Assessing Bee Attractiveness of Woody Landscape Plants and Mitigating Potential Bee Hazard from Neonicotinoid Insecticides

Maintaining bee-friendly habitat and food resources in cities and suburbs can help conserve bees’ vital pollination services to gardens, ornamental landscapes, and native plants in remaining fragments of semi-natural habitat.1-4 With bee populations being imperiled by habitat loss, diseases, parasites, and other stresses5, 6 and public awareness of those problems increasing7 the issue of pollinator health poses new challenges for the horticultural industry. Research based guidelines are needed to help growers and landscape managers manage insect pests without harming bees, and to ensure that plants sold in garden centers are non-hazardous to bees after being transplanted to the landscape. The “bee issue” also offers opportunities for the Green Industry. Interest in backyard wildlife conservation and butterfly gardening is on the rise. The public is increasingly mindful of bees’ pollination services to gardens, wildflowers, and fruit-bearing ornamental trees that provide beauty and interest in landscapes, and food for birds and other desirable urban wildlife.8 Documenting and publicizing ornamentals for bee-friendly landscapes can stimulate sales of such plants. More people have heard about Colony Collapse Disorder and declining native bee populations7, and many of them perceive that pesticides are the cause.9 Land care professionals who offer bee-friendly programs can gain a competitive edge with such customers. Neonicotinoid insecticides are mainstays for protecting ornamental plants from aphids, scale insects, leaf miners, borers, and other insect pests. Applied via soil injection, soil drench, trunk injection, or basal bark spray, they move via the xylem to feeding sites of targeted pests. Systemic treatment reduces much of the hazard to beneficial insects that might occur from whole-plant sprays.10-11A key debate is whether or not neonicotinoid residues translocate to floral resources (pollen and nectar) at high enough concentrations to pose a hazard to bees in field settings, a question that will require field studies with relevant exposure and duration to resolve. Although such hazard probably low, transitory, and manageable12-14 the potential for high doses of neonicotinoids to harm bees was highlighted by a massive, highly publicized bee kill following spraying of flowering trees in violation of label instructions.15 The Green Industry, which supports both environmental stewardship and reasonable pesticide regulations, can ill-afford the fallout from another such incident. Our recent research verified that hazard to bumblebees foraging on flowering weeds in treated lawns can be mitigated by adhering to label precautions, or if blooms are inadvertently contaminated, by mowing to remove them. 4,14 Imidacloprid or clothianidin residues in nectar of directly contaminated white clover blooms averaged about 6000 and 3000 ng/g, respectively, but levels nectar of blooms formed after the first mowing were reduced by > 99.6%. Moreover, urban bees forage on diverse flowering plants1,16 most of which are not treated with systemic pesticides.