Atmospheric Degradation of Ecologically Important Biogenic Volatiles:Investigating the Ozonolysis of (E)-β-Ocimene, Isomers of α and β-Farnesene, α-Terpinene and 6-Methyl-5-Hepten-2-One, and Their Gas-Phase Products

Biogenic volatile organic compounds (bVOCs), synthesised by plants, are important mediators of ecological interactions that can also undergo a series of reactions in the atmosphere. Ground-level ozone is a secondary pollutant generated through sunlight-driven reactions between nitrogen oxides (NOx) and VOCs. Its levels have increased since the industrial revolution and reactions involving ozone drive many chemical processes in the troposphere. While ozone precursors often originate in urban areas, winds may carry these hundreds of kilometres, causing ozone formation to also occur in less populated rural regions. Under elevated ozone conditions, ozonolysis of bVOCs can result in quantitative and qualitative changes in the gas phase, reducing the concentrations of certain bVOCs and resulting in the formation of other compounds. Such changes can result in disruption of bVOC-mediated behavioural or ecological interactions. Through a series of gas-phase experiments using Gas Chromatography Mass Spectrometry (GC-MS) and Proton Transfer Reaction Mass Spectrometry (PTR-MS), we investigated the products and their yields from the ozonolysis of a range of ubiquitous bVOCs, which were selected because of their importance in mediating ecological interactions such as pollinator and natural enemy attraction and plant-to-plant communication, namely: (E)-β-ocimene, isomers of α and β-farnesene, α-terpinene and 6-methyl-5-hepten-2-one. New products from the ozonolysis of these compounds were identified, and the formation of these compounds is consistent with terpene-ozone oxidation mechanisms. We present the degradation mechanism of our model bVOCs and identify their reaction products. We discuss the potential ecological implications of the degradation of each bVOC and of the formation of reaction products

A review of the factors that influence pesticide residues in pollen and nectar: future research requirements for optimising the estimation of pollinator exposure

In recent years, the impact of Plant Protection Products (PPPs) on insect pollinator decline has stimulated significant amounts of research, as well as political and public interest. PPP residues have been found in various bee-related matrices, resulting in governmental bodies worldwide releasing guidance documents on methods for the assessment of the overall risk of PPPs to different bee species. An essential part of these risk assessments are PPP residues found in pollen and nectar, as they represent a key route of exposure. However, PPP residue values in these matrices exhibit large variations and are not available for many PPPs and crop species combinations, which results in inaccurate estimations and uncertainties in risk evaluation. Additionally, residue studies on pollen and nectar are expensive and practically challenging. An extrapolation between different cropping scenarios and PPPs is not yet justified, as the behaviour of PPPs in pollen and nectar is poorly understood. Therefore, this review aims to contribute to a better knowledge and understanding of the fate of PPP residues in pollen and nectar and to outline knowledge gaps and future research needs. The literature suggests that four primary factors, the crop type, the application method, the physicochemical properties of a compound and the environmental conditions have the greatest influence on PPP residues in pollen and nectar. However, these factors consist of many sub-factors and initial effects may be disguised by different sampling methodologies, impeding their exact characterisation. Moreover, knowledge about these factors is ambiguous and restricted to a few compounds and plant species. We propose that future research should concentrate on identifying relationships and common features amongst various PPP applications and crops, as well as an overall quantification of the described parameters; in order to enable a reliable estimation of PPP residues in pollen, nectar and other bee matrices

The effects of diesel exhaust pollution on floral volatiles and the consequences for honey bee olfaction

There is growing evidence of a substantial decline in pollinators within Europe and North America, most likely caused by multiple factors such as diseases, poor nutrition, habitat loss, insecticides, and environmental pollution. Diesel exhaust could be a contributing factor to this decline, since we found that diesel exhaust rapidly degrades floral volatiles, which honey bees require for flower recognition. In this study, we exposed eight of the most common floral volatiles to diesel exhaust in order to investigate whether it can affect volatile mediated plant-pollinator interaction. Exposure to diesel exhaust altered the blend of common flower volatiles significantly: myrcene was considerably reduced, β-ocimene became undetectable, and β-caryophyllene was transformed into its cis-isomer isocaryophyllene. Proboscis extension response (PER) assays showed that the alterations of the blend reduced the ability of honey bees to recognize it. The chemically reactive nitrogen oxides fraction of diesel exhaust gas was identified as capable of causing degradation of floral volatiles

Evaluating the effects of integrating trees into temperate arable systems on pest control and pollination

Agroforestry systems, which incorporate trees into agricultural land, could contribute to sustainable agricultural intensification as they have been shown to increase land productivity, biodiversity and some regulating ecosystem services. However, the effect of temperate agroforestry systems on pest control and pollination services has not been comprehensively reviewed, despite the importance of these services for sustainable intensification. We review and analyse the available evidence for silvoarable agroforestry systems, following which we propose a predictive framework for future research to explain the observed variation in results, based on ecological theory and evidence from analogous systems. Of the 12 studies included in our meta-analysis of natural enemies and pests, the observed increases in natural enemy abundance (+24%) and decreases in arthropod herbivore/pest abundance (-25%) in silvoarable systems were both significant, but molluscan pests were more abundant in silvoarable systems in the two available studies. Only three studies reported effects on pollinators, but all found higher abundance in silvoarable compared with arable systems. Measures of pest control or pollination service are scarce, but suggest stronger effect sizes. Our framework seeks to establish hypotheses for future research through an interpretation of our findings in the context of the wider literature, including landscape characteristics, silvoarable system design and management, system maturity, trophic interactions and experimental design. Our findings suggest that silvoarable systems can contribute to sustainable intensification by enhancing beneficial invertebrates and suppressing arthropod pests compared with arable, but future research should include measures of pest control and pollination and implications for productivity and economic value

Evaluating a trait-based approach to compare natural enemy and pest communities in agroforestry versus arable systems

Diversified farming systems, for example those that incorporate agroforestry elements, have been proposed as a solution that could maintain and improve multiple ecosystem services. However, habitat diversification in and around arable fields has complex and inconsistent effects on invertebrate crop pests and their natural enemies. This hinders the development of policy recommendations to promote the adoption of such management strategies for the provision of natural pest control services. Here, for the first time we conducted a trait-based approach to investigate the effect of farming system on plant, invertebrate herbivore and invertebrate natural enemy communities. We then evaluated this approach by comparing the results to those generated using a traditional taxonomic approach. At each of three working farms, we sampled within an agroforestry field (a diverse farming system comprising alleys of arable crops separated by tree rows), and within a paired non-diversified area of the farm (arable control field). Each of 96 sample points was sampled between eight and ten times, yielding 393,318 invertebrate specimens from 344 taxonomic groups. Diet specialization or granivory, lack of a pupal stage, and wing traits in invertebrates, along with late flowering, short flowering duration, creeping habit and perenniality in plants, were traits more strongly associated with agroforestry crop alleys than the arable control fields. We hypothesise that this is a result of reduced habitat disturbance and increased habitat complexity in the agroforestry system. Taxonomic richness and diversity were higher in the agroforestry crop alleys compared to the arable control fields, but these effects were stronger at lower trophic levels. However, functional trait diversity of natural enemies was significantly higher in the agroforestry crop alleys than the arable control fields, suggesting an improved level of biocontrol, which was not detected by traditional diversity metrics. Of eight key pest taxa, three were significantly suppressed in the agroforestry system, whilst two were more abundant, compared to the arable control fields. Trait-based approaches can provide a better mechanistic understanding of farming system effects on pests and their natural enemies, therefore we recommend their application and testing in future studies of diversified farming systems

Residue dynamics of a contact and a systemic fungicide in pollen, nectar, and other plant matrices of courgette (Cucurbita pepo L.)

Pollen and nectar can be contaminated with a range of pesticides, including insecticides, fungicides, and herbicides. Since these matrices are important food sources for pollinators and other beneficial insects, their contamination can represent a key route of exposure. However, limited knowledge exists with respect to pesticide residue levels and their dynamics in these matrices for many crops and active ingredients (AIs). We used controlled glasshouse studies to investigate the residue dynamics of a systemic (cyprodinil) and a contact (fludioxonil) fungicide in the floral matrices and other plant parts of courgette/zucchini (Cucurbita pepo L.). We aimed to better understand the processes behind residue accumulation and decline in pollen and nectar. Each AI was applied to plants, either by spraying whole plants or by targeted spraying onto leaves only. Samples of pollen, nectar, anthers, flowers, and leaves were taken on the day of application and each subsequent morning for up to 13 days and analysed for residues using LC-MS/MS. Significant differences in residue levels and dynamics were found between AIs and floral matrices. The present study allowed for the identification of potential routes by which residues translocate between tissues and to link those to the physicochemical properties of each AI, which may facilitate the prediction of residue levels in pollen and nectar. Residues of the contact AI declined more quickly than those of the systemic AI in pollen and nectar. Our results further suggest that the risk of oral exposure for pollinators may be considerably reduced by using contact AIs during the green bud stage of plants, but application of systemic compounds could still result in a low, but continuous long-term exposure for pollinators with limited decline

Concurrent anthropogenic air pollutants enhance recruitment of a specialist parasitoid

Air pollutants, such as nitrogen oxides, emitted in diesel exhaust, and ozone, disrupt interactions between plants, the insect herbivore pests that feed upon them, and natural enemies of those herbivores (e.g., parasitoids). Using eight field-based rings that emit regulated quantities of diesel exhaust and ozone, we investigated how both pollutants, individually and in combination, altered the attraction and parasitism rate of a specialist parasitoid (Diaeretiella rapae) on aphid-infested and un-infested Brassica napus plants. Individual effects of ozone decreased D. rapae abundance and emergence by 37% and 55%, respectively, compared with ambient (control) conditions. When ozone and diesel exhaust were emitted concomitantly, D. rapae abundance and emergence increased by 79% and 181%, respectively, relative to control conditions. This attraction response occurred regardless of whether plants were infested with aphids and was associated with an increase in concentration of aliphatic glucosinolates, especially gluconapin (3-butenyl glucosinolate), within B. napus leaves. Plant defensive responses and their ability to attract natural aphid enemies may be beneficially impacted by pollution exposure. These results demonstrate the importance of incorporating multiple air pollutants when considering the effects of air pollution on plant-insect interactions

Modelling the factors affecting the spatiotemporal distribution of cabbage stem flea beetle (Psylliodes chrysocephala) larvae in winter oilseed rape (Brassica napus) in the UK

BACKGROUND Cabbage stem flea beetle (CSFB; Psylliodes chrysocephala L.) management in oilseed rape (Brassica napus L.) has become an urgent issue in the absence of permitted and effective insecticides. Understanding the meteorological and management factors affecting their population dynamics has become critical to the development of pest management strategies. RESULTS The spatio-temporal changes in CSFB larval populations were assessed both in autumn and spring, in the UK from 2003 to 2017 (a period encompassing pre-and post-neonicotinoid insecticide restriction). After the neonicotinoid ban in 2013, the number of larvae both in autumn and spring increased 10-fold in the UK. When neonicotinoids were available, later sown crops contained fewer larvae than early sown crops, and bigger fields had fewer larvae than smaller fields, whereas after the ban, bigger fields tended to have more larvae than smaller fields. Wet and mild/hot Septembers were related with higher numbers of larvae when neonicotinoids were available and with lower larval numbers after the neonicotinoid ban. Low temperatures in December and January combined with high rainfall were related with high numbers of larvae in spring both before and after the neonicotinoid ban. CONCLUSION This study will help to produce decision support systems that allow future predictions of regional CSFB population changes and will help growers and consultants to adjust their management methods to reduce the risk of high infestations

Weed suppression and tolerance in winter oats

A crops ability to both suppress weed growth and tolerate weed competition is a key consideration when taking an agroecological approach to weed management. Amongst other cereals, oats are widely considered to have superior weed competitiveness yet studies examining competitive ability between oat varieties are rare. We investigated the ability of oats to suppress weeds and yield in the presence of competition from weeds in trials involving five husked and three naked oat varieties at an organic site in the east of England over four trial years (2009-13). We identified a number of key traits that were important for weed suppression including establishment rates, tillering ability, and early Leaf Area Index (LAI) which highlight the importance of rapid early growth rates. Furthermore, taller varieties tended to be more weed tolerant but not necessarily more suppressive. Trade-offs between competitive traits and yield were not found in this study. Crop tillering ability was highlighted as an important trait for selection due to its beneficial effects on weed suppression as well as grain yield and also its high heritability

Rural livelihood diversity and its influence on the ecological intensification potential of smallholder farms in Kenya

Smallholder farmers represent the majority of food producers around the world, yet they are often the most at risk of suffering yield gaps and not achieving their production potential. Ecological Intensification (EI) is a knowledge intensive approach to sustainable agricultural intensification which utilises biodiversity-based ecosystem services to support greater yield and reduce reliance on agrochemical inputs. Despite the potential benefit of EI based practices, uptake by smallholders is not as widespread as it could be. Here we test the hypothesis that application of EI on smallholder farms in Kenya is a viable approach that could be taken in order to enhance food security. Focusing on natural pest control and crop pollination, we used farmer surveys to explore the potential for EI in central Kenya. We identified to what extent farm typology and access to knowledge determine the incentives and barriers facing smallholder producers and how this influences optimal pathways for sharing knowledge and providing extension services. We found considerable potential for EI of smallholder farms in this region; most farmers grew insect pollinated crops and some farmers already employed EI practices, while others relied heavily on chemical pesticides. Based on physical, social and economic factors, three farm typologies emerged including ‘semi-commercial’, ‘market orientated’ and ‘subsistence’. These typologies influenced the appropriate EI practices available to farmers, as well as routes through which knowledge was shared and the extent to which extension services were utilised. We propose that to support effective uptake of EI practices, smallholder farm heterogeneity should be acknowledged and characterised in order to target the needs and capabilities of farmers and identify appropriate knowledge sharing and support pathways. The approach we take here has the potential to be employed in other regions globally