2.1 Literature survey

To ascertain the distribution of research articles on pollination ecology, in February 2023, we surveyed peer-reviewed and Scopus-indexed articles from the Web of Science database, covering publications from 1990 to early 2023. To compare India's scientific contributions in pollination biology with global trends, we conducted a comprehensive literature search using the terms ‘Pollination Biology’ and ‘Pollination Biology AND India’ in article titles, keywords and abstracts. We then carefully selected papers that specifically addressed pollination studies. After eliminating irrelevant articles from our analysis, we organized the collected data chronologically. The screening process, exclusion criteria and final data set adheres to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines (Page et al., 2021; Supporting Information S1: Figure 1). We then categorized these publications based on the nature and type of plants involved, such as crops (‘Pollination biology AND crops’), non-crops (‘Pollination biology NOT crops’), medicinal plants (‘Pollination biology AND medicinal plants’), endemic species (“Pollination biology AND endemic plants’), threatened plant species (‘Pollination biology AND threatened plants’) and trees (‘Pollination biology AND trees’). We compared these categories for articles published in India against the overall pool of publications. Additionally, we identified studies addressing different aspects of pollination and plant reproductive fitness, encompassing topics such as breeding systems, mating systems, inbreeding depression, self-incompatibility, pollination limitation and pollinator decline. We also organized the studies year by year, categorizing them by various pollination syndromes such as wind, bee, fly, moth, bird, butterfly and bat pollination.

2.2 Economic potential of pollination

To determine the economic value of pollination, six economically important and pollinator-dependent crops were selected: Cajanus cajan (pigeonpea), Cicer arietinum (chickpea), Brassica napus (rapeseed), Helianthus annuus (sunflower), Gossypium spp. (cotton), and Theobroma cacao (cacao). These were chosen because (i) these are all pollinator-dependent, (ii) they represent all plant forms, that is, herbs/shrubs/trees, (iii) these are cash crops that have high minimum support price for farmers set by the government, and (iv) these crops are popular in the domestic market (https://www.indiastat.com/). The production value method was used to assess the economic value of pollinator services (Winfree et al., 2011). This method applies the formula EVp = D × P × Y, where EVp represents the Economic Value of the pollinator. In this formula, D signifies a crop's dependency on pollinators, P represents the crop's economic value in terms of the minimum support price (MSP) and Y corresponds to the crop's yield in kilograms per hectare. The pollinator dependency rate data employed in this calculation was sourced from Gallai et al. (2009) and Klein et al. (2007). Data on crop yield and prices in India (2012–2022) were obtained from the Ministry of Agriculture and Farmers Welfare, a government entity and Indiastat (https://www.indiastat.com/), an extensive e-resource providing socioeconomic statistical information. Year-wise Minimum Support Prices (MSP) for various crops were collected from the Farmers Portal (farmer. gov. in) and the Directorate of Cashewnut & Cocoa Development (DCCD). Information on the categories and usage of chemical and bio-pesticides from 2014 to 2021 was also sourced from Indiastats.

Data visualization was done using the ggplot2 package in R ver. 4.3.0 (R Core Team, 2020; Wickham et al., 2016).

3.1 The past: How pollination research has evolved in India

In the 20th century, certain Indian biologists (see Shaanker and Ganeshaiah, 1993) and naturalists began delving into the field of pollination ecology, primarily focusing on improving agricultural production to ensure food security. This led to research centred around the manipulation and management of pollinators to increase crop yield. The reduction in forested areas due to habitat destruction and changes in land use also prompted a shift towards conservation-oriented pollination research in India (Aluri, 1990; Shaanker and Ganeshaiah, 1993). In the 21st century, baseline data collection on pollination biology continued, resulting in very few community-based studies (Devy and Davidar, 2003; Nayak and Davidar, 2010). However, much of the literature suggests that, thus far, research on pollination has predominantly focused on individual plant species, particularly their reproductive health, fitness, rewards, cues and pollination efficiency within a limited group of taxa (such as members of Apocynaceae, Araceae, Fabaceae, Lamiaceae, Solanaceae to name a few). Holistic research considering both plant and pollinator perspectives remains lacking. Very few studies have concentrated on the taxonomy, diversity and behaviour of wild and native pollinators. The absence of quantitative assessments of wild pollinator density, diversity and their impact on agricultural output has been an impediment in understanding possible constraints in pollination services of our crop as well as wild species (Shivanna et al., 2020).

India is one of the 12 megadiversity countries. It constitutes 2.4% of the land area accounting for 7%–8% of the species of the world including about 45,000 species of plants (Bawa et al., 2021). Currently, angiosperms constitute 39.2% of the India's plant diversity of which 28% are endemic to the country (https://bsi.gov.in/). Yet, India's contribution to pollination literature has been just 4.4% (1395 out of 31,322 research papers). Primary reason for this, as represented by the slow rate of research (Figure 1a), is perhaps the scarcity of trained manpower, insufficient research funding and lack of interdisciplinary approach in research. Also, the vagaries of field-work often force young researchers to choose lab-oriented experimental studies. The data clearly highlights the scarcity of Indian studies across plant groups. Despite the high degree of endemism, only 0.26% of these plants have been studied in relation to pollination ecology. Similarly, there are very few studies on medicinal and threatened species (Figure 1b). Even for plants where pollination biology has been studied, data is limited in key areas such as identifying pollinators amongst floral visitors, understanding breeding/mating systems and assessing pollinator/pollination limitation, all of which are extremely important for evaluating natural recruitment. These figures are also negligible when compared to global research being conducted thus far (Figure 1c), with a majority of published studies focussing on melittophily (bee pollination) (Figure 1d).

3.2 The present: Why pollination research is important in India

Since 2000, pollination research in India has shown an increasing trend, though studies on bee pollination have only seen a marked increase since 2015 (Figure 2). This rise in bee-related research may be attributed to government policies promoting beekeeping and aforementioned push toward ‘Sweet Revolution’ (a national government initiative aimed at increasing farmers' incomes through scientific beekeeping and the production of honey and associated products) (https://www.indiastat.com/). However, several economically and ecologically important plants are pollinated by other animal groups such as birds (ornithophily), bats (chiropterophily), moths (phalaenophily), flies (myophily) and butterflies (psychophily) (Hill, 1997; Kearns et al., 1998; Klein et al., 2007; Ollerton et al., 2011; Ollerton, 2021; Subramanya and Radhamani, 1993). These alternative vectors are known to legitimately serve more than 70% of the pollinator-dependent angiosperms globally; yet research on these interactions remains scarce compared to melittophily (Rader et al., 2020). To ensure food security, conservation of biodiversity and ecological balance, it is essential to study pollination across all pollinator guilds/syndromes, which should be investigated at broader biological scales, such as communities or biomes.

Incorporating ecological elements is crucial for comprehending the reproductive fitness and regenerative capacity of plant species (Barrett, 2010; Ren et al., 2012). Community ecology studies concerning plant interactions with pollinators and antagonists are essential for organized reintroduction of species into fragmented habitats and for setting conservation priorities. Research on functional biology, trade-offs linked to floral resource availability, pollinator ecological niches, pollinator cognitive behaviour and pollination ecotypes plays a pivotal role in our understanding of their eco-evolutionary stability (Mayer et al., 2011). Exploring these adaptations deepens our knowledge of the diverse array of interactions between plants and pollinators and their significance within ecosystems.

The presence of a diverse range of pollinators is of paramount importance for ensuring the stability and resilience of the pollination process. Documenting the diversity and geographical distribution of pollinators across different regions in India would play an essential role in devising strategies to conserve and strengthen their populations (Tandon et al., 2020). India hosts over 700 bee species, with only five classified as social bees (Orr et al., 2021), highlighting the significant untapped potential of alternative pollinators for agricultural benefits. It is essential to gain insights into the habitat and floral preferences of solitary bees, as this knowledge is critical for emulating natural habitats, thereby facilitating the diversification of pollinators within agricultural settings (Shivanna, 2022). Solitary bees are often more effective than honeybees in terms of pollination, as they can adapt to various temperatures and other variables (Vaughan and Black, 2008). Moreover, owing to their solitary behaviour, only a limited number of individuals can oversee the populations of flowering plants and the well-being of both plants and bees relies significantly on the mutualistic interactions they engage in within the plant community (Adit et al., 2022). In an effort to revive declining pollinator diversity, many Western countries are promoting the use of ‘bee-hotels’ and ‘bee-gardens’ which serve as the insect equivalent of birdhouses. These have gained popularity for conserving native bee taxa in both rural and urban environments (Prendergast, 2023). The floral resources, such as flowering strips, wildflower meadows and hedgerows, can also be an efficient approach, as they act as stand-in resources to bridge the gap between successive seasonal crops (Bishop et al., 2022; Osterman, 2022). Some studies show a remarkable increase in crop yield due to increased pollinator assemblage in the agricultural fields adjacent to the forest patch (Aizen and Feinsinger, 2003; Vergara and Badano, 2009). Considering the Indian scenario of agricultural set-up, there are enormous opportunities to harness the synergistic effect of wild pollinators in agricultural zones by creating floral resources and in those near forest patches (Bhattacharya and Basu, 2018). Restoration of fragmented forests can not only improve the diversity of pollinators but also result in enhanced foraging efficiency which have direct consequences on improving fruit and seed production (Blüthgen and Klein, 2011).

3.3 The future: What road should pollination research in India take

Wild pollinators worldwide are encountering numerous challenges, largely due to habitat loss, changes in land-use pattern, heavy use of insecticides and pesticides, shifts in climate, along with other stressors like invasive species and the spread of pests and diseases (Kevan and Viana, 2003; Potts et al., 2010; Vanbergen et al., 2020). Extensive studies carried out globally have highlighted the declining trend in the density and diversity of wild pollinators which also contribute to pollination of wild and crop species (Nath et al., 2023). This has led to deficiency of pollination services leading to the ‘global pollinator crisis’ (Kearns et al., 1998; Tylianakis, 2013).

There is a pressing need to identify pollinator hotspots in India, locations where investing in pollinator conservation will yield the highest returns (such as the Eastern Himalayas, Western Himalayas, Western Ghats, Deccan Plateau and Northeast India). These regions have exceptionally high diversity and endemism of plants and potential pollinators. The affluence of pollinator groups in these hotspots can offer an avenue for identifying alternate pollinators and provide information about pollinator decline, besides helping in making policies related to the conservation of the forest trees and RET (Rare, Endangered and Threatened) species. Due to the rich biodiversity of both plants and pollinators in these regions, sustainable agricultural practices such as agroforestry and buffer plantations also have the potential to yield greater economic returns (Barrios et al., 2018; Udawatta et al., 2021).

Over the past two decades, significant attention has been devoted to climate change and its impact on the altitudinal migration of plant and pollinator species, along with their phenology and pollination process (Bartomeus et al., 2011; Cleland et al., 2007; Settele et al., 2016; Hegland et al., 2009). Nevertheless, in India, there is a notable absence of concrete data on these aspects. While some studies have explored the short- and long-term consequences of climate change on pollinator decline, most lack empirical insights into the intricate relationships between plants and pollinators (Bhatt et al., 2018; Reddy et al., 2013). Furthermore, our understanding of how various drivers of climate change synergistically affect these ecosystem services remains limited. The introduction of invasive plants, which often adapt better to climate fluctuations, poses a significant threat to the well-being of native plants and their pollinators (Giejsztowt et al., 2020). These exotic plants typically propagate through self-pollination and frequently fail to provide appropriate reward to the indigenous floral visitors (Bradley et al., 2009; Giejsztowt et al., 2020). As both climate fluctuations and invasive species threaten pollinator-dependent crops, integrating pollination ecology into climate-smart agricultural practices is essential to ensure global food security (Sharma et al., 2022).

The growing demand for increased food production has led to a substantial rise in the use of chemical pesticides to boost crop yields (Liu et al., 2015). However, this practice has severe negative consequences on the well-being of various pollinator groups and carries serious socioeconomic costs. Numerous studies indicate that these chemical pesticides not only harm bee colonies but also affect wild insect and bird pollinators (Biesmeijer et al., 2006; Sponsler et al., 2019). The primary cause of the widespread decline in bee populations in Europe can be attributed to the utilization of a specific class of pesticides known as neonicotinoids (Auteri et al., 2017). These chemicals can disrupt the cognitive processes of insects and hinder their ability to learn about floral attractants. This can lead to a complete loss of fundamental associations vital for their survival, such as connecting floral scents with food sources (Balbuena et al., 2015; Baron et al., 2017; Belzunces et al., 2012). Consequently, bees perish due to their inability to adequately nourish themselves. India relies heavily on pesticides, with an annual average consumption of 59,876.14 metric tons (2014–2021), which accounts for nearly 2% of the world's pesticide consumption (https://www.indiastat.com/; Zhang, 2018). Out of 293 pesticides registered in India 130 are considered hazardous by World Health Organization (Pandey, 2023; Soman et al., 2024). There are no studies on the impact of these pesticides on pollinators. Research into the effects of these chemicals on pollinator health would contribute to the development of integrated pest management policies and alternative solutions. Such strategies would help to conserve pollinators without compromising crop yields. The increasing use of biopesticides is a promising trend in India (Chakraborty et al., 2023). The average annual consumption is currently at 7110.71 metric tons (2014–21) and shows a steady increase over the years (Figure 3). Gradual transition to integrated pest management and biopesticides can reduce our dependence on chemical pesticides. This shift has the potential to substantially combat the pollinator decline and, in the long run, enhance crop production by harnessing the full benefits of this mutually beneficial ecosystem service (Tripathi et al., 2020).

The impact of plant-pollinator interactions is huge in terms of their economic value (Potts et al., 2016). Several authors have shown the importance and role of pollinators in terms of ecosystem services and economic value (Potts et al., 2011). It is estimated that the direct contribution of insect pollination to Indian agriculture is substantial, amounting to US$22.5 billion, which constitutes 8.72% of the total value of agriculture annually (Chaudhary and Chand, 2017). Data for six fully or partially pollinator-dependent crops in India demonstrates the substantial economic value of pollinator services per hectare (Table 1). The greater a crop's dependence on pollinators, the higher the economic potential of the pollinators.