edited by G. Clark, reviewed by R. Egan
Hylaeus navai Dorey, Davies, and Parslow sp. Nov. Female lateral habitus
(A), face (B), dorsal mesosoma (C), and lateral head (D) (scale bar = 0.50 mm). Credit: Frontiers in Ecology and Evolution (2024). DOI: 10.3389/fevo.2024.1339446
The decline of pollinator species due to habitat loss and pesticide use over recent decades has been a global concern. Pollinators like bees and butterflies support both wild plants and agricultural food production, but many species are threatened and remain poorly studied. It's estimated that bees, in particular, pollinate between 78% and 94% of all plant species.
One bee species, discovered in Fiji only two years ago, appears to represent an extreme case of this kind of population decline. A new study, published in Ecology and Evolution, indicates that this species has experienced a dramatic decline in its population over the last 150 years—a time span that happens to coincide with European colonization of the islands.
Fiji's previously overlooked Hylaeus bees
In 2024, researchers discovered six Hylaeus species endemic to Fiji. These native Hylaeus bees were largely overlooked until researchers began routinely sampling treetops, where the bees tend to live, feed and reproduce. The canopy-dwelling bees were also small, averaging about 3.9 mm (0.15 inches) in length.
The team involved in the new study writes, "The small-bodied Fijian Hylaeus carry pollen internally and appear to exhibit specialization on red-flower canopy plants, challenging historical assumptions that bees cannot see red. As probable canopy/forest specialists with potentially limited foraging ranges due to their small body size, these taxa are likely vulnerable to habitat change."
Demographic history of H. navai in Fiji in relation to human settlement and environmental change.
Credit: Ecology and Evolution (2026). DOI: 10.1002/ece3.74366
Recent dramatic population declines revealed
To gain insight into the ecology, genetic health, population structure and distribution of the six Hylaeus species, the team sampled low vegetation and tree canopies at 54 locations on Fiji's main island, Viti Levu. They analyzed DNA from 94 bees across four species. Because H. navai was more abundant in their sample, the researchers focused their population analyses on this species. Their analyses combined genetic reconstruction, historical collection records and environmental models.
Genetic evidence showed reduced diversity and elevated inbreeding among H. navai, indicating the bees had experienced a severe population bottleneck. DNA-based reconstruction suggested an approximately 99% decline (roughly 82% to nearly 100% when uncertainty was considered) in H. navai's effective population size over about 150 years in a series of three distinct bursts, which the team says pushes the bees into endangered territory.
The study authors write, "Over three separate 10-year periods in H. navai's demographic history, we inferred population size declines of 61%, 76% and 82%. These declines provide evidence to justify an International Union for Conservation of Nature (IUCN) assessment, with population size declines of this magnitude aligning with criteria for a listing of critically endangered."
Links to colonization, invasive trees and cyclones
H. navai's population decline aligns with Fiji's increasing human population since it was officially colonized by Britain in 1874. Since then, the islands have experienced increased deforestation, agricultural expansion and habitat fragmentation, likely affecting the bees. Historical records and the near absence of these bees from surveyed lowlands suggest a possible retreat from lower elevations.
This also coincides with an increase in the invasive African tulip tree, which was introduced to Fiji in 1936 as an ornamental plant. The tree produces red flowers, which likely attract the bees. However, its nectar is known to be toxic to honey bees and stingless bees, making it a potential "ecological trap" for H. navai.
The team says that cyclones may also play a role in H. navai's decline. Cyclones have destroyed tree cover and nests and changed microclimates, ultimately reducing suitable habitats for Hylaeus species. Currently, the bees are estimated to be restricted to only 1.4%–2.4% of Fiji's terrestrial area, mostly at higher elevations.
The team notes that all of these are proposed explanations, not yet demonstrated causes. They say future work should test whether African tulip tree nectar actually harms Fijian Hylaeus and should examine how warming and cyclone damage affect the remaining highland habitat.
The study authors write, "Empirically identifying and counteracting the major drivers of decline is of immediate conservation importance for all Fijian Hylaeus bees. We suggest that the Fijian Hylaeus can serve as a model system for understanding past declines in cryptic taxa."
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