Overview
Lined June beetles are beetles whose larvae, known as grubs, feed on plant roots. The adult beetles may also feed on foliage. Root feeding is the most damaging stage, often affecting lawns and crops.
The Western Giant: Lined June Beetles
The Lined June Beetle (Polyphylla decemlineata), also known as the Ten-Lined June Beetle, is one of the most striking and largest scarab beetles found in western North America. Reaching up to 35mm in length, these beetles are easily identified by the four long white stripes and one short stripe on each of their wing covers (elytra), set against a dark brown or black background. In the summer evenings across the West, they are frequently seen clumsily buzzing around porch lights.
Life Cycle and Underground Destruction
While the adult beetles are highly visible, the majority of their life cycle is spent underground as larvae. These “white grubs” are massive, C-shaped, and can live in the soil for two to four years before pupating. During this time, they are formidable subterranean pests:
- Root Consumption: The larvae feed voraciously on the roots of various plants, including fruit trees (apple, peach), berries, and ornamental shrubs.
- Vascular Damage: By destroying the root system, they prevent the plant from taking up water, leading to “sudden” wilting and death, especially in younger trees.
- Soil Disturbance: Their large size and movement can physically disrupt the soil structure around sensitive root balls.
Identification and Unique Behaviors
If you encounter a Lined June Beetle, you may notice two distinct features. First, the males have spectacular, oversized fan-like antennae, which they use to “sniff” out pheromones from females. Second, if handled or threatened, these beetles produce a loud, startling hissing sound. This isn’t a vocalization, but rather a result of the beetle rubbing its abdomen against its wing covers (stridulation).
Management
Control is difficult because the larvae are buried deep in the soil and the adults are highly mobile. In home landscapes, light management is the easiest preventative measure—turning off outdoor lights during their mid-summer flight period reduces the number of females attracted to your property to lay eggs. For severe infestations in orchards, tilling the soil can expose the large grubs to birds and other predators, though this must be done carefully to avoid further damaging the tree roots.
These pests are closely related to other soil-dwelling insects and are part of the Pest Directory.
Damage
- Root damage
- Wilting plants
- Dead patches in lawns
Management
- Monitor soil for grubs
- Use biological controls
- Maintain healthy turf