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Western Flower Thrips

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Progress Report - 1991

Ralph E. Berry, Department of Entomology, Oregon State University, Corvallis, OR

Note: this information is considered unpublished work and should not be used as final or finished results. It has been included in IPMP 3.0 because it may not be available from other sources, and in some cases may include information that may not reach final publication.

Survey for thrips in mint, vectors of TSWV in Mint

In 1990, it was confirmed that peppermint is susceptible to tomato spoted wilt virus (TSWV) and Impatiens Necrotic Spot Virus (INSV).  In 1991, research indicated that these viruses are transmitted by western flower thrips and onion thrips. Even though the economic impact of this virus in commercial peppermint is unknown, it is important to know whether or not thrips vectors occin in peppermint fields.

We surveyed peppermint fields in 1991 in western and central Oregon to determine the incidence of thrips in peppermint. Two yellow sticky traps were placed in each of nine fields in western and central Oregon (18 total traps in each production area). In central Oregon, the thrips survey was conducted in cooperation with Mr. Steve James, Central Oregon Agricultural Research Center in Madras. Traps were placed in peppermint fields in mid-June and removed before harvest in mid-August.

Results of this survey indicated that thrips (western flower thrips) were very abundant in peppermint fields during the growing season, which suggests that the potential for spread of TSWV is high.  However, we did not determine whether or not the thrips collected on the traps were infected with TSWV and cannot say for certain that the incidence of TSWV increases in peppermint fields during the summer. A detailed study of the vector/virus relationships in peppermint must be conducted before the economic impact of TSWV on commerical peppermint is known.

Diane Sether, a graduate student in Entomology, confirmed that western flower thrips can successfully transmit TSWV to peppermint.   She fould that TSWV is ingested by nymps but is transmitted to peppermint only by adult thrips, greater than two days old.  She described the general symptomology of TSWV infection of peppermint as follows: stunting and downword curling of leaves occasinally accompanied by tip necrosis, older leaves occasionally with sunken, brownish-gray lesions and a bronzy appearance, yellow mottling on leaves which may become more evident under cool temperature conditions.  ELISA (enzyme-linked immunosorbent assay) detection of virus throught the plant indicates the infection is systemic.