Pollinators play important roles in providing pollination services, maintaining biodiversity, and boosting crop production. Even though pollinators are essential to the environment and agriculture, their decline has been noted across multiple studies in the recent past. Both natural and anthropogenic factors have contributed to their decline. Much of the focus has been placed on climate change, habitat loss, pests and pathogens, and synthetic pesticides, but relatively little is known about the effects of biopesticides. Biopesticides are biological control agents derived from living organisms and are classified into three groups: microbial, biochemical, and plant-incorporated protectant-based products. Biopesticides are formulated similarly to their synthetic counterparts and are readily available and used within urban and agricultural settings by pest management experts and household residents. The general public and much scientific literature support the prevailing idea that biopesticides are environmentally safe and pollinator friendly in comparison with synthetic versions. However, such generalizations are based on studies with a few key pollinator species and may not be relevant to several other species that provide crop pollination services. Studies focused on native pollinators have shown that some biopesticides have lethal and sublethal effects. Because each biopesticide exhibits varying effects across pollinator species, it could be dangerous to generalize their non-toxicity across taxa and environmental settings. In this article, recent research in this direction is discussed.

Insect pollinators provide a critical ecosystem service by increasing the yield and quality of many globally important crops, with both managed and wild pollinators playing an important role. The protection of pollinators has gained increasing attention in recent years due to threats to pollination services such as climate change, pesticide usage, and natural habitat loss. However, implementing effective protective measures is challenging, as the level of crop dependency on insect pollination and the specific pollinator species important for different crops are often unknown. Moreover, the adoption of pollinator-friendly land management practices by growers frequently requires external support, which is often not available in many regions. The private sector has a vested interest in safeguarding pollinators given that numerous companies rely on insect-pollinated products within their supply chain and, thus, they have the potential to play a key role in supporting growers. However, at present, only a limited number of companies take action on pollinator protection, largely due to a lack of understanding regarding the risks faced by pollinators and the most effective support mechanisms. To investigate some of these knowledge gaps, this thesis used avocado (Persea americana) as a study crop. Avocado is a globally important insect-pollinated fruit, for which little is known regarding pollination dependency, the contribution of wild pollination services and effective tools for sustainable management of avocado pollination. The first objective was to determine the extent of the contribution of insect pollinators to avocado production, and which insect taxa are the most important pollinators in different growing regions. The second objective was to investigate the impact of proximity to natural habitats on pollinators in avocado orchards, with a focus on the important avocado-growing region of Chile. The final objective was to develop a tool that private sector companies can employ to develop effective strategies for safeguarding pollinators, using an avocado supplier company as a case study. Chapter 2 involved a literature review and meta-analysis of existing avocado pollination studies and showed that insects contributed greatly to pollination, fruit set, and yield. Honeybees (Apis mellifera) were important pollinators in many regions due to their efficiency and high abundance, however, many wild pollinators also visited avocado flowers and were the most frequent visitors in over 50% of studies. Stingless bees (Meliponini spp) and blow flies (Calliphoridae spp) were identified as effective avocado pollinators, although for the majority of flower visitors’ data on pollinator efficiency was lacking. Chapter 3 reports findings from pollinator surveys and controlled pollination experiments in three avocado orchards in central Chile. The result showed that over 70 different insect species visited avocado flowers and that wild pollinator abundance, visitation rate, diversity, and richness were significantly higher in areas directly adjacent to a natural habitat border. The pollinator exclusion experiments showed that insect pollinators contributed significantly to avocado production, with almost no fruit set when pollinators were excluded. Hoverflies and flies were identified as effective avocado pollinators due to their high flower visitation rate, with fruit set positively correlated with the abundances of these taxa. Finally, Chapter 4 developed a tool to assist companies in formulating and implementing effective pollinator protection strategies. The tool comprises of seven activities, including new and existing desk-based methodologies, grower surveys, and informant interviews. The activities will help companies to 1) understand the threats to pollinators in different supply regions, 2) recognize the significance of pollinators to their business 3) assess the current implementation of pollinator actions, and 4) identify additional measures to better support pollinators. Application of this tool to an international company sourcing and supplying avocado indicated that increasing knowledge transfer to growers and supporting their participation in environmental certification schemes could serve as effective strategies for pollination protection. The overall results from this thesis underscore the importance of insect pollinators in avocado production, with wild pollinators and the natural habitats which support them playing significant roles. To optimise yields, growers should implement land management practices that protect and restore natural areas within and around their orchards. Furthermore, the industry tool developed in this thesis provides private sector companies with a means to enhance pollinator protection by providing a mechanism to develop effective safeguarding strategies. Its potential implementation could greatly benefit growers and pollination services worldwide.

Urbanization is a primary threat to biodiversity and the functioning of both natural and agro-ecosystems. Especially in the Global South, expanding cities increasingly encroach fertile agricultural lands, questioning the viability of maintaining agricultural activities in urbanized landscapes. Yet, the growing interest in urban agriculture may offer an opportunity to improve the sustainability of cities. Indeed, urban agriculture often consists in small-scale wildlife-friendly farming, and thus can provide resources and habitats for various organisms, while locally producing food within and around cities. However, the effects of urbanization on agricultural biodiversity and the delivery of ecosystem services upon which urban smallholders depend such as biological pest control and crop pollination are little understood, especially in global urbanization hot spots from the tropics. This thesis is part of a larger interdisciplinary and collaborative research project between Germany and India that aims to investigate how urbanization affects urban agriculture. This project takes place in Bengaluru, an emerging megacity in South India, which exemplifies key characteristics of urbanization and serves as an in situ laboratory to assess their effects on agro-ecological and socio-economic attributes of urban agriculture. Within the project, this thesis focuses on agricultural biodiversity and associated services across rural-urban landscapes. The thesis is divided into four chapters. The first three chapters investigate how urbanization drives the spatial and temporal dynamics of service-providing organisms, namely birds and bees. Going one-step further, the fourth chapter, as a case study, looks at how urbanization affects the delivery of pollination service to mango, one of the most important tropical fruit crops. Chapter 1 reports on the drivers of taxonomic and functional beta-diversity of farmland birds along an urbanization gradient. This chapter demonstrates that urbanization acts as an environmental filter and homogenizes farmland bird communities, and discusses the potential implications for ecosystem services. Chapter 2 focuses on the functional responses of farmland bees to urbanization, and how urban farm characteristics can modulate these responses. It emphasizes how some functional groups of bees thrive in urban landscapes while others suffer, and how results from studies conducted in tropical countries do not necessarily align with that of studies from temperate regions. It also highlights how certain urban agricultural practices, such as crop diversification or flowering field margins, can promote bee communities. Chapter 3 provides novel insights on an understudied topic, namely the effects of urbanization on spatial and temporal dynamics of plant-pollinator interaction networks. The results show that urbanization alters the spatiotemporal dynamics of plant-pollinator networks, by amplifying the seasonal turnover of their interactions. This study demonstrates that environmental, spatial, and temporal gradients interact to shape the dynamics of plant-pollinator networks. Finally, Chapter 4 serves as an example on how the direct and indirect effects of urbanization and farm management influence the delivery of ecosystem services, using mango production (Mangifera indica) as a case study. The results indicate that mango production can be maintained at a profitable level in urbanized landscapes with insect pollinators more than tripling final yield. However, insecticides applications had negative effects on insect pollinators, in turn reducing mango yield. This suggests a trade-off between conventional pest control and mango pollination. In conclusion, this thesis displays the variable effects of urbanization on the diversity of different animal groups and related ecosystem services. Whereas farmland bird communities homogenize with growing urban areas, the response of farmland bees varies largely among taxonomic and functional groups. This thesis also emphasizes when the findings align or differ between studies conducted in tropical vs temperate regions, and highlights that generalizations drawn from studies conducted in one region do not necessarily apply to the other. Further, our result suggests that urban farming can be maintained at a profitable level, at least in low intensity level urbanized landscapes. Finally, this work suggests that small-scale urban agriculture, if managed in a sustainable way, might be a promising strategy to reconcile biodiversity conservation and food production within and around cities, thus increasing their sustainability. | 2024-07-25