Feeding potential of adult Systena frontalis (Coleoptera: Chrysomelidae) on leaves of Hydrangea paniculata (Cornales: Hydrangeaceae)

Systena frontalis (F.) (Coleoptera: Chrysomelidae), also known as the red-headed flea beetle, is a defoliating pest of a variety of crop systems, such as ornamentals and food crops. Leaf consumption by this beetle renders ornamental nursery plants, such as hydrangeas (Hydrangea paniculata Siebold, Hydrangeaceae), unsaleable. In Virginia, this insect has become a major pest at commercial nurseries, and their feeding potential on affected crops has not been quantified. In this study, the extent of their damage to individual leaves and host preference between leaf ages were determined. The rate of defoliation on mature and young hydrangea leaves was measured over 24 and 48 h and between different numbers of adults. A single adult caused up to 10% damage to a young leaf or 5% to a whole mature leaf in 24 h. Without choice, there was a higher percent damage to young leaves. When the size of leaves was controlled by cut-out mature leaves, the area damaged was still higher in young leaves when compared with mature leaves. Adult feeding between mature or young leaves was further investigated by choice assays on a caged plant and within a containerized system. In these choice assays, adults inflicted higher percent damage on mature leaves in both caged plant assays and containerized direct choice assays. The choice assays were more similar to field conditions than the nonchoice assays. This demonstrates that S. frontalis showed a preference for mature leaves over young leaves within hydrangeas.