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Trissolcus basalis
(Hymenoptera: Scelionidae)

The egg parasitoid Trissolcus basalis has been present in the southern U.S. for many decades. It is known worldwide because of its importance as a parasitoid of the southern green stinkbug, Nezara viridula.

Appearance

Minute black wasp with downward elbowed antennae and flattened abdomen. Wing veins are not obvious.

Habitat (Crops)

T. basalis most likely occurs in all crops attacked by southern green stinkbug including cotton, grains, soybeans and other legumes, tomatoes and other solanaceous crops, sweet corn, sunflower, cole crops, cucurbits, fruit and nut crops.

Pests Attacked

The primary host of T. basalis is the southern green stinkbug. T. basalis also attacks the eggs of other species of stinkbugs.

Life Cycle

T. basalis adults mate immediately after emerging from host eggs. The female typically inserts one egg into a host egg. Heaviest parasitoid egg production occurs during the first few days after emergence, then tapers off. The average number of eggs produced per female was 230-300 in one laboratory study. Adults emerge from the host eggs in 9 to 12 days. The life-cycle averages about 23 days at 22°C.

Relative Effectiveness

Southern green stinkbug was accidentally introduced into Australia in 1916, New Zealand in 1944, and Hawaii in 1961. T. basalis has long been considered to be effective at controlling southern green stinkbug in these regions. However, recent studies indicate that control by T. basalis may not be the success previously thought. In addition, T. basalis has not provided consistent control of southern green stinkbug on soybeans in the southern United States.

Strains of T. basalis from Italy, Spain, and France were introduced into California in 1987 and field research showed that 87% of the eggs per mass and 80% of all southern green stinkbug egg masses examined by researchers were parasitized by T. basalis. T. basalis disperses and reproduces well, it parasitizes other stinkbug species when its preferred host is not available, and it is not known to be subject to hyperparasitism or pathogens in North America. T. basalis has a high female to male ratio (up to 5:1) which increases its effectiveness as a parasitoid.

Pesticide Susceptibility

In field trials, T. basalis was little affected by applications of permethrin, but was susceptible to methyl parathion, especially within the first six hours. The methyl parathion also killed some wasps as they exited the host eggs, probably from spray residue on the egg exterior being ingested as they chewed through.

Conservation

Follow the IPM guidelines as outlined in the tutorial of this guide. A nectar source is helpful to other scelionid wasps and may also provide nourishment for T. basalis.

Commercial Availability

T. basalis is not commercially available in North America at this time.

Acknowledgment

Thanks to Walker A. Jones, USDA Agricultural Research Service, Weslaco, TX, for reviewing and making suggestions that have improved this section.

References

Awan, M.S., Wilson, L.T., and Hoffmann, M.P. (1990) Comparative biology of three geographic populations of Trissolcus basalis (Hymenoptera: Scelionidae). Environ. Entomol., 19: 387-392.

Clarke, A.R., Walter, G.H. (1990) Trissolcus basalis as a biological control agent of Nezara viridula in south east Queensland. Proc. 6th Australian Soybean Res. Workshop: 71-73. Brisbane, Queensland, Australia.

Clausen, C.P. (Ed.) (1978) Introduced Parasites and Predators of Arthropod Pests and Weeds: A World Review. (Clausen, C.P., Ed.) Agriculture Handbook No. 480, USDA Agricultural Research Service, Washington, D.C.

Habeck, D.H., Bennett, F.D., and Frank, J.H. (eds.) (1990) Classical Biological Control in the Southern United States. Southern Cooperative Series Bull. No. 355. University of Florida, Gainesville, FL. 197 pp.

Hoffmann, M.P., Davidson, N.A., Wilson, L.T., Ehler, L.E., Jones, W.A., and Zalom, F.G. (1991) Imported wasp helps control southern green stink bug. California Agric., 45: 20-22. Orr, D.B. (1988) Scelionid wasps as biological control agents: a review. Fl. Entomol., 71: 506-528.

Orr, D.B., Boethel, D.J., and Layton, M.B. (1989) Effects of insecticide applications in soybeans on Trissolcus basalis (Hymenoptera: Scelionidae). J. Econ. Entomol., 82: 1078-1084.

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