ARTHROPODS IN RELATION TO PLANT DISEASE Effect of Host Plant Tissue on the Vector Transmission of Grapevine Leafroll-Associated Virus 3 CHI-WEI TSAI, 1,2 DOMENICO BOSCO, 3 KENT M. DAANE, 4 AND RODRIGO P. P. ALMEIDA 4 J. Econ. Entomol. 104(5): 1480Ð1485 (2011); DOI: http://dx.doi.org/10.1603/EC10412 ABSTRACT Many biotic and abiotic factors affect the transmission efÞciency of vector-borne plant pathogens. Insect vector within-plant distribution and host tissue preference are known to affect pathogen acquisition and inoculation rates. In this study, we Þrst investigated whether feeding tissue affects the transmission of Grapevine leafroll-associated virus 3 by Planococcus ficus (Signoret) (Hemiptera: Pseudococcidae) and the effect of mealybug within-plant distribution on virus trans- mission under greenhouse conditions. Results showed no signiÞcant effect on transmission efÞciency after insect conÞnement on leaf blades, petioles or stems of virus source or healthy test plants for either acquisition or inoculation trials. Transmission efÞciency of a single mealybug varied from 4 to 25% in those trials. Second, we tested whether leaf position affected transmission efÞciency due to potentially variable virus populations within acquisition plant tissues. No signiÞcant differences of transmission rate among acquisition leaf position were observed, probably because there were no differences in the virus population within source tissues. Finally, we examined the seasonality of the virus in Þeld-collected samples and found that GLRaV-3 prevalence varied along a growing season, such that GLRaV-3 translocated along expanding shoots to leaves. Similarly, mealybug populations are known to increase in spring, and then mealybugs spread to cordons and leaves. This coordination of spatial and temporal dynamics of the virus and its vector may increase the risk of GLRaV-3 transmission during late spring and early summer. Further integration of information about pathogen populations in plants, vector feeding behavior and vector population seasonality could lead to more effective management practices. KEY WORDS Ampelovirus, Closteroviridae, Planococcus ficus, semipersistent The transmission ecology of vector-borne plant patho- gens is mediated by a complex network of interactions that connect host plant, insect vector and pathogen. Vector feeding behavior, host tissue preference and within-plant distribution may affect the transmission efÞciency of pathogens at the level of plantÐinsect interactions (Fereres and Moreno 2009). Differences in probing behavior can lead to variability in the trans- mission of nonpersistently transmitted viruses (Wang and Ghabrial 2002, Fernandez-Calvino et al. 2006, Pel- letier et al. 2008). Insect vectors also may be unevenly distributed within plants, preferring to colonize spe- ciÞc host tissues with higher or lower pathogen pop- ulations, which can be positively correlated to acqui- sition efÞciency and subsequent changes in disease spread (Marucci et al. 2004, Daugherty et al. 2010). Host physiological condition and environmental fac- tors also inßuence host tissue feeding preference of vectors (Elliott and Hodgson 1996, Tsai et al. 2002, Srinivasan and Alvarez 2007). It is therefore not sur- prising that a wide range of biological and physical factors have been shown to affect pathogen transmis- sion efÞciency. However, the integration of informa- tion on vector host tissue preference in relation to pathogen within-plant distribution and its conse- quences to transmission ecology and disease spread has not been widely performed. Grapevine leafroll disease occurs in all major grape (Vitis spp.)-growing regions worldwide and is one of the most destructive viral diseases of grapevines. The disease is associated with many distinct closterovi- ruses sequentially named grapevine leafroll-associ- ated viruses (GLRaV-1, -2, -3, and so on; Martelli et al. 2002, Maliogka et al. 2008). Virus species in this com- plex belong to the family Closteroviridae, primarily in the genus Ampelovirus. Within this virus complex, GLRaV-3 is the predominant species in most vineyards worldwide (Habili et al. 1995, Sforza et al. 2003, Martin et al. 2005, Cabaleiro and Segura 2006, Coetzee et al. 2010) with reported yield losses up to 40% (Credi and Babini 1997, Woodham et al. 1984). This virus not only impacts vine health and grape quality but also has been implicated in graft incompatibility and young vine failure (reviewed by Charles et al. 2006). 1 Department of Entomology, National Taiwan University, Taipei 106, Taiwan. 2 Corresponding author, e-mail: chiwei@ntu.edu.tw. 3 Di.Va.P.R.A., Entomologia e Zoologia applicate allÕAmbiente, Uni- versita ´ degli Studi di Torino, Via L. da Vinci, 44, Grugliasco (TO), 10095, Italy. 4 Department of Environmental Science, Policy and Management, University of California, Berkeley, CA 94720. 0022-0493/11/1480Ð1485$04.00/0  2011 Entomological Society of America