Spatial and temporal variation in pollinator effectiveness: do unmanaged insects provide consistent pollination services to mass flowering crops?

Abstract

Summary1. Recent declines in honeybee populations have focused attention on the potential for unmanaged insects to replace them as pollinators of food crops. The capacity of unmanaged pollinators to replace services currently provided by honeybees depends on the spatial and temporal variability of these services, but few quantitative assessments currently exist. 2. We investigated spatial variation in pollinator importance by comparing pollinator efficiency and effectiveness in stigmatic pollen loads, stigmatic contact and visitation rate between honeybees and the seven most abundant unmanaged taxa in 2007. We assessed temporal variability in pollinator visitation using floral visits recorded three times a day over four consecutive years (2005)(2006)(2007)(2008) in 43 'Pak Choi' Brassica rapa ssp. chinensis mass flowering fields in the Canterbury region of New Zealand. Further, we compared the aggregate effect of the unmanaged pollinator assemblage to the managed honeybee. 3. Pak Choi was visited by many insect species that vary in abundance and effectiveness as pollen transfer agents. There was spatial variation in the four measures of pollinator importance. Pollen deposited on stigmas and flower visits per minute were not significantly different comparing the unmanaged assemblage to honeybees, although stigmatic contact and visitor abundance per number of open flowers were greater in honeybees. 4. Unmanaged taxa were frequent visitors to the crop in all 4 years. The pooled services provided by the unmanaged assemblage did not differ within a day and were equal to or greater than those provided by honeybees in 2 of the 4 years. Pollinator importance changed little irrespective of the spatial and temporal variations among taxa. 5. Synthesis and applications. The results of this study suggest that some unmanaged insect taxa are capable of providing consistent pollination services over a 4-year period in a commercial mass flowering crop. As these taxa already contribute substantially to the pollination of food crops, they offer a safety net in the case of sudden collapse of managed honeybee hives. To optimize pollination services, we recommend pollinator-specific farm management practices that consider the needs of both managed and unmanaged pollinator taxa.

Weeds for bees? A review

“…Pollination by insects is vital for both crops and wild plants (Ollerton et al 2011): 84 % of European cultivated plants depend on insect pollination (Williams 1994) and 70 % of 57 crops grown worldwide (Klein et al 2007). Wild and honeybees are the main pollinators of these crops (Klein et al 2007;Garibaldi et al 2013;Rader et al 2012), and their pollination service to crops has been valued at 153 billion euros annually worldwide (Gallai et al 2009), and around 22 billion euros annually for Europe (Gallai et al 2009) and more than 18 billion dollars in the USA . A more recent study (Lautenbach et al 2012) of 60 crops suggested 266 billion euros per year worldwide, and an estimated 3-8 % of world crop production could be lost in the absence of pollinators ).…”

Pollination ecosystem services in South African agricultural systems

“…65,103 Canola farmers, growing self-compatible varieties, may benefit from insect pollination which has been shown to increase seed set and seed quality. 70,104,105 In the early 1990s, rain-fed canola production was introduced in the winter rainfall region of the Western Cape and grown in rotation with wheat-barley-lucerne. 106 Canola has rapidly become an integral floral resource for beekeepers, particularly for those beekeepers who provide pollination services, as it allows colonies to build-up their strength prior to crop pollination.…”

Seasonal complementary in pollinators of soft-fruit crops

“…The role of wild pollinators in delivering this service is likely to be 50 greater than was previously assumed: a meta-analysis of pollination data from 41 crop systems 51 suggests that honeybees supplement wild pollinator numbers, rather than the other way around 52 (Garibaldi et al 2013) and wild pollinators play a significant role in varied crop systems (e.g. Winfree 53 et al 2008;Breeze et al 2011;Rader et al 2012). Wild species are also important for their 54 contribution to pollinator diversity, which has been shown to positively influence crop yield (Klein,55 Steffan-Dewenter & Tscharntke 2003).…”