This article was written collaboratively by Anitha Chirumamilla and Ada Szczepaniec.
It is past mid-September and sunflowers are nearing maturity with harvesting dates approaching. Beetles of various sizes are most commonly spotted on sunflowers during this time, and while there may be many of them, they are not considered sunflower pests. There are two beetles that are seen actively feeding on sunflower heads and appear to be of concern to producers while causing no damage to the crop. One of them is the bumble flower beetle (BFB), which belongs to the scarab beetle family. BFB’s are not pests of sunflowers as adults or larva and they do not cause any damage that is of economic concern. Chemical treatment is not recommended or needed for control. BFB’s are bigger in size measuring about ½ to ⅝ inches long, and come in different colors ranging from yellowish brown to dark brown with black spots on their forewings. Body and legs are covered with hairs, and the beetles make a loud buzz resembling that of bumble bees and hence the name BFB. Adults emerge from the overwintering sites in the soil during spring. Larvae are ‘C’ shaped grubs, which feed on the decaying organic matter in the soil and are often mistaken for June beetle larvae (pest of turf grass damaging the roots). Adult beetles feed on pollen and nectar of sunflowers and are attracted to the scent of infected plant tissue damaged by other insects and pathogens. The sight of these beetles feeding on the injured or infected tissue is often misleading, because they are not the cause of original damage.
Sap beetles are another group of beetles that are attracted to smell of secretions from wounded/diseased and ripened plant parts. In contrast to BFB’s, sap beetles are much smaller in size (⅛ to ¼ inch long) and dark colored with orange to yellow spots and bands on their body. They are easily identified by their antennae, which are club shaped (aka, the knobbed antennae), and their short wings exposing the tip of abdomen. Adult beetles overwinter in soil and emerge in spring. Eggs are laid near the vicinity of overripe or decaying plant matter which serve as feeding sites for hatching larvae. Sap beetles are not known to cause any damage in sunflowers, and no treatment is necessary to manage these insects.
Above: Bumble flower beetle feeding on dead tissue of sunflower. Photo credit: Anitha Chirumamilla