Grapeleaf Skeletonizer: What You Need to Know

The Grapeleaf Skeletonizer is a moth species that can be a major problem for grape growers and gardeners. It's native to Asia but has been introduced to the United States.

This moth has a distinctive life cycle, with four stages: egg, larva, pupa, and adult. The larvae are the most destructive stage, feeding on grape leaves and causing damage.

The Grapeleaf Skeletonizer's larvae can eat through a significant portion of a grapevine's leaves, leading to reduced fruit production and vine health.

The Grapeleaf skeletonizer is a type of moth.

It has metallic bluish or greenish black wings and a body length of about 0.6 inch.

The wingspan of this moth is 1 to 1.3 inches.

There are three generations per year in the Central Valley and two generations in the cooler coastal regions.

Adult moths of the first generation in the Central Valley emerge from hibernating pupa in early spring to June.

The eggs are pale yellow or whitish, and capsule-shaped, laid in clusters on the underside of grape leaves.

The larvae are up to 0.6 inch long, with five stages of development, and have conspicuous tufts of long black poisonous spines.

On a similar theme: Black Locust Beetle

The life cycle of the grapeleaf skeletonizer is quite fascinating. In California's Central Valley, adult moths of the first generation emerge from overwintering pupae in April and May.

Adult females lay first-generation eggs that along with young larvae are present in late April through June. The larvae develop through five increasingly larger instars.

In the Central Valley, western grapeleaf skeletonizer has 3 generations per year, while in the cooler coastal regions, there are 2 generations. The development time from egg to reproductive adult is about 2 months.

The pupa is brown and lasts about two weeks in the summer, when multiple generations are possible. It's also the overwintering stage, where the pupae are found among leaves at the base of the food plant.

Here's a breakdown of the life stages of the western grapeleaf skeletonizer:

The larvae of the second generation are present in July and August, and those of the third generation in September and October.

Grapeleaf skeletonizer larvae can completely defoliate a grapevine by July, leaving only the larger veins and making the vine more susceptible to disease. This can cause fruit to become sunburned and atypically soft.

Defoliation can also weaken vines and reduce fruit yield. Extensive defoliation is a significant problem for grape growers.

The larvae's hairs exude a stinging chemical that irritates the skin when the caterpillars are contacted, making them a problem for people who handle infested grapevines.

Here are some signs of a grapeleaf skeletonizer infestation:

Some natural enemies of western grapeleaf skeletonizer larvae include parasitoids like Apanteles harrisinae and Ametadoria misella. These parasitoids can help control the population of grapeleaf skeletonizer larvae.

Biological control methods have shown excellent success in managing western grapeleaf skeletonizer populations. Two insect parasites, Apanteles harrisinae and Ametadoria misella, attack larvae in the San Joaquin Valley.

Thousands of these parasites have been released in the area, and Ametadoria misella is now common in many vineyards. This natural method helps keep the pest population under control without harming the environment.

A granulosis virus has also been introduced in selected areas, and it's extremely infectious when introduced to an outbreak population. Symptoms of infected populations include scattered eggs, reduced egg numbers, and larvae that consume tiny patches of tissue.

Diseased larvae are sluggish, feed solitarily, and tend to wander irregularly, leaving a visible trail of liquid excrement. This virus is transmitted from one generation to the next by disease-carrying adults that survive a low degree of infection in the larval stage.

The granulosis virus has been shown to be effective in reducing western grapeleaf skeletonizer populations, making it a valuable tool in integrated pest management.