Hosts or Prey
Grape leaffolder and certain other caterpillars
Identification
The presence of H. cushmani or its relatives is recognizable because the parasitoid feeds attached to the outside of host caterpillars. After killing their host the pupae of the wasp occur in silken, white cocoons found near the shriveled body of the caterpillar that they consumed and killed. If grape leaves chewed, scraped, and rolled by a grape leaffolder are present, opening several of the rolled leaves can expose the parasitoid on or near to its host.
The adults are wasps with a narrow waist and a body 1/8 inch (3 mm) long or less. The head, thorax, and front of the abdomen are mostly dark brown. Most of the abdomen is yellowish orange. Adults have long antennae with 25 segments and the abdomen is longer than the head and thorax combined.
Eggs are about 1/50 inch (0.5 mm) long, narrow, and white. They occur attached to the outside of host larvae. The maggotlike Habrobracon larvae are pale orangish or whitish with distinct segments. Mature larvae and pupal cocoons are about 1/8 inch (3 mm) long.
Life Cycle
Habrobracon develops through four life stages: egg, larva, pupa, and adult. Adult females sting and paralyze third instar and older caterpillars. The female then lays one to several eggs on the caterpillar's body. Each parasitoid larva develops through four increasingly larger instars while feeding on the body of a caterpillar that becomes increasingly smaller and shriveled.
The parasitoids per host average about 8 but range from 1 to 20 depending on the size of the parasitized caterpillar. The adult female wasp lays more eggs on larger hosts.
Commonly 30 to 40% of the grape leaffolders in a vineyard are parasitized by H. cushmani, but the percentage parasitism is sometimes higher. During years when grape leaffolders are abundant thousands of adult wasps may be observed flying around vines seeking mates and hosts.
Egg to reproductive adult development occurs in about 2 weeks when temperatures are warm. Habrobracon cushmani has multiple generations per year.
Habitat
Habrobracon cushmani can occur wherever its hosts occur. It is the most commonly observed larval parasitoid of grape leaffolder. The abundance of H. cushmani usually increases as the summer progresses. The parasitoid frequently reduces the abundance of the second and third generations of leaffolders so effectively that the caterpillar is no longer a pest.
Two tachinid flies, Erynnia tortricis and Nemorilla pyste, also commonly parasitize larvae of grape leaffolder. Females deposit one to several oval, white eggs on the head or thorax of grape leaffolder larvae. Two other wasp parasitoids of grape leaffolder pupae are occasionally present, Brachymeria ovata and Pimpla (=Coccygomimus) sanguinipes. Grape leaffolder eggs are parasitized and blackened by Trichogramma species, but their percentage of parasitism is low and apparently unimportant in the control of grape leaffolder.
To improve the effectives of biological control
- Control ants because they attack natural enemies of various grape pests.
- Grow flowering insectary plants to provide nectar and pollen to nourish adult natural enemies.
- Reduce dustiness that disrupts the activities of natural enemies (e.g., periodically hose off small plants or irrigate overhead).
- Avoid the application of broad-spectrum, persistent insecticides for all pests because they are toxic to natural enemies. For example, apply Bacillus thuringiensis to control grape leaffolder and other caterpillars.
For more information see Protecting Natural Enemies and Pollinators and Relative Toxicities of Insecticides and Miticides Used in Grapes to Natural Enemies and Honey Bees.
Species
Habrobracon cushmani is 1 of at least 100 species in the Bracon or Habrobracon genera that occur in the United States. In addition to grape leaffolder, H. cushmani parasitizes at least 10 other species of caterpillars including the Nantucket pine tip moth.
More Information
- Catalog of Hymenoptera in America North of Mexico. Vol. 1: Symphyta and Apocrita (Parasitica), U.S. Department of Agriculture
- Grape Pest Management, Third Edition, UC Agriculture and Natural Resources
- How to Maximize Biological Control in Lodi Vineyards, Lodi Winegrape Commission
- Braconid Parasitoids (Hymenoptera: Braconidae) of Nearctic Choristoneura Species (Lepidoptera: Tortricidae), With a Summary of Other Parasitoid Families Attacking Choristoneura, Canadian Entomologist
Scientific classification:
- Phylum: Arthropoda
- Class: Insecta
- Order: Hymenoptera
- Family: Braconidae
