How to Manage Pests

Pests in Gardens and Landscapes

Granulosis virus disease

The most effective biological control agent of western grapeleaf skeletonizer is a granulosis virus. This host-specific virus kills eggs, larvae, and pupae. The virus attacks the gut of the larvae, which results in dark diarrhetic blotches on the leaves. Healthy larvae can become infected by virus particles in the excrement. Other insects distribute the virus when they walk through the diarrhetic blotches.

There are four typical symptoms of infection in adults and larvae: 1) eggs are scattered and the number of eggs is reduced, 2) eggs fail to hatch, 3) larvae consume tiny patches of tissue rather than consuming entire areas of the leaf, and 4) larval growth and coloration change and larvae shrink and eventually die.

Infected larvae
Infected larvae are disoriented

Dying larvae
Dying larvae

Scattered eggs
Scattered eggs

Statewide IPM Program, Agriculture and Natural Resources, University of California
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