Hosts or Prey
Eggs of various insects, especially moths
Identification
The most obvious evidence that Trichogramma or related parasitoids are present is that the eggs of hosts that are normally pale colored darken because parasitization of the host changes the pigmentation of its eggshell.
When an adult Trichogramma emerges from a parasitized egg, it leaves a round hole in the egg shell that remains darkened by the parasitism. Tiny, dark pellets of parasitoid feces (meconium) can be visible inside the egg shell. When caterpillars hatch from their egg the emergence hole is generally ragged, the egg shell is empty (contains no meconium), and the shell is commonly pale colored.
Trichogramma are difficult to reliably identify to species due to their minute size and similar appearance. The adults are generally orange to yellowish brown and 1/100 to 1/25 inch (0.25–1 mm) long. The antennae are relatively short. The bulging eyes and tiny, dotlike light receptors on top the head (ocelli) are red. The clear wings are fringed with tiny hairs.
Trichogramma eggs larvae and pupae occur inside host eggs. The eggs are ovoid and about 1/200 inch (0.1 mm) long. The larvae are saclike with mouthparts visible in the late instar. Mature larvae and pupae are about 1/50 inch (0.5 mm) long. Pupae are initially saclike and as they age develop distinct appendages folded against the body.
Life Cycle
Trichogramma species develop through four life stages: egg, larva, pupa, and adult. The adult wasp lays one or more eggs in a recently laid egg of its hosts. After hatching the wasp larvae feed inside on the host embryo. The larvae then pupate inside the egg and the adult wasps chew a hole in the shell and emerge.
Each Trichogramma female can parasitize about 100 host eggs. Additional eggs are killed by the female wasps feeding on them. The wasps host feed by puncturing egg shells with their ovipositor then consuming the oozing contents.
Egg to adult development time is about 7 to 14 days during the growing season. Trichogramma abundance can increase rapidly because these parasitoids commonly have more generations than their hosts.
Trichogramma overwinter as mature larvae in host eggs. In mild winter locations the wasps can be active throughout the year when host eggs are present. Trichogramma species have multiple generations per year.
Habitat
Trichogramma naturally occur in field and tree crops, gardens, landscapes, and wildlands wherever eggs of their insect hosts are found.
Commercial Availability
Trichogramma species are sometimes purchased and released to kill the eggs of pest moths. The wasps are shipped as immatures inside moth eggs glued to small cards that can be attached by hand to infested plants. Reports of successful control from mass releases include Trichogramma platneri to control amorbia in avocado, tomato fruitworm in tomato, and codling moth in walnuts. See Mass Releases of Wasps Can Reduce Damage from Codling Moth for discussion of how Trichogramma can be released.
To increase the effectiveness of resident natural enemies and any that are released
- Avoid the use of broad-spectrum and persistent insecticides for all pests because they are toxic to natural enemies.
- Control ants because they attack natural enemies of various pests.
- Grow flowering plants (insectary plants) that provide nectar and pollen to nourish adult natural enemies.
- Reduce dustiness that disrupts the activities of natural enemies (e.g., irrigate overhead or periodically hose off small plants).
For more information see The Association of Natural Biocontrol Producers, Biological Control Organisms for Insects and Mites (PDF), Natural Enemy Releases for Biological Control of Crop Pests, Protecting Natural Enemies and Pollinators, and the table of relative toxicities of insecticides and miticides to natural enemies and honey bees for specific crops.
Species
At least 29 Trichogramma species occur in California. Trichogramma brassicae, T. minutum, T. platneri, and T. pretiosum are naturally occurring important species that can also be purchased for mass release.
Trichogramma parasitize eggs of hundreds of different species of insects, especially eggs of butterflies and moths, but also those of beetles, flies, true bugs, sawflies, and certain other insects. Some species prefer eggs of certain types of hosts while others prefer certain habitats and can parasitize the eggs of a variety of insects in that environment. Trichogramma platneri for example parasitizes eggs of at least 28 species of moths.
More Information
- Biological Control of Two Avocado Pests, UC Riverside, California Agriculture
- Genus Trichogramma, BugGuide, Iowa State University
- Mass Releases of Trichogramma Wasps Can Reduce Damage from Codling Moth, California Agriculture
- Trichogramma ostriniae Pang et Chen Hymenoptera: Trichogrammatidae, Cornell University
- Trichogrammatids In Ecofriendly Pest Management for Food Security, Elsevier
- Universal Chalcidoidea Database, Natural History Museum of London
Scientific classification:
- Phylum: Arthropoda
- Class: Insecta
- Order: Hymenoptera
- Family: Trichogrammatidae
