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Encarsia inaron
(Hymenoptera: Aphelinidae)

by Charles H. Pickett, Biological Control Program, California Department of Food & Agriculture, Sacramento, California

Encarsia inaron is a tiny parasitoid wasp that was collected in Italy and Israel and introduced into California in 1989 for the control of the ash whitefly, Siphoninus phillyreae (Homoptera: Aleyrodidae). Ash whitefly is native to Europe, the Mediterranean, and northern Africa. In both its native home and California it is commonly associated with woody shrubs and trees.

Appearance

Encarsia inaron is a stingless wasp about 0.5 mm in length and difficult to see without a hand lens. Adults appear as minute flies moving about on leaves with whitefly nymphs. Both the adult male and female have dark colored heads and eyes and clear wings, but can be separated by the yellow abdomen of the female and black abdomen of the male. The black pupal case of the parasitoid causes the whitefly nymph to appear black, differentiating it from healthy whitefly pupae that are yellow in color when their wax is removed. The parasitoid pupa chews a round hole upon eclosion to escape from the body of the whitefly. In contrast, healthy whitefly adults push their way out of their pupal case, leaving a "T" shaped split in the whitefly remains.

Habitat

Woody shrubs and trees.

Pests Attacked

Ash whitefly, Siphoninus phillyreae.

Life Cycle

Unlike most species of Encarsia, both male and female E. inaron develop as primary parasitoids on ash whitefly. It is the most common parasitoid associated with ash whitefly in its native home.

Parasitoids oviposit into third and fourth instar whiteflies, and complete their development inside the whitefly host. The developing larvae become banana shaped and translucent in color, inside late instar whitefly nymphs, but can only be seen through dissection and with the aid of a microscope. Parasitoids at 25oC take approximately three weeks to develop from eggs to adults. At the same temperature, adults live two to three weeks, laying about 159 eggs each.

Relative Effectiveness

Prior to the establishment of E. inaron in California, ash whitefly infestations in major urban centers resulted in early season defoliation of street trees such as species of ash and ornamental and flowering pear trees. In some neighborhoods the air was filled with clouds of adult whiteflies. Although some generalist natural enemies fed on these whiteflies, they completely lacked specific parasitoids or predators.

Encarsia inaron was reared in the Biological Control Program of the California Department of Food & Agriculture in Sacramento and at the University of California, Riverside. Within two years of releasing E. inaron, populations of ash whitefly dropped to levels that were difficult to detect. Detailed life table studies demonstrated that this parasitoid alone is responsible for reducing whitefly population densities. The ash whitefly effort provided $219,822,823 and $298,803,970 in aesthetic benefits to California in wholesale and retail landscape tree replacement values, respectively. Savings to cities for not having to manage ash whitefly-infested trees accrue annually into perpetuity.

By 1992 E. inaron had been colonized throughout most of California. As of 1996, ash whitefly continues to be maintained at very low levels and is difficult to find most of the year. Although we have heard some reports of heavily infested trees, these are isolated events. This single introduction is responsible for controlling ash whitefly infesting urban ornamental trees throughout the state and represents classical biological control at its best. Prior to colonization of E. inaron, ash whitefly affected millions of homeowners, and received much media coverage. Today, ash whitefly is difficult to find.

Conservation

Encarsia inaron has dispersed over wide areas of California, and apparently other parts of the country, wherever ash whitefly has moved. Once established, the parasitoid regulates densities of ash whitefly to very low numbers thus additional control of this pest is in almost all cases unnecessary. The best way to conserve the parasitoid is to avoid pesticide usage in or near trees where E. inaron is present. In the rare case in which ash whitefly may reach high numbers, spraying the foliage repeatedly with water or a soap spray is recommended. The parasitoids overwinter in both the duff of trees and on some evergreen shrubs infested by ash whitefly during winter months, such as citrus, pyracantha and toyon. Maintaining fallen leaves at the base of deciduous trees susceptible to ash whitefly (ash and ornamental pear trees) or planting the above shrubs nearby may provide increased continuity in the parasitoid's presence.

Commercial Availability

Not available commercially.

References

Driestadt, S. H. & Flint F. L. 1995. Ash whitefly (Homoptera: Aleyrodidae) overwintering and biological control by Encarsia inaron (Hymenoptera: Aphelinidae) in northern California. Environ. Entomol 24: 459-464.

Gould, J. R., Bellows, T. S., and Paine, T. D. 1992. Evaluation of biological control of Siphoninus phillyreae (Haliday) by the parasitoid Encarsia partenopea (Walker), using life-table analysis. Biological Control 2, 257-265

Pickett, C. H., J. C. Ball, K. C. Casanave, K. M. Klonsky, K. M. Jetter, L. G. Bezark, and S. E. Schoenig. 1996. Establishment of the ash whitefly parasitoid Encarsia inaron (Walker) and its economic benefit to ornamental street trees in California. Biological Control 6: 260-272.

Sorensen, J. T., Gill, R. J., Dowell, R. V., and Garrison, R. W. 1990. The introduction of Siphoninus phillyreae (Haliday) (Homoptera: Aleyrodidae) into North America: niche competition, evolution of host plant acceptance, and a prediction of its potential range in the nearctic. Pan-Pacific Entomol. 66, 43-54.

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