Abundance and Consumption Rate of Glassy-Winged Sharpshooter (Hemiptera: Cicadellidae) on Peaches and Plums Peter C. Andersen, 2 Russell F. Mizell, Ill, Brent V. Brodbeck, Thomas G. Beckman,3 and Gerard Krewer4 University of Florida, North Florida Research and Education Center, Quincy Florida 32351 USA J. Entomol. Sd. 43(4): 394-407 (October 2008) Abstract Homalodisca vitriperinis (Germar), the glassy-winged sharpshooter, is a primary vector of phony peach and plum leaf scald diseases caused by XyIe/Ia fastidiosa Wells et al. A survey of H. vifripennis on peach [Prunus persica (L.) Batsch] varieties established that leaf- hopper abundances varied from 0-13 per tree. Prunus persica cvs. Flordaking and June Gold and Prunus salicina Lindl. (cvs. Methley and Santa Rosa) were then budded on each of 3 P. persica rootstocks (cvs. Aldrighi, Lovell and Nemaguard). Leafhopper abundance was moni- tored on each of the two scions budded on each rootstock and on non budded rootstocks over a 2-yr period. The genotypes were container-grown in Year 1 and were planted in the field in Year 2. For both years leafhopper abundance was greatest during early June and on Methley and Santa Rosa cultivars compared with the peach genotypes. The feeding rates of leafhoppers were substantially higher on plum scions than on peach scions, and nocturnal feeding rates were often higher than daytime feeding rates. Mean leafhopper feeding rates were correlated with leafhopper abundance on Prunus genotypes from 3-8 June in a quadratic manner (F = 53.8; df= 2,12: R 2 = 0.90; P< 0.0001); the mean nighttime feeding rate was best correlated linearly to mean cumulative leafhopper abundance (F= 446.9; df= 1,13; R = 0.972; P< 0.0001). Key Words abundance, consumption rate, glassy-winged sharpshooter, Homalodisca vitrip- cnn/a, leafhopper The glassy-winged sharpshooter, Homalodisca vitriperinis (Germar) [=Homalo- disca coagulata (Say)] (Takiya et al. 2006), is endemic to the southeastern United States and northeastern Mexico (Redak et al. 2004, Turner and Pollard 1959). Homa- lodisca v/fr/penn/s is a primary vector of xylem-limited diseases caused by XyIeIIa fastidiosa Wells et al. (Hopkins and Purcell 2002, Wells et al. 1987). In the south- eastern United States, H. vitripennis is one of the most important problems in the culture of plums (Prunus salicina Lindl.) (e.g., vectoring plum leaf scald) and peaches [Prunus persica (L.) Batsch] (e.g., vectoring phony peach disease) and precludes a grape industry based on Vitis vinifera L. Homalodisca vitripennis is an exotic pest in California (Sorensen and Gill 1996) where Pierces disease now threatens a multi- Received 03 December 2007; accepted for publication 30 May 2008. 2Address inquires (email: pcand @ ufl.edu). USDA-ARS Fruit and Tree Nut Research Laboratory, Byron, GA 31008. 4 University of Georgia, Tifton, GA 31793. 394 ANDERSEN et al.: Abundance and Consumption Rate of H. vitripennis 395 billion dollar grape industry along with other commodities such as peach, plum and almond (Hopkins and Purcell 2002). Homalodisca vitripennis is highly polyphagous and may feed on hundreds of plant species belonging to many botanical families (Adlerz 1980, Redak et al. 2004, Turner and Pollard 1959), although the seasonal pattern of host plant usage is repeatable from year to year (Brodbeck et al. 1990, Mizell and French 1987). Polyphagy may be critical for H. vitripennis survival because xylem fluid contains the lowest concentra- tion of nutrients of any plant tissue (Andersen and Brodbeck 1 989a,b, Andersen et al. 1995, Mattson 1980, Raven 1983), and nutrient levels in xylem fluid change with host plant phonology (Andersen et al. 2005, Brodbeck et al. 1990). Insects that subsist on xylem fluid consume 100-1000 times their body mass each day (Mittler 1967, Horse- field 1977, Andersen et al. 1989, 1992, Brodbeck et al. 1993, Crews et al. 1998, Ponder et al. 2002). All insects that feed on xylem fluid have well developed cibarial pumps that enable extraction against the negative pressure that exists in xylem vessels (Scholander et al. 1965, Raven 1983). Other characteristics of H. vitripennis that facilitate subsistence on xylem fluid include: (1) a seasonal and diurnal synchro- nization of feeding in response to optimum host nutritional status (Bi et al. 2005, Brodbeck et al. 1990); (2) a high assimilation efficiency of primary organic compounds (amino acids, organic acids and sugars) (Andersen et al. 1989, 1992, Brodbeck et al. 1993); and (3) excretion of ammonia as the primary nitrogenous waste product (Andersen et al. 1989, 1992, Brodbeck et al. 1993). The concentration of secondary compounds is exceedingly low in xylem fluid (Raven 1983). Xylem fluid chemistry of Prunus genotypes and the abundance of H. vitripennis were rootstock dependent and were correlated with concentrations of amino acids in xylem fluid (Brodbeck et al. 1990, Gould et al. 1991). It has been proposed that the amides serve as phagostimulants for adult H. vitripennis (Andersen et al. 1992, 2005, Brodbeck et al. 1993). The objectives of this study were to determine the preference (abundance) and consumption rate of H. vitripennis on 2 peach and 2 plum scions budded on 3 peach rootstocks. Seasonal abundance was determined over a 2-yr period, and consumption rate was measured diurnally during the second year. In addition, xylem fluid osmolality and xylem tension were recorded during the day and night. Leafhopper abundances also were monitored on a diversity of P. persica germ- plasm to assess the range of abundances typically encountered in the southeastern United States. Materials and Methods Prunus salicina L. cvs, Methley and Santa Rosa and P. persica cvs. Floridaking and June Gold" were budded onto Aldrighi (from Brazil, Gould et al. 1991), Lovell and Nemaguard rootstocks at the North Florida Research and Education Center at Monticello (NFREC-Monticello). Each tree was double budded (contained 2 scions) yielding the following combinations of scions: Flordaking/June Gold, Flordaking/ Methley, Flordaking/Santa Rosa, June Gold/Methley, June Gold/Santa Rosa, and Methley/Santa Rosa, each on 3 rootstocks. Control plants also were maintained without budding (Aldrighi on Aldrighi, Lovell on Lovell, Nemaguard on Nemaguard). Each combination was replicated 5 times. Because each scion was not influenced by the other adjacent scion, data were pooled for Flordaking, June Gold, Methley and Santa Rosa for each of three rootstocks. In Year 1, plants were grown in 10-L containers. Media consisted of 2 parts pine bark, 1 part Canadian sphagnum peat, and 1 part sand. The medium was amended 396 J. Entomol. Sd. Vol. 43, No. 4 (2008) I with 1.48 kg dolomite, 2.97 kg superphosphate, 889 g Micromax (12S-0.1B-0.5Cu- l2Fe-2.5Mn-0.O5Mo-lZn) and 5.93 kg Osmocote 18N-2.64P-9.96K (18-6-12) per m3. After the first growing season, trees were planted in the field at a spacing of 4.6 m within rows and 6.1 m between rows. Soil type was a Dothan loamy sand. Drip irrigation was provided for container-grown and field-planted trees. Leafhopper abundance was monitored on the Prunus genotypes from 18 May to 12 August 1987 and from 25 May to 3 August 1988 at the NFREC-Monticello. Insects were counted every 2-10 don container-grown (1987) and field-grown (1988) trees by holding a clipboard on the far side of each scion allowing them to be enumerated. Insect abundance was monitored on the 4 scions on each rootstock (and from control scions). Leafhopper abundance data were subjected to a repeated measures analy- ses (SAS Institute 2003). Multivariate analyses were used to examine between-plant variation and to assess the effects of scion, rootstocks and interactions on leafhopper counts; univariate analyses were performed to examine within-plant variability in leaf- hopper counts over time to assess the significance of date and date x scion and date x rootstock interactions. Additionally, leafhoppers were counted on 30 peach geno- types on 16 and 26 June 1992 at the University of Georgia Attapulgus Research Center to assess abundance on a wide range of genotypes for comparative purposes. Trees were in the second leaf growth stage with a plant spacing of 3.9 m within rows and 6.1 m between rows. Means (±SE) are reported. For feeding experiments, leafhoppers were obtained from a block of crape myrtle, Lagerstroemia id/ca L., located at a local nursery. Leafhopper consumption rate was monitored from 2-8 June 1988 using a feeding assembly (Andersen et al. 1992). Adult H. vitripennis were caged in collection devices that allowed easy quantification and removal of the liquid excreta (the only excretory or digestive waste product). In brief, feeding assemblies were constructed by drilling a hole in the bottom portion of a 50-ml polypropylene centrifuge tube (Nalgene 3150-0050) and gluing a snap cap from a 15-ml tube (Falcon 2057) over the opening. Excreta was collected and measured by removal of a smaller tube inserted in the snap cap. The 50-ml tube was slit to allow easy enclosure of shoots. Leaves were removed from the enclosed shoot. A sponge stopper (2.5 cm diam) was slit on one side, and aluminum foil was wrapped around the assembly to exclude rain and to prevent overheating. Two female leafhoppers were placed in each feeding assembly. Feeding rate was presumed to be equal to excretion rate because evaporative losses under these conditions should be negli- gible. Feeding rate was monitored at various times of the day and overnight. Times of collection were 0800, 1200, 1400, 1600, 2000 h, and midpoints of feeding were 0200 (night), 1000, 1300, 1500 and 1800 h. Feeding rate was correlated with mean abundance for each of 4 scions on each rootstock plus a nonbudded control for each rootstock (n = 15).