© 2005 The Netherlands Entomological Society Entomologia Experimentalis et Applicata 117: 95–103, 2005 95 Blackwell Publishing, Ltd. Influence of Xylella fastidiosa infection of citrus on host selection by leafhopper vectors R.C. Marucci 1 , J.R.S. Lopes 2 , J.D. Vendramim 2 & J.E. Corrente 3 1 Faculdade de Ciências Agrárias – FACIAGRA/UNIPAM, CP. 485, Patos de Minas, MG 38702-054, Brazil; 2 Departamento de Entomologia, Fitopatologia e Zoologia Agrícola, ESALQ/Universidade de São Paulo, CP. 9, Piracicaba, SP 13418-900, Brazil; 3 Departamento de Ciências Exatas, ESALQ/Universidade de São Paulo, CP. 9, Piracicaba, SP 13418-900, Brazil Accepted: 4 May 2005 Key words: citrus variegated chlorosis, disease symptoms, leafhopper behavior, sharpshooter epidemiology, Dilobopterus costalimai, Oncometopia facialis, Homoptera, Cicadellidae Abstract Infection of plants by pathogens can influence their attractiveness and suitability to insect vectors and other herbivores. Here we examined the effects of Citrus sinensis (L.) Osbeck (Rutaceae) infection by the bacterium Xylella fastidiosa, which causes citrus variegated chlorosis (CVC), on the feeding preferences of two sharpshooter vectors, Dilobopterus costalimai Young and Oncometopia facialis (Signoret) (Homoptera: Cicadellidae). Experiments were performed inside observation chambers, in which a healthy plant and an infected one (with or without CVC symptoms) were supplied to a group of 40 sharpshooters. The number of insects that selected each treatment was recorded at several time intervals in 48 h. In another experiment, the ingestion rate on healthy and infected (symptomatic or not) plants was evaluated by measuring the liquid excretion of sharpshooters that were confined on branches of each plant for 72 h. Both sharpshooter species preferred healthy plants to those with CVC symptoms. However, O. facialis did not discriminate between healthy citrus and symptomless infected plants. Feeding by D. costalimai was markedly reduced when confined on CVC-symptomatic plants, but not on asymptomatic infected ones. The ingestion rate by O. facialis was not affected by the presence of CVC symptoms. The results suggest that citrus trees with early (asymptomatic) infections by X. fastidiosa may be more effective as inoculum sources for CVC spread by insect vectors than those with advanced symptoms. Introduction Xylella fastidiosa is a xylem-limited bacterium that infects and colonizes a large number of plant species, which frequently show no symptoms. It is classified as a single species, although recent genetic studies support the separation of groups of strains in multiple taxa or subspecies (Schaad et al., 2004). The feeding of insect vectors from xylem sap of host plants is a requirement for its transmission (Purcell & Hopkins, 1996). Thus, X. fastidiosa can be transmitted by sharpshooter leafhoppers (Homoptera: Cicadellidae) and spittlebugs (Homoptera: Cercopidae), which are xylem-feeders (Purcell, 1989). In the United States, this pathogen is responsible for diseases in important crops, e.g., grapevines, peach, alfafa, almond, plum, and forest species, as well as in plants with no economic relevance (Hopkins, 1989). However, X. fastidiosa strains vary in host specificity (Sherald, 1993), in that not all plants are susceptible to the same strain. In Brazil, X. fastidiosa is the causal agent of citrus variegated chlorosis (CVC; Chang et al., 1993; Lee et al., 1993), coffee leaf scorch (Paradela Filho et al., 1995), and plum leaf scald (French & Kitajima, 1978), besides infecting a large number of other plants that show no symptoms (Leite et al., 1997; Lopes et al., 2003). The efficiency of X. fastidiosa transmission by sharp- shooters in citrus [Citrus sinensis (L.) Osbeck (Rutaceae)] is low and variable among vector species (0.3–30%) (Krügner et al., 2000; Yamamoto et al., 2002; Marucci et al., 2003). This could be due to many factors, such as the low concen- tration of the pathogen in citrus (Almeida et al., 2001) and its irregular distribution in the xylem bundles (Mizubuti et al., 1994), host plant preference (Raju et al., 1982), and behavioral patterns of the sharpshooters related to feeding and movement in orchards (Purcell, 1985). The low rates of sap ingestion and survival by sharpshooters on healthy *Correspondence: João Roberto Spotti Lopes, Departamento de Entomologia, Fitopatologia e Zoologia Agrícola – ESALQ/USP, Av. Pádua Dias, 11, Piracicaba, SP 13418-900 Brazil. Tel. +55 (19) 3429-4199; E-mail:jlopes@esalq.usp.br