Hosts or Prey
Eggs of consperse stink bug, southern green stink bug, and certain other stink bugs
Identification
The presence of these tiny wasps or related species can be recognized by a change in the appearance of parasitized host eggs. Eggs of most pest stink bugs are relatively pale colored. When parasitized by a Trissolcus species the egg shells darken. When an adult parasitoid emergences it chews a somewhat irregular, rough-edged hole in the egg shell that commonly remains darkened. When a stink bug emerges the egg shell is commonly pale colored, has a smooth-edged, round hole, and the egg's top cap that the emerging stink bug nymph opened may remain partly attached (hinged) to the shell.
Adult Trissolcus are mostly black, stout wasps about 1/16 inch (1.5 mm) long with clear wings. They have brown antennae that are commonly held bent (elbowed) and an abdomen that is flattened on top. Females have brown legs and males have black and brown legs. The eggs, larvae, and pupae occur hidden inside host eggs.
Life Cycle
Trissolcus species develop through four life stages: egg, larva, pupa, and adult. Adults mate immediately after emerging from host eggs. The adult female then inserts one egg into each host egg. If more than one egg is laid in a host the hatching first instars (larvae) fight and only one wasp survives to maturity.
Each adult female lays on average about 200 eggs during her lifetime of about 1 month. Fertilized eggs produce female wasps and unfertilized eggs produce males. After parasitizing an egg mass the female wasp commonly rubs her ovipositor over the eggs. This marks them with a chemical that causes other Trissolcus to recognize the eggs are already parasitized and to avoid them.
Female and male wasps exhibit egg guarding. Females commonly stay with the host eggs until her progeny have become well developed. She chases away other parasitic wasps that approach eggs containing her progeny. Males will also guard a parasitized egg mass. This allows them to mate with young females as soon as they emerge.
Overwintering is as adults in litter on the ground and in other sheltered places. Development time from an egg to a reproductive adult is 2 or 3 weeks when temperatures average 80º and 70ºF, respectively. Trissolcus species have multiple generations per year.
Habitat
Southern green stink bug was first found in California in 1986. It feeds on and damages more than 30 different crops. To provide classical biological control of this pest, the U.S. Department of Agriculture collected its natural enemies in the bug's native range of Europe. Strains of T. basalis from Italy, France, and Spain were sent to California and studied under quarantine. The wasp was then introduced into California during 1987 to 1989. Field research showed that where T. basalis occurs it commonly parasitizes the majority of southern green stink bug egg masses.
Trissolcus species can occur in California anywhere its stink bug hosts occur. The wasp is an important biological control of stink bugs infesting crops including beans, cole crops, cucurbits, fruit and nut trees, and tomato. It can also occur on various weeds.
To improve biological control
- Control ants because they attack natural enemies of various pests.
- Grow flowering insectary plants, such as alyssum that provides adult natural enemies with nectar and pollen as food. The flowering plants for Trissolcus species should be present by early April when the adults become active.
- Reduce dustiness that disrupts the activities of natural enemies (e.g., periodically hose off small plants).
- Avoid the application of broad-spectrum, persistent insecticides for all pests because they are toxic to natural enemies.
For more information see 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 six Trissolcus species occur in California: T. basalis, T. brochymenae, T. euschisti, T. murgantiae, T. podisi, and T. utahensis. All are egg parasitoids of multiple species of stink bugs. In addition to southern green stink bug economically important hosts of T. basalis include conchuela stink bug, harlequin bug, redshouldered stink bug, Say stink bug, and Uhler stink bug.
More Information
- Adult Reproductive Behavior in Ascolcus [Trissolcus] basalis (Hymenoptera: Scelionidae), Australian Journal of Zoology
- Biology of Australian and United States Strains of Trissolcus basalis, a Parasitoid of the Green Vegetable Bug, Nezara viridula, Australian Journal of Ecology
- Catalog of Hymenoptera in America North of Mexico, Vol. 1: Symphyta and Apocrita (Parasitica), Smithsonian Institution Press
- Green Vegetable Bug Egg Parasitoid - Trissolcus basalis, New Zealand Factsheets
- Imported Wasp Helps Control Southern Green Stink Bug, California Agriculture
- Key to Nearctic Species of Trissolcus Ashmead (Hymenoptera, Scelionidae), Natural Enemies of Native and Invasive Stink Bugs (Hemiptera, Pentatomidae), Journal of Hymenoptera Research
- Trissolcus basalis (Hymenoptera: Scelionidae), Cornell University
Scientific classification:
- Phylum: Arthropoda
- Class: Insecta
- Order: Hymenoptera
- Family: Scelionidae
