Managing alternative pollinators through understory management in Wisconsin apple orchards

Background/Question/Methods

The majority of flowering plants, including crop plants, require insect pollination. Bees are the most important pollinators and for many crops, wild bees are more efficient pollinators than managed honey bees. Despite this, modern agricultural practices are often incompatible with the resource requirements of wild bees, leading to a dependence on managed honey bees for pollination. One way in which growers could alter their management strategies to promote wild bees is to provide a diversity of local floral resources on their farms. It is possible, however, that non-crop floral resources could attract bees away from the crop flowers thereby reducing crop yields. The objective of this study was to determine whether the presence of non-crop flowers in the orchard during bloom positively or negatively influenced bee visitation to apple blossoms and the resulting fruit set. We were additionally interested in whether this pattern changed depending on surrounding landscape diversity . To address our objective, we measured bee visitation rates and fruit set at 19 apple orchards located across a wide gradient of landscape diversity in southern Wisconsin. Each orchard had a mowed block, where understory flowers were absent, and an un-mowed block where understory flowers were present.

Results/Conclusions

Preliminary results show that visitation rates to apple blossoms by honey bees, wild bees, and non-bee insects did not vary between mowed and unmowed treatment blocks (honey bee R² = 0.94, p = 0.49; wild bee R² = 0.24, p = 0.82; non-bee insects R² = 0.88, p = 0.72). Moveover, fruit set did not differ between mowed and unmowed treatment blocks (treatment R² = 0.97, p = 0.70). Neither bee visitation rate nor fruit set varied as a function of landscape diversity (treatment x landscape, total visitation R² = 0.92, p = 0.38; fruit set R² = 0.97, p = 0.82). These results suggest that growers do not need to worry about fruit set being negatively effected by non-crop flowers in the orchard during apple bloom. Rather, growers may be able to manage land to protect and enhance wild pollinators, while achieving yield goals as well as conservation targets simultaneously, thereby providing a safety net for pollination into the future.