Forest landscapes increase diversity of honeybee diets in the tropics

Honeybees (Apis mellifera) depend entirely on floral resources (pollen and nectar) in their surrounding landscape to satisfy their dietary needs. Honeybee diets in temperate areas have been well studied, and there is increasing evidence that floral diversity is critical for honeybee health. Tropical forests often contain high floral diversity but honeybee diets have been rarely studied in the tropics. We aim to compare the botanical sources in bee bread between landscapes with and without surrounding forest cover in the eastern highlands of Papua New Guinea. We collected bee bread from 24 hives across 8 sites over two years and examined floral sources, diversity measures and major plant groups using DNA metabarcoding. We identified a total of 89 taxa across 34 orders, 41 families, 84 genera and 61 species of botanical sources in bee bread. Bee bread from hives in sites with surrounding forest contained significantly greater species diversity (H’ Forest = 1.4, H’ No forest = 1.1) and species evenness (J Forest = 0.68, J No forest = 0.6). Trees were the most abundant source of bee bread, regardless of landscape, and constituted 52% of total abundance. Herbaceous plants, mostly introduced species, were the second most abundant floral sources at ∼ 26% of total bee bread abundance, particularly in forest landscapes. We found the most abundant sources such as introduced tree species Leucaena leucocephala (Fabaceae) and native tree species Syzigium unipunctatum (Myrtaceae) were foraged on in both landscapes; other common species included introduced species Hylodesmum nudifloram (Facbaceae) and Bidens pilosa (Asteraceae), and native food crop Entada phaseoloides (Fabaceae). Interestingly, many wind pollinated species were found in both landscapes including Araucaria (Araucariaceae), Pinus (Pinaceae), Nothofagaceae species and Poaceae species. Our work suggests that bees are seeking out floral tree resources even in landscapes where trees are scarce. Thus beekeeping in tropical environments would benefit from preserving remaining forest cover and incorporating more trees to existing, open landscapes to optimize the diversity in honeybee diets.