Orchid Bees are thought to have generalist diets, but take forest plants from the menu, and they become a lot less successful.

In forests as far north as Mexico and as far south as Argentina Orchid Bees fly. These insects play an important role in pollination in the tropics. Male orchid bees are known for their elaborate perfume-collecting behaviours, while females are considered generalists when it comes to gathering pollen to feed their offspring. However, a new study by Samuel Boff and colleagues, published in the Journal of Insect Conservation suggests that the pollen diets of these bees may not be as diverse as once thought, with deforestation leading to a narrowing of the floral resources available to them.

The study, conducted by researchers from Brazil, Germany and Mexico, analysed pollen from excreted waste in nests of the orchid bee Euglossa cordata across different vegetation types and levels of forest cover in Brazil. The study examined how bees foraged in the Atlantic forest, the grasslands of the Cerrado and the zone where the two ecosystems meet. The ecologists found that pollen diet composition differed significantly between vegetation types, with diet specialisation being lowest in forested areas and highest in disturbed habitats.

Euglossa cordata female foraging on the flower of Dichorisandra thyrsiflora, Itu (Brazil). Photo: Samuel Boff.

The team found a strong correlation between pollen richness, the number of brood cells, and the amount of forest cover. A search through other published results revealed this pattern was consistent across multiple Euglossa species, suggesting that the effects of habitat loss on pollen diversity are widespread among Orchid Bees. A closer study of the pollen shows that the bees were using various plants they were fond of foraging in above ground-level. Boff and colleagues write:

Although Euglossa collect resources at herbs and shrubs, most of plant genus display the habit of forest elements (e.g. trees, epiphytes and lianas). Our findings may help to explain the use of connected forest fragments by bees to enable them to inhabit forested sites (Dick et al. 2004) and their lower population sizes in open areas (Silveira et al. 2015) and urbanized areas (Cândido et al. 2018).

Boff et al. 2024

The findings suggest that even generalist species like Euglossa cordata, which are adapted to forage on a wide variety of plants, are still heavily dependent on the rich floral resources found in forests. The loss of these habitats, particularly the trees and lianas that provide essential pollen sources, could have cascading effects on orchid bee populations and, in turn, on the numerous plant species they pollinate.

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Boff, S., da Luz, C.F.P., Raizer, J., Pinto, G.S., Santos, L.F., Freitas, B.M., da Silva, C.I., Quezada-Euàn, J.J.G., Soro, A. and Alves-dos-Santos, I. (2024) “Deforestation narrows pollen diet diversity of generalist orchid bees,” Journal of Insect Conservation. Available at: https://doi.org/10.1007/s10841-024-00575-2.

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