Seasonal variation in insect assemblages at flowers of Balanites aegyptiaca, an ecologically and socially important tree species in the Ferlo region of Senegal’s Great Green Wall corridor
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Abstract
Interactions between flowers and flower-visiting insects play central roles in ecosystem functioning. In addition to ensuring pollination, flower-visiting insects are also crucial for numerous other biotic interactions, using floral resources as fuel in their search for prey, hosts, breeding sites, and other resources. Studying insect-flower interactions may thus be strategic to conserve and restore biotic interactions in ecosystems heavily degraded by intensive land use and climate change, such as the arid savannas of the northern Sahel. We aimed to document for the first time the diversity of flower-visiting insects in this region and to examine whether restoration efforts of the Great Green Wall initiative have affected insect abundance and diversity. Using two capture methods, hand netting and pan traps, we inventoried insects visiting the flowers of Balanites aegyptiaca . This is the most abundant tree species in the region and is also of economic importance. We sampled three sites in a single locality: a “Restored” site from which livestock are excluded, an ”Unrestored” site in intensively grazed rangeland, and a topographical “Depression” site in a grazed area but with high tree density. Each site was sampled at three different periods to examine variation in this extremely harsh and seasonal environment. The open-access flowers of Balanites aegyptiaca are produced in multiple flowering events each year. We found a surprisingly high diversity of insects visiting its flowers, comprising 371 morphospecies from 10 insect orders, with a predominance of Hymenoptera and Diptera. Insect abundance, diversity, and species composition differed markedly between seasons. Bees appear to be important pollinators, particularly solitary bees of the family Halictidae, which were abundant in all seasons. Diptera, in particular several families of small flies, were also frequent visitors and were especially abundant and diverse in the wet season. Ants were especially abundant at flowers in the dry season, when few resources other than flowers and flower-visiting insects were likely available to them. Insect abundance and observed diversity differed only little between sites, but estimated total diversity (Chao1 richness) was highest in the Depression site. Insects visiting flowers of B. aegyptiaca included herbivores, decomposers, and parasitoids and predators of diverse arthropods, underlining the role of these floral resources in numerous facets of ecosystem functioning. The floral resources of B. aegyptiaca and other trees, which can flower throughout the year, are likely critical to ensure the persistence of numerous insect species. Integrating biotic interactions into ecosystem management is crucial for conservation and restoration in Sahelian ecosystems.
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The Sahelian thorn-bush savanna, located between the Sahara Desert and southern woodlands, is one of the world’s most environmentally degraded regions and is extremely vulnerable to climate change. Nevertheless, restoration initiatives implemented so far have been mostly plant (tree)-based, largely neglecting biotic interactions, which remain critically understudied.
Medina-Serrano et al. (2026) address this gap by investigating flower–insect interactions in Ferlo, a semi-arid sylvo-pastoral region in northern Senegal. This study provides a first assessment of the diversity of flower-visiting insects associated with Balanites aegyptiaca (L.) Delile (the desert date; Zygophyllaceae), a keystone and economically important tree species common in the region.
This work is particularly noteworthy for its methodological approach and ecological …The Sahelian thorn-bush savanna, located between the Sahara Desert and southern woodlands, is one of the world’s most environmentally degraded regions and is extremely vulnerable to climate change. Nevertheless, restoration initiatives implemented so far have been mostly plant (tree)-based, largely neglecting biotic interactions, which remain critically understudied.
Medina-Serrano et al. (2026) address this gap by investigating flower–insect interactions in Ferlo, a semi-arid sylvo-pastoral region in northern Senegal. This study provides a first assessment of the diversity of flower-visiting insects associated with Balanites aegyptiaca (L.) Delile (the desert date; Zygophyllaceae), a keystone and economically important tree species common in the region.
This work is particularly noteworthy for its methodological approach and ecological scope, especially given the lack of a comprehensive framework for restoring pastoral ecosystems in the region. The study was conducted across different periods of the year to capture temporal variation in flower-visitor communities in this highly seasonal environment. In addition, although spatially limited, it is valuable that monitoring was performed at sites differing in their management history and ecological characteristics. By combining complementary sampling techniques (hand netting and pan traps) across different sites and seasonal periods, the authors provide a robust and well-structured dataset. The comparison between restored and unrestored areas within the framework of the pan-African Great Green Wall initiative adds important applied value, offering insights into the ecological outcomes of large-scale restoration efforts.
The results reveal a remarkably high diversity of flower-visiting insects (overall, 2,907 individuals sampled, representing at least 371 morphospecies across 10 orders). As expected, different pollinator assemblages were captured by the two methods, partly reflecting the ecological habits of some taxa (e.g. nocturnal moths were mostly pan-trapped), underscoring their complementarity. The authors report the spectrum of Balanites aegyptiaca’s floral visitors, indicating their ecological roles. Key functional groups include solitary bees (notably Halictidae, present in all seasons) and some families of small flies (Diptera) as likely major pollinators, while ants—the most abundant visitors, with 10 different morphospecies—can act as nectar consumers or predators. Importantly, the study goes beyond pollination by illustrating how floral visitors contribute to a wide array of biotic interactions, including herbivory, decomposition, parasitism, and predation. These results highlight the ecological importance of the desert date in sustaining multiple trophic interactions, likely due to its year-round flowering and its “open” flowers, which offer easily accessible rewards to a wide range of insects.
The data analysis demonstrates strong seasonal variation in the abundance, diversity, and species composition of flower-visiting insect assemblages. The study also reports a slightly higher insect abundance in the Restored site, while observed species richness is significantly higher in both the Restored site and the Depression area compared to the intensively grazed Unrestored site, suggesting the likely importance of topographical depressions in this region as refuges for diverse organisms. Even though these findings provide limited insight into the effects of restoration actions on flower-visiting insect assemblages, when integrated into a broader ecological context they emphasize the role of year-round floral resources in maintaining biodiversity under extreme environmental conditions.
This manuscript underscores the importance of understanding and preserving biotic interactions to mitigate ecosystem degradation and support large-scale restoration initiatives such as the Great Green Wall. This integrative perspective significantly enhances the manuscript’s relevance for both fundamental ecology and applied conservation, providing a promising foundation for future long-term research aimed at improving our understanding of this system. Overall, I find this manuscript scientifically relevant to current challenges in biodiversity conservation and ecosystem restoration in the context of climate change.References
Natalia MEDINA-SERRANO, Anne-Genevieve Bagneres, Mouhamadou M. Ndiaye, Valentin Vrecko, Doyle McKey, Martine Hossaert (2026) Seasonal variation in insect assemblages at flowers of Balanites aegyptiaca, an ecologically and socially important tree species in the Ferlo region of Senegal’s Great Green Wall corridor. bioRxiv, ver.4 peer-reviewed and recommended by PCI Ecology https://doi.org/10.1101/2025.03.26.645493
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