Improving spatial arrangement of honeybee colonies to avoid pollination shortfall and depressed fruit set

Abstract

1. Pollination shortfalls affect yield of many crops, and the use of managed honeybee colonies is a common practice for addressing the problem. However, colony density and arrangement strategies are not generally based on replicated scientific trials, so there is considerable uncertainty regarding effectiveness of different practices. We address this problem with experiments in almond orchards in south-east Australia, considering impacts on honeybee pollen foraging and fruit set. 2. We examined the effect of distance from colony location on the depletion rate of pollen from flowers near (~40 m) and far (260-490 m) from colonies in almond orchards. We assessed pollen loads of 950 flowers in total, collected at four times of day (9-9:30 h, 11-11:30 h, 13-13:30 h and 15-15:30 h), from 8 near : far pairs. We also surveyed fruit set on nearly 900 trees in replicated transects over two seasons to determine the effect of distance from colony when using large placements of colonies (~120 colonies, N = 581 trees), and effect of colony density when using smaller placements of colonies (N = 313 trees). 3. Flowers near colonies maintained an approximately constant mean pollen load over the course of the day, indicating that the rate of pollen released by flowers was matched by the rate of pollen collection by bees. Flowers far from colonies increased in pollen load over the course of the day, indicating relatively less pollen-collecting activity, so that by 15:30 h they had, on average, 46% more than flowers near colonies. 4. Fruit set declined with distance by 22% over 850 m, consistent with the observation that pollen foraging declines over distance from colony. Fruit set also declined with colony density from 46% at 6Á8 colonies per ha to 33% at 2Á8 colonies per ha. 5. Synthesis and applications. Pollen-collecting activity is relatively low at flowers far from honeybee colonies, creating a risk of lost yield through underpollination. Fruit set declines if colony density is reduced below 6Á8 colonies per ha. Pollination outcomes in terms of fruit set are improved when fewer colonies are used per placement (<100) and placements of colonies are arranged with shorter distances (<700 m) between them, so that more trees are within 400 m of colonies.

Relationships between Nut Size, Kernel Quality, Nutritional Composition and Levels of Outcrossing in Three Macadamia Cultivars

“…However, macadamia flowers are bee-pollinated [36,38,[40][41][42][43]45,98] and we have demonstrated that nut production is almost totally reliant on the transfer of pollen from one cultivar to another. Therefore, there is the potential for yield to decline with increasing distance from bee hives [104][105][106] or with increasing distance from another cultivar, as found previously in a 27-row block of "A16" trees [40,47].…”

Massively Introduced Managed Species and Their Consequences for Plant–Pollinator Interactions

“…This translates into important fluxes of pollinators into agricultural and adjacent seminatural habitats during the flowering season of crops (Box 3). Globally, these managed pollinator species represent around 20 species among all social and solitary bee species (Stout and Morales, 2009 A. mellifera is used for honey production and to pollinate MFC such as almonds (Cunningham et al, 2016), mango (Geslin et al, 2016c), apples (Ramírez and Davenport, 2013), pears (Stern et al, 2004) and many others (Garibaldi et al, 2013(Garibaldi et al, , 2016. Contrary to other Apis species that are restricted to Asia, a the native geographical range of A. mellifera spans from Scandinavia to Central Asia and the African continent (Ruttner, 1988;Seeley, 1985;Sheppard and Meixner, 2003).…”

“…To compensate for the losses of wild pollinators, or lack thereof in intensively managed farmland areas, modern agricultural practices usually rely on massively introduced managed pollinators (mainly Apis mellifera and Bombus spp.) that sometimes become the unique pollinating species of the targeted crops (Cunningham et al, 2016).…”

Wild pollinator activities negatively related to honey bee colony densities in urban context

“…For honey bees, we did not detect any increase in their visitation rate with honey bee colony density within 1000 meter buffers. Honey bee foraging range seems to be highly context dependent, from several hundred meters to several kilometers [44,45]. Additionally, Couvillon et al 2015 demonstrated that honey bee foraging distances both depend on the type of rewards that honey bees seek (nectar or pollen) and on the month considered [46].…”