Population Dynamics and Feeding Preferences of Thrips ( Thysanoptera : Thripidae ) as Tospovirus Vectors in North Carolina Cut Flower Production

SUTLIFF-SHIPLEY, SUSAN G. Population Dynamics and Feeding Preferences of Thrips (Thysanoptera: Thripidae) as Tospovirus Vectors in North Carolina Cut Flower Production. (Under the direction of Dr. Christine A. Casey). Many cut flower crops are susceptible to both of impatiens necrotic spot virus (INSV) and tomato spotted wilt virus (TSWV) which are commonly vectored by Frankliniella fusca (Hinds) and F. occidentalis (Pergande) (Thysanoptera: Thripidae) in North Carolina. INSV and TSWV are among the most damaging plant diseases affecting the floriculture industry. Thrips were surveyed in field cut flower production in eight field locations across North Carolina during the 2005 growing season to determine regional and production differences in thrips species distribution and abundance. Thrips populations were monitored via yellow sticky traps and by directly sampling the blooms of 20 common floral crop species and 11 surrounding weed species. F. tritici (Fitch) was the most common thrips species overall and the most common virus vector was F. fusca. Relatively low numbers of F. occidentalis and Thrips tabaci (Lindeman), another reported vector, were also collected. The spatial and temporal occurrence of vector species varied regionally, but there were no significant differences in vector populations between conventional and organic production systems. There was a positive correlation between thrips sampled on sticky traps and thrips sampled directly on floral blooms. Weed species Triodanis perfoliata, Ranunculus spp. , Oxalis spp. , Taraxacum officinale, and Trifolium incarnatum and crop species Centaurea cyanus, Chysanthemum spp. , Antirrhinum majus, Achillea millefolium, Matricaria recutita, and Lilium Asiatic hybrid consistently supported the largest populations of adult TSWV vector species. F. fusca, was the most abundant TSWV vector species collected, comprising over 95% of vector species in the Piedmont region and 98% in the Coastal Plain region. The results of this study demonstrate the relative potential of cut flower crops and weed plants to act as important reproductive sites for F. fusca and F. occidentalis as innoculum sources of TSWV and INSV. Differences in seasonal patterns and within plant distribution should be considered in developing sampling protocols and management plans for tospovirus vectors. F. occidentalis is one of the most efficient vectors of INSV and TSWV in greenhouse production. Indicator plants, which develop virus symptoms faster than crop plants, are a potential tool for detection of viruliferous thrips. If thrips do not prefer to feed on these relative to crop plants, their utility as indicators may be limited. Two accepted indicator plants, petunia and fava bean, were evaluated in a F. occidentalis feeding preference choice tests. Petunia leaves had significantly more feeding scars per cm2 than fava bean leaves, suggesting that thrips will feed preferentially on petunia. The two indicator plants were also compared with important greenhouse crops in a thrips feeding preference choice test. Crop plants included: garden impatiens, New Guinea impatiens, gloxinia, begonia, kalanchoe, and chrysanthemum. Petunia leaves had significantly more feeding scars per cm2 than the other plant species tested, suggesting that thrips will feed preferentially on petunia relative to other crop plants and thus, will be useful as a virus indicator. Six petunia varieties, ‘Purple Wave’, ‘White Bedder’, ‘White Swan’, ‘Red Halo’, ‘Dreams–Midnight Blue’, and ‘Mix’ (heirloom) petunia were also evaluated in a thrips feeding preference choice test. Feeding preference tests with non-viruliferous thrips showed that the varieties ‘Mix’ and ‘Red Halo’ had significantly more feeding scars than any other variety. Choice feeding tests using thrips infected with TSWV using the same petunia varieties were inconclusive. However, only the varieties ‘Purple Wave’, ‘Mix’ and ‘White Bedder’ showed characteristic necrotic lesions indicative of TSWV infection and presence of viral lesions suggest that these varieties may be more suitable as tospovirus indicator plants. POPULATION DYNAMICS AND FEEDING PREFERENCES OF THRIPS (THYSANOPTERA: THRIPIDAE) AS TOSPOVIRUS VECTORS IN NORTH CAROLINA CUT FLOWER PRODUCTION By SUSAN G. SUTLIFF-SHIPLEY A thesis submitted to the Graduate Faculty of North Carolina State University in partial fulfillment of the requirements for the degree of Master of Science ENTOMOLOGY Raleigh, NC 2006