The pollination biology of Haskap (Lonicera caerulea L.: Caprifoliaceae): floral traits and pollinator performance of a new Saskatchewan fruit crop.

Abstract

Haskap (Lonicera caerulea L.) is an early flowering fruiting shrub native to northern regions of Europe, Asia and North America. Commercial growth began in Europe and Asia over a century ago, but it has only recently been cultivated in North America. It is self-incompatible, and requires insect pollinators in order to set fruit; however, very little is currently known about its pollination biology, including associated pollinators and important floral characteristics. My research compared the pollinating performance of three groups of bees on Haskap: commercial Apis mellifera and Osmia lignaria, and wild Bombus spp. I found that Bombus queens had the highest levels of single visit pollen deposition (SVD), the highest visitation rate, and were observed to be active even during cooler temperatures experienced during Haskap flowering. Apis mellifera workers had the lowest levels of SVD, spent nearly three times as long per flower as Bombus spp., and were not active during cooler temperatures; however, as they were present in much higher densities than Bombus, they may be effective in supplementing pollination in pollinator-scarce environments. Osmia lignaria females were found to have potentially high levels of SVD and intermediate visitation rates, however, pollen load analysis suggests they prefer alternative forage and are not frequent visitors to Haskap in field conditions. In addition to pollinator performance, I describe anthesis length, nectar and pollen dynamics, and stigma receptivity in Haskap flowers. I observed that un-pollinated flowers bloomed for 3-4 days, but pollination triggered early senescence. Nectar was present at the onset of anthesis and did not increase significantly after 16 hours, and any nectar removed during anthesis was replaced. There was no evidence of nectar resorption. Pollen release began immediately after the flower opened and continued over the first day, and the stigma showed evidence of receptivity while still in the bud stage. These results suggest that Haskap flowers exhibit a generalist pollination strategy that optimizes pollination opportunities in pollinator scarce environments. Observations that some flowers open in the evening (and possibly overnight) suggest that nocturnal pollinators such as moths may be important for the crop, in addition to known diurnal pollinators.