This study advocates that pesticide use has a significant negative impact on bee diversity in the Kole wetlands, reflecting the global trends of pollinator decline in agricultural landscapes. This finding is consistent with previous highlighting the detrimental effects of pesticide exposure on pollinator communities, particularly bees, in agroecosystems (Dicks et al. 2021; Knauer et al. 2024; Sahayaraj and Hassan 2023).
Impact of Pesticide Use on Bee Diversity:
The observed reduction in bee diversity in pesticide-treated fields, as indicated by lower species richness and Shannon diversity indices, suggests that pesticides are a major driver of bee decline in these agroecosystems. Bees are exposed to pesticides in various ways, such as through direct contact during application, exposure to residues, or ingestion of contaminated pollen, nectar, or guttation fluid (Ellis 2012; Hrynko et al. 2021). Owing to the use of systemic insecticides in the Kole paddy wetlands, the bees are susceptible to the chemical remnants present in plant tissues, including pollen and nectar, throughout the blooming period (Lundin et al. 2015). In addition, the life history traits such as foraging traits could influence the differential response of bees to pesticide exposure, with extensive foragers being most vulnerable to pesticides than limited foragers (Knapp et al. 2023; Tuell and Isaac 2010).
The distinct clustering of treated fields shown by NMDS, implies a more homogenized bee composition within them. Moreover, the species response plot shows that the treated fields were dominated by a few species such as Tetragonula sp. and Apis florea while there is a reduction in diversity of species such as Halictus sp. and Braunsapis sp. This pattern of shifting community structure reflects biotic homogenization, which refers to the increase in genetic, taxonomic, or functional similarity between two or more locations, as a result of species invasions and extinctions over time (Olden et al. 2008). This loss of functional biodiversity by biotic homogenization affect the wetland flora and eventually destabilizing the resilience of wetland ecosystems through altered pollinator dynamics. Even though biotic homogenization is documented in pollinator communities (Fourcade et al. 2021; White and Kerr 2007; Gossner et al. 2023), this study is inconclusive to confirm the trend in Kole wetlands and require long-term monitoring. However, our study strongly supports the hypothesis that intensive pesticide application can lead to a loss of species diversity within bee communities.
The significant temporal changes in bee diversity observed across both field types as well as the comparatively higher diversity in certain fields (T1 and T5) indicates the possibility of multiple factors beyond pesticide exposure, affecting bee populations. The could include aspects such as climate variability, field-specific characters like vegetation type and floral resource availability, or cumulative effects of pesticide exposure over time (Goulson et al. 2015; Raderschall et al. 2021). With the circumstances in consideration, the influence of field specific characteristics, i.e., bund vegetation to serves as reservoirs of biodiversity has paramount importance. While the agricultural practices intensify and climate become more variable, the ability of these habitats to support diverse bee communities is increasingly important for maintaining ecosystem resilience and function (Winfree et al. 2009).
Role of Non-Crop Habitats in Mitigating Pesticide Effects:
In the Kole wetlands, treated fields adjacent to bunds covered with dense native vegetation, were positively correlated with higher bee diversity, suggesting these areas may serve as refugia mitigating some of the adverse effects of pesticide exposure. The bunds provide critical resources such as nectar, pollen, and nesting sites that are often limited in monoculture-dominated landscapes (Forrest et al. 2015; Carvell et al. 2022). The hierarchical clustering dendrogram revealed that treated fields near diverse bunds shared a more similar species composition than the treated fields near to less diverse and barren bunds. This finding suggests that maintaining or enhancing the quality and diversity of non-crop habitats could help support more resilient bee communities by providing refugia against pesticide exposure. There is a noticeable similarity in species composition in T1-NC1 and T5-NC5 pair which could possibly be because of spill over effects from non-crop to treated field (Blitzer et al. 2012; Rague et al. 2022) However, non-crop fields exhibit higher overall diversity compared to their adjacent crop fields
In Kole paddy wetlands, where large non-crop areas are absent or limited, small habitat patches such as bunds and hedge grows play a vital role. These patches support ecosystem services by providing foraging opportunities and shelter for pollinators within a limited range, typically within 1 km of their nests (Rands and Whitney 2011). This finding aligns with the broader understanding that semi-natural habitats within agricultural systems, such as the bunds studied here, act as refugia and mitigate the adverse effects of intensive farming practices (Duelli and Obrist 2003; Lüscher et al. 2016). Not alone pollinators, the bund vegetation are sheltering and feeding sites for the migratory birds and unique water birds of wetlands. Nonetheless, the effectiveness of non-crop habitats as refuges is context-dependent. Undoubtedly, the presence of diverse non-crop habitats alleviates the negative effects of pesticide exposure to some degree, but the risk of pesticide drift from crop fields to wild habitats could potentially reduce their effectiveness as shelter for pollinators (Graham et al. 2024). This highlights the need for better management practices to minimize pesticide drift into non-crop habitats, such as applying pesticides during times when bees are less active and educating farm workers regarding targeted pesticide application (Karbassion and Stanley 2023, Mu et al. 2022). Additionally, enhancing habitat connectivity between agricultural and non-crop areas may further bolster bee populations by facilitating movement and resource access across landscapes (Buhk et al. 2018; Maurer et al. 2022; Westphal et al. 2015).
Implications for pollinator conservation and wetland management strategies
For responsible wetland management, it is crucial to integrate pest management strategies with pollinator conservation. Strategies such as reducing pesticide use, adopting less harmful alternatives (e.g., biopesticides), and enhancing the quality and connectivity of non-crop habitats could help mitigate the negative impacts of agricultural practices on bee populations (Singh et al. 2022; Inoka 2005). The observed positive relationship between bund flora diversity and bee diversity in adjacent treated fields suggests that promoting diverse, flower-rich habitats within agricultural landscapes could enhance pollinator support and contribute to more sustainable agricultural systems (Wratten et al. 2012). The studyfound out that unmanaged field bunds facilitated higher bee diversity and this call for actions at local level, to prioritize the preservation and restoration of these bunds that render ecosystem services at zero cost input. The efforts could include establishing wildflower strips, hedgerows, and other semi-natural features that provide critical resources and refuges for pollinators (Carvell et al. 2022; Hevia et al. 2021). Field margins with weeds are proved as pollinator friendly regions (Balfour and Ratnieks 2022; Bambaradeniya et al. 2004; Kleiman et al. 2020) and adopting this strategy could be a practical approach in Kole paddy wetlands where weeds are in abundance. The findings of Deeksha et al. (2022) reaffirms the utility of weeds as resource for pollinators who recorded 14 weed species supporting 25 insect pollinator interactions in the scrubland weeds of Northwestern Indian Himalayas
Additionally, farmer participatory approaches can be implemented, to educate of the ecological consequences of over dependency of pesticides and why pollinators are pivotal in sustaining their livelihood through wetlands. Farmer participatory approaches, as suggested by Garcia-Vega et al. (2024), should be prioritized to highlight how sustainable agriculture and pollinator conservation are essential for both ecosystem health and farmer livelihoods. Current practices followed by the Kole paddy farmers, such as burning and plowing the bund vegetation and other immediate non-crop habitats surrounding the crop fields, manual and machinery assisted weed pulling, contribute to biodiversity loss (Barros-Rodríguez et al. 2021). Raising awareness among farmers about the ecosystem services provided by bund vegetation and discouraging its mislabelling as a nuisance or 'undesirable,' could lead to foster better conservation outcomes. The cumulative efforts could help reconcile bee conservation with the human-induced menaces. Although this study is envisaged in specific geographical area, there is a need for regional and local-level research to tailor field-specific conservation and management strategies.
While this study attempted to provide insights on pesticide effects and impact of non-crop habitats as major objectives, it is limited primarily, by the short sampling period for assessing non-crop habitats and the lack of in-depth analysis of non-crop vegetation. To address the limitations, future studies should consider longer-term monitoring of bee communities and analyse a broader range of environmental conditions and landscape contents. This approach would provide insights into the temporal and spatial variations affecting bee communities and help to better understand the complex interactions between agricultural practices, habitat diversity, and pollinator communities.
