Transmission of Impatiens Necrotic Spot Virus in Peppermint by Western Flower Thrips (Thysanoptera: Thripidae)

Western flower thrips, Frankliniella occidentalis (Pergande), can transmit a begonia isolate of impatiens necrotic spot virus (INSV) to peppermint, Mentha piperita L. ‘Black Mitcham’. Transmission efficiency for adult thrips 2, 4, 6, 8, and 10 d after emergence varied from 0 to 60% for pairs of thrips and 0 to 20% for single thrips. However, 2-d-old adult thrips failed to transmit the virus. Symptoms of INSV infection of peppermint include stunting, downward curling and leaf tip dieback, and occasional growing tip necrosis. Older leaves are bronze-colored and exhibit sunken, brownish-grey lesions. Symptoms of the original INSV infection found in 1990 in greenhouse-grown ‘Black Mitcham’ cuttings included bright yellow mottling on newly mature leaves. The thripstransmitted isolate of INSV acquired from begonia produced only faint yellow mottling in peppermint leaves when exposed to cool temperatures (15°C). INSV infections were confirmed by symptomology and ELISA analysis. Spherical particles and granular arrays previously associated with INSV infection were observed in some tissue by examination with transmission electron microscopy. Virus was detected throughout the plant indicating a systemic infection. INSV was also detected in the vector thrips by ELISA.