Willow trees, and some other species, can be buzzing with wasps, bees, flies, and other insects during late summer. The winged visitors are attracted to the sugars in honeydew excretions from sap-feeders, such as aphids or soft scales.
Eliminating the sap feeders should be an effective way to make the bees, etc. go elsewhere. However, their control requires thorough spray coverage with a contact insecticide, such as insecticidal soap. This is difficult to achieve on medium to large trees and could kill some beneficial insects. In addition, the honeydew deposits will remain until removed by rains and weathering. It often is best to avoid the area while stinging insects are present, rather than making insecticide applications that could do more harm than good.
By Lee Townsend, Extension Entomologist