Fruit Crops News

Biological Control of Tarnished Plant Bug in Strawberry Production in the Midwest

The tarnished plant bug, Lygus lineolaris, is the key insect pest attacking strawberries in Iowa and other midwestern States. Feeding by nymphs on the developing fruits causes misshaped berries and significantly reduces yields from strawberry plants. Researchers in California have used annual releases of the commercially available wasp egg parasitoid Anaphes iole to reduce tarnished plant bug densities in California strawberry fields. During the 1980's, USDA biological control researchers introduced a European braconid wasp, Peristenus digoneutis, that parasitizes tarnished plant bug nymphs in the Northeastern U.S. Parasitism of tarnished plant bug nymphs by P. digoneutis in the release areas was approximately 30%, which is 3 times the parasitism from native parasitoids.

Will releases of these wasps work in the Midwest for biological control of the tarnished plant bug? Does the use of this type of biological control require an entirely new approach to pest management in strawberries? If a grower decides to use biological control, is it likely that damage due to insects would increase?

These are important questions that need to be addressed before biological control of tarnished plant bug can be recommended in midwestern strawberry fields. No one has answers to these questions yet but researchers at Iowa State University are working on them, and do have a good basis to advise a grower of some of the differences a biologically-based approach to pest management would include.

Reducing the use of insecticides for the tarnished plant bug may have a dramatic effect on the diversity of insects in a strawberry field. Could this result in outbreaks of other insect pests, for example the strawberry leaf roller? Based upon studies done at Iowa State University, it is unlikely that a secondary pest such as the leafroller would become a problem. In a three year study in central Iowa, 14 species of parasitic wasps were recovered from leafroller larvae. Because strawberries have a relatively high tolerance for leaf roller feeding and leaf rolling activities, these naturally-occurring parasitoids should maintain populations at tolerable levels. Reducing insecticide use should also have a positive effect on the abundance of predatory species in a strawberry field, for example, lady beetles and spiders. The transition from an insecticide-based approach to strawberry insect pest management to a biologically-based approach can be accomplished in the Midwest.

The strawberry extension-research group at Iowa State is evaluating the potential of biological control in the Midwest. Individual growers may also wish to experiment with biological control in a portion of their fields to determine if this is a viable approach for pest management on their farm. Although the group can provide evaluations of the benefits and risks of biological control and insecticide-based approaches to insect pest management in strawberry production, individual growers need to decide what is best for their particular situation.

Why should you consider reducing the use of insecticides on strawberries?

- John Obrycki, Iowa State University

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