Honeybees (Apis mellifera) depend entirely on pollen and nectar from flowers in their surrounding landscape to satisfy their dietary needs. Studies of honeybee diets in temperate areas are showing increasing evidence that floral diversity is critical for honeybee health. In contrast, honeybee diets have rarely been studied in the tropics. Tropical forests often contain high floral diversity, but many tropical forests are under threat globally. Papua New Guinea has some of the highest floral richness of any tropical island in the world, with a growing beekeeping industry. However, there is little information on the importance of tropical forests for honeybee diets in Papua New Guinea. This thesis compared honeybee diets in landscapes with and without forest in the Eastern Highlands of Papua New Guinea. In particular I compared the diversity, species composition and nutritional profile of bee bread and honey collected by honeybees in these landscapes. I collected n=162 beebread samples from 24 hives across 8 sites over two years in four sites with surrounding forest cover and four sites without forest cover in the Eastern Highlands of Papua New Guinea. I used DNA metabarcoding to identify plant species, estimate diversity measures and classify the major plant groups important to managed honeybees. I found bee bread from hives in sites with surrounding forest cover 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) compared with no forest sites. I identified a total of 89 taxa across 34 orders, 41 families, 84 genera and 61 species of botanical sources in bee bread. Native species and trees Leucaena leucocephala and Syzigium unipunctatum were the most abundant plant sources of bee bread. Other major sources included near threatened species Helicia latifolia, followed by herbaceous plants that were composed of mostly introduced species Hylodesmum nudifloram and Bidens pilosa. Fatty acids are a critical component of managed honeybee diets, and a variety of fatty acids are necessary to provide a ‘complete’ nutritional profile that supports honeybee health. I compared the concentration and diversity of fatty acids in the bee bread samples described above. I examined fatty acid concentrations in bee bread using GCMS and explored their relationship with the presence of forest in surrounding landscapes and diversity measures from bee bread. I identified 12 fatty acids in total from bee bread samples. Fatty acids consisted of 43% saturated and 57% unsaturated lipids by yield of bee bread. Total fatty acid diversity in bee bread increased with Shannon-Wiener diversity of bee bread (rho=0.21) and Pielou’s evenness (rho=0.23). The ratio of essential omega 6 to omega 3 was high at 3.8:1, and did not differ significantly between forest and no forest landscapes. Lauric acid was higher in no forest landscapes compared with forested landscapes. In contrast, myristic acid palmitoleic acid, and stearic acid were higher in forest landscapes compared with no-forest landscapes. This thesis also assessed the effect of forest cover surrounding hives on the floral composition, diversity and richness of nectar sources in honey in the highlands of Papua New Guinea. I collected a total of 42 honey samples (2 frames per hive x 3 hives x 8 sites) from 8 apiary sites, four with and four without surrounding forest cover. I identified a total of 61 plant taxa in 24 orders, 34 families, 52 genera and 46 species in honey samples. Honey was significantly different in floral composition (R2= 0.08) between forest and no-forest landscapes but was not significant different in diversity. I found tree species Helicia latifolia, Horsfieldia hellwigii, Pometia pinnata, the common bean Phaselous vulgaris and mistletoe provided the highest relative abundance of all functional plant groups identified in honey samples. I also found that honey was significantly different in species composition (R2= 0.32) and higher in diversity, richness and evenness compared to flora identified in bee bread and mineral composition of honey was unaffected by the presence of forest but was rich in potassium. My thesis highlights the significance of trees as pollen and nectar resources for honeybees in the tropics. The findings suggest bees will travel to seek out tree resources in landscapes where they are scarce. I also demonstrate that higher floral diversity in tropical landscapes impacts honeybee health by increasing the diversity of fatty acids in beebread. Furthermore, I show the diversity, richness and evenness from nectar sources in honey is significantly higher than that of pollen sources from bee bread and is not dependent on the presence of forest in the landscape. Based on these results I recommend conserving remaining rainforest and planting trees in open landscapes for honeybee health and improve management practices for beekeepers in the Eastern Highlands of Papua New Guinea.