Mapping floral resources for honey bees in New Zealand at the catchment scale

Abstract

Honey bees require nectar and pollen from flowers: nectar for energy and pollen for growth. The demand for nectar and pollen varies during the year, with more pollen needed in spring for colony population growth and more nectar needed in summer to sustain the maximum colony size and collect surplus nectar stores for winter. Sufficient bee forage is therefore necessary to ensure a healthy bee colony. Land-use changes can reduce the availability of floral resources suitable for bees, thereby increasing the susceptibility of bees to other stressors such as disease and pesticides. In contrast, land-based management decisions to protect or plant bee forage can enhance pollen and nectar supply to bees while meeting other goals such as riparian planting for water-quality improvement. Commercial demand for honey can also put pressure on floral resources through over-crowding of hives. To help understand and manage floral resources for bees, we developed a spatial model for mapping monthly nectar and pollen production from maps of land cover. Based on monthly estimated production data we mapped potential monthly supply of nectar and pollen to a given apiary location in the landscape. This is done by summing the total production within the foraging range of the apiary while subtracting the estimated nectar converted to energy for collection. Ratios of estimated supply over theoretical hive demand may then be used to infer a potential landscape carrying capacity to sustain hives. This model framework is quantitative and spatial, utilizing estimated flight energy costs for nectar foraging. It can contribute to management decisions such as where apiaries could be placed in the landscape depending on floral resources and where nectar limited areas may be located. It can contribute to planning areas for bee protection or planting such as in riparian vegetation. This would aid managed bee health, wild pollinator protection, and honey production. We demonstrate the methods in a case study in New Zealand where there is a growing demand for mānuka (Leptospermum scoparium) honey production.

Citizen science monitoring reveals links between honeybee health, pesticide exposure and seasonal availability of floral resources

“…The loss of these often-early flowering species has led to important ‘drought’ periods of floral resource deficiency in these systems. Such early season deficits in resource availability may be a particular threat to honeybees, and potentially other eusocial species, by limiting resource availability as a point in the season where colony growth should be maximised 35 . Of these other land uses, there was some suggestion that urban environments may be likely to provide a greater diversity of potential plant species to forage upon, something reported in several other studies 29 , 57 .…”

“…While pollinators forage dynamically across varying scales to compensate for such temporal resources variability, ultimately landscape diversity and quality places an upper limit on what can be extracted to support population growth 31 . In the case of honeybees, there is a greater requirement for pollen to support colony growth in the spring, while nectar becomes more important later in the year for maintaining colony size and for storage as honey 35 . As such, temporal variability in flowering resources may interact with key periods of specific nutritional requirements to have unexpected negative effects.…”

Varroa Appears to Drive Persistent Increases in New Zealand Colony Losses

“…New Zealand spans 12 degree of latitude and has a temperate climate, experiencing only a mild winter. The country has a diversity of native and exotic flora that provide abundant pollen and nectar resources, allowing honey bee colonies to flourish at comparatively high stocking rates [ 11 ]. Of particular note, native trees in the Myrtaceae family (e.g., Leptospermum scoparium (mānuka), Metrosideros excelsa (pōhutukawa), Metrosideros robusta (rātā), and Kunzea ericoides (kānuka)) provide honey bees with substantial seasonal nectar yields and provide monofloral honey crops.…”

What effects must be avoided, remediated or mitigated to maintain indigenous biodiversity?

“…Regenerating ecosystems may also be important for evolution and adaptation in new environments and disturbance regimes under climate change, and for ecosystem services (e.g. water purification, flood mitigation, or wild foods like honey; Ausseil et al 2018).…”