The Grapevine Beetle (Pelidnota punctata), often called the Spotted June Beetle, is a large scarab species native to North America. It is commonly found in vineyards, gardens, and wooded areas across the eastern and central United States and Canada. Although its name suggests a severe threat, the beetle is typically considered a minor pest to cultivated grapevines. The impact depends entirely on its life stage, as the adult and larval forms have vastly different diets.
Identifying the Grapevine Beetle
The adult beetle is a substantial insect, typically measuring between one and 1.2 inches long. Its body is colored, ranging from yellowish-orange to reddish-brown or tan. It is defined by a pattern of six black spots, with three dots aligned along the outer edge of each wing cover (elytron).
The adults are most active during the summer, emerging from late June through August. They cling to foliage during the day and are strongly attracted to lights at night. The larval stage, known as a grub, lives underground for most of its two-year life cycle. This pale, fleshy, C-shaped creature can grow up to two inches long.
What the Adults Consume
The adult Grapevine Beetle primarily consumes the leaves of grapevines. This feeding behavior is the main source of visible damage. The beetles use their chewing mouthparts to consume leaf tissue, often resulting in skeletonized leaves with large, irregular holes.
In heavy infestations, the beetles may consume the entire leaf, leaving only the central midrib and major veins. Adults also occasionally feed on ripe fruit, though foliage is preferred. If grapevines are unavailable, they will feed on related plants, such as Virginia Creeper. Fortunately, this defoliation is rarely severe enough to compromise the health or survival of a mature vine.
The Diet of the Larval Stage
The diet of the Grapevine Beetle larva differs significantly from the adult’s. Females lay eggs near decaying organic material, such as rotting logs, tree stumps, and compost. The resulting C-shaped grubs are primarily decomposers, feeding on decaying wood and detritus in the soil.
These grubs are often mistaken for the larvae of other scarab beetles, like Japanese Beetles, which destroy the living roots of turfgrass and garden plants. Unlike those true root pests, the Grapevine Beetle grub is generally beneficial to the soil ecosystem. They aid in the breakdown of woody debris, nourished by the dead tissue of trees like elm, oak, and maple.
Controlling Infestations
Since the damage caused by the adults is usually minor, chemical intervention is often unnecessary. Physical removal is the most practical and effective method for small-scale vineyards and home gardens. The beetles are large and somewhat clumsy, making them easy targets for hand-picking.
Because the adults are sluggish in the early morning and late evening, these times are best for checking the vines. Simply knocking the beetles off the foliage and into a container of soapy water provides a quick, non-toxic control measure. Cultural practices, such as removing old tree stumps and decaying wood debris from the vicinity of the grapevines, can also reduce populations. This sanitation eliminates the preferred egg-laying sites, interrupting the insect’s two-year life cycle.