic benefits of four insect pollinator guilds to four major apple varieties in the UK. This information is essential to underpin appropriate investment in pollination services management and provides a model that can be used in other entomolophilous crops to improve our understanding of crop pollination ecology.

Multitrophic effects of nutrient addition in upland grassland

Although the effects of nutrient enhancement on aquatic systems are well documented, the consequences of nutritional supplements on soil food webs are poorly understood, and results of past research examining bottom-up effects are often conflicting. In addition, many studies have failed to separate the effects of nutrient enrichment and the physical effects of adding organic matter. In this field study, we hypothesised that the addition of nitrogen to soil would result in a trophic cascade, through detritivores (Collembola) to predators (spiders), increasing invertebrate numbers and diversity. Nitrogen and lime were added to plots in an upland grassland in a randomised block design. Populations of Collembola and spiders were sampled by means of pitfall traps and identified to species. Seventeen species of Collembola were identified from the nitrogen plus lime (N+L) and control plots. Species assemblage, diversity, richness, evenness and total number were not affected by nutrient additions. However, there was an increase in the number of Isotomidae juveniles and Parisotoma anglicana trapped in the N+L plots. Of the 44 spider species identified, over 80% were Linyphiidae. An effect on species assemblage from the addition of N+L to the plots was observed on two of the four sampling dates (July 2002 and June 2003). The linyphiid, Oedothorax retusus, was the only species significantly affected by the treatments and was more likely to be trapped in the control plots.The increased number of juvenile Collembola, and change in community composition of spiders, were consequences of the bottom-up effect caused by nutrient inputs. However, despite efforts to eliminate the indirect effects of nutrient inputs, a reduction in soil moisture in the N+L plots cannot be eliminated as a cause of the invertebrate population changes observed. Even so, this experiment was not confounded by the physical effects of habitat structure reported in most previous studies. It provides evidence of moderate bottom-up influences of epigeic soil invertebrate food webs and distinguishes between nutrient addition and plant physical structure effects. It also emphasises the importance of understanding the effects of soil management practices on soil biodiversity, which is under increasing pressure from land development and food production.

Integrating pesticides and predatory mites in soft fruit crops

Incorporation of predatory mites (Phytoseiidae) as biological control agents in soft fruit integrated pest management (IPM) programmes requires understanding of the interactions between environment, other organisms and crop management practices. This knowledge is dispersed among commercial online databases and peer reviewed papers and can be contradictory or difficult to access and interpret.The review brings together findings from databases and peer reviewed laboratory, field and semi-field studies of pesticide toxicity and persistence to soft fruit phytoseiid mites and also considers resistance, spray programmes and how these interact with species sensitivity, alternative food availability and plant structure.Predictably, acaricides and insecticides are the most toxic pesticides to phytoseiid mites, but their toxicity varies. Few fungicides are harmful, but data for many is lacking; it is very scarce for herbicides. There is virtually no data on tank mixes of pesticides applied to many soft fruit crops. Persistence of pesticides varies so release times for predatory mites after application range from a few days to several weeks and some of the most toxic active ingredients are not always the most persistent. Phytoseiid species vary in susceptibility to pesticides and in some populations resistance has occurred. Interactions with the environment are more difficult to define, but fungicides, for example, may reduce alternative food items whilst plant architecture may offer phytoseiid mites protection from spray residues.This review provides a timely synopsis to inform future research needs and provides practical guidance to enable better management of predatory mites in soft fruit crops.

Development and validation of a model forecasting the phenology of European tarnished plant bug Lygus rugulipennis in the U.K

The European tarnished plant bug Lygus rugulipennis has caused significant economic damage to strawberry production in the U.K. in recent years. Laboratory experiments were conducted to study L. rugulipennis development under fluctuating low temperatures. The results indicated that L. rugulipennis can develop at an appreciable rate at 10 °C. We have developed a model predicting the phenology of L. rugulipennis in the U.K. The model assumes that adults overwinter and uses temperature from the first day of a calendar year to simulate pest development. The model was validated against field observations of L. rugulipennis population dynamics monitored under both open‐field and protected conditions on weeds and strawberry plants. Predicted L. rugulipennis population patterns from the model agreed well with the observed data. The L. rugulipennis model can be used in practice to enable growers to identify the timing of the first generation of L. rugulipennis adult dispersal into strawberry, or other crops, from weeds. The model will also assist growers with the timing of the deployment of pheromone traps and interpreting the importance of trap catches. This will allow growers to better time and target applications of insecticides against damaging life stages of the pest.

Bumblebee olfactory learning affected by task allocation but not by a trypanosome parasite

Parasites can induce behavioural changes in their host organisms. Several parasite species are known to infect bumblebees, an important group of pollinators. Task allocation within bumblebee colonies can also cause differences in behaviour. Thus, task allocation may lead to context-dependent impacts of parasites on host behaviour. This study uses Bombus terrestris and its gut trypanosome Crithidia bombi, to investigate the effects of parasitism, task allocation (foraging or nest-work) and their interactions, on olfactory learning. Prior to undergoing the olfactory learning task, bees were orally infected with a field-realistic dose of C. bombi, and observed to determine task allocation. Parasitism did not significantly affect olfactory learning, but task allocation did, with foragers being significantly more likely to learn than nest bees. There was no significant interaction between parasitism and task. These results suggest that C. bombi is unlikely to affect pollination services via changes in olfactory learning of its host if bees are under no environmental or nutritional stress. However, wild and commercial colonies are likely to face such stressors. Future studies in the field are needed to extrapolate our results to real world effects.

The evaluation of extraction techniques for Tetranychus urticae (Acari: Tetranychidae) from apple ( Malus domestica ) and cherry ( Prunus avium ) leaves

Tetranychus urticae is a widespread polyphagous mite, found on a variety of fruit crops. Tetranychus urticae feeds on the underside of the leaves perforating plant cells and sucking the cell contents. Foliar damage and excess webbing produced by T. urticae can reduce fruit yield. Assessments of T. urticae populations while small provide reliable and accurate ways of targeting control strategies and recording their efficacy against T. urticae. The aim of this study was to evaluate four methods for extracting low levels of T. urticae from leaf samples, representative of developing infestations. These methods were compared to directly counting of mites on leaves under a dissecting microscope. These methods were ethanol washing, a modified paraffin/ethanol meniscus technique, Tullgren funnel extraction and the Henderson and McBurnie mite brushing machine with consideration to: accuracy, precision and simplicity. In addition, two physically different leaf morphologies were compared; Prunus leaves which are glabrous with Malus leaves which are setaceous. Ethanol extraction consistently yielded the highest numbers of mites and was the most rapid method for recovering T. urticae from leaf samples, irrespective of leaf structure. In addition the samples could be processed and stored before final counting. The advantages and disadvantages of each method are discussed in detail.