Glassy-winged Sharpshooter Research Articles

BIOLOGY OF ZAGELLA DELICATA (HYMENOPTERA: TRICHOGRAMMATIDAE), AN EGG PARASITOID OF THE SHARPSHOOTER TAPAJOSA RUBROMARGINATA (HEMIPTERA: CLYPEORRHYNCHA: CICADELLIDAE) IN ARGENTINA

Abstract Research on biological control of glassy-winged sharpshooter (GWSS) Homalodisca coagulata (Say) started in the 1990s. This sharpshooter, vector of Pierce’s disease bacteria Xylella fastidiosa Wells, expanded its geographical distribution and it has become a very serious pest problem in several crops, especially grapes, in southern California. In 2000, a survey of sharpshooter egg parasitoids was initiated in Argentina. Fourteen species of egg-parasitoids were collected. We report here on laboratory studies of adult longevity, oviposition preference, sex ratio, and development time of Zagella delicata De Santis. Field result of the incidence on its hosts and seasonal occurrence also are provided. Zagella delicata produced one adult per host egg. The overall results indicated that 72.5% of the sharpshooter eggs exposed to Z. delicata were parasitized. Wasps emergence was 43.8%. In host plant searching preference tests, Z. delicata females parasitized 66.7% of host eggs on sugar cane, 57.0% of eggs ...

OVIPOSITION PREFERENCE OF HOMALODISCA COAGULATA FOR TWO CITRUS LIMON CULTIVARS AND INFLUENCE OF HOST PLANT ON PARASITISM BY GONATOCERUS ASHMEADI AND G. TRIGUTTATUS (HYMENOPTERA: MYMARIDAE)

Oviposition preference of Homalodisca coagulata (Say) and two of its mymarid egg parasitoids, Gonatocerus ashmeadi Girault and G. triguttatus Girault, for two Citrus limon L. cultivars (‘Eureka’ and ‘Lisbon’) was investigated. In laboratory oviposition choice tests, the number of leaves containing H. coagulata egg masses, the number of H. coagulata egg masses, and the total number of H. coagulata eggs were significantly higher at 187.2%, 204.2%, and 181.7%, respectively, on ‘Eureka’ versus ‘Lisbon’. In the field, there was no significant difference in the number of H. coagulata motiles counted in five-minute searches of foliage on ‘Eureka’ and ‘Lisbon’ trees, and numbers of leaves with old (emerged) and new (unemerged) H. coagulata egg masses were equivalent between field-planted cultivars. In the laboratory, parasitism of H. coagulata egg masses by G. ashmeadi and G. triguttatus was 18.6% and 23.2% higher, respectively, for eggs laid on ‘Eureka’ leaves compared to ‘Lisbon’, but these differences were not significant. Leaf surface morphology and thickness of leaf cell layers of both lemon cultivars were compared with scanning electron microscopy (SEM). SEM demonstrated that total leaf thickness and the thickness of the palisade layer was 19.2% and 38.6% higher, respectively, in ‘Eureka’ leaves compared to ‘Lisbon’, and that H. coagulata egg placement was between the lower epidermis and spongy parenchyma layer for both cultivars. Furthermore, ‘Lisbon’ leaves had a smooth underside, whereas ‘Eureka’ leaves had many small ridges. The thickness and rough surface of ‘Eureka’ leaves may be beneficial for H. coagulata oviposition. However, additional research is required to further investigate whether leaf characteristics or xylem chemistry are responsible for H. coagulata oviposition choice. For mass rearing programs with lemons as host plants, it is recommended that the ‘Eureka’ cultivar be used in preference to ‘Lisbon’ because H. coagulata prefers this cultivar for oviposition and parasitoid foraging is not adversely affected.

Molecular distinction between populations of Gonatocerus morrilli, egg parasitoids of the glassy-winged sharpshooter from Texas and California: Do cryptic species exist?

Two molecular methods were utilized to distinguish geographic populations of Gonatocerus morrilli (Howard) from Texas and California and to test the possibility that this species could exist as a species-complex. Inter-Simple Sequence Repeat–Polymerase Chain Reactions (ISSR–PCR) were performed with a 5′-anchored ISSR primer. Twenty-five markers were generated with four populations (40 individuals) of G. morrilli. Twenty-three were polymorphic and the percentage of polymorphic loci was 92%. Most markers could be considered diagnostic since there was no band sharing between the Texas and California populations. Such differences typically are not found unless the populations are reproductively isolated. Exact tests for population differentiation indicated significant differences in marker frequencies among the populations. Comparison of other genetic differentiation estimates, which evaluate the degree of genetic subdivision, demonstrated excellent agreement between GST and θ values, 0.92 and 0.94, respectively, indicating that about 92 to 94% of the variance was distributed among populations. The average genetic divergence (D), as measured by genetic distance, was extremely high (Nei = 0.82 and Reynolds = 2.79). A dendrogram based on Nei's genetic distance separated the Texas and California populations into two clusters, respectively. Amplification of the Internal Transcribed Spacer-1 (ITS-1) region showed no size differences, whereas the ITS-2 DNA fragment varied in size between the two geographic populations. The ITS-2 fragment sizes were about 865 and 1099 base pairs for the California and Texas populations, respectively. The present study using the two molecular methods provides novel data critical to the glassy-winged sharpshooter/Pierce's disease biological control program in California.ISSR–PCR Inter-Simple Sequence Repeat–Polymerase Chain Reaction ITS Internal Transcribed Spacer

Plant Hosts of Xylella fastidiosa In and Near Southern California Vineyards.

Xylella fastidiosa is a xylem-limited bacterium that causes Pierce's disease (PD) of grapevines. A variety of plant species found near a severe outbreak of PD in vineyards in the Temecula Valley of California were tested using enzyme-linked immunosorbent assay, culture on media, and polymerase chain reaction to identify potential inoculum sources in the area. Species that consistently tested positive for X. fastidiosa were the known hosts, grape, almond, and oleander, and two new hosts, Spanish broom (Spartium junceum) and wild mustard (Brassica spp). Sequence analysis of the 16S-23S rRNA spacer region found that strains isolated from grapevine, Spanish broom, wild mustard, and almond clustered with previously sequenced PD strains. Thus, these species could serve as sources of inoculum for infection of grapevines and should be removed or monitored for signs of infection. Sequences from oleander isolates from Temecula formed another cluster with a previously published oleander strain sequence. Oleander strains do not infect grapevines and thus do not appear to cause a direct threat to grapevines. Two additional isolates from almond were determined to be genetically different from PD strains, and the ability of these strains to infect grapevine is not known. Greenhouse transmission studies indicate that the glassy-winged sharpshooter was able to transmit a PD strain of X. fastidiosa to Spanish broom, black mustard, and other hosts.

Impact of pymetrozine on glassy-winged sharpshooter feeding behavior and rate of Xylella fastidiosa transmission

Pymetrozine is a compound that interferes with insect feeding and interrupts transmission of plant pathogens. The glassy-winged sharpshooter, Homalodisca coagulata Say (Hemiptera, Cicadellidae), is a vector of Xylella fastidiosa, the foregut-borne, propagative bacterium that causes Pierce's disease of grapevine. In this study, we recorded the behavioral response of H. coagulata to plants treated by soil drench with pymetrozine using time-lapse photography, quantified the reduction in liquid excreta produced by H. coagulata fed on pymetrozine-treated plants, and evaluated pymetrozine effectiveness in reducing transmission rate in grapevines. H. coagulata feeding on plants treated with 0.015 mg of pymetrozine was disrupted by decreasing the number of contacts made with the grapevine by more than 50% and by increasing movements away from the stem by more than 5-fold. Excreta production by H. coagulata was significantly reduced on plants treated with 0.015 or 0.0075 mg of pymetrozine. Contrary to the expected outcome, the mean number of X. fastidiosa-infected plants actually increased in the pymetrozine treatments relative to the controls.

Analysis of the Spatial Patterns of Pierce's Disease Incidence in the Lower San Joaquin Valley in California

ABSTRACT The incidence of Pierce's disease (PD), caused by Xylella fastidiosa, was monitored in 11 naturally infested commercial vineyards to determine the presence of an X. fastidiosa vector, Homalodisca coagulata (glassy-winged sharpshooter [GWSS]), to examine the spatial patterns of the disease and elucidate possible influences of surrounding environments. Disease incidence ranged from <1 to 65% among vineyards in 2001. Our efforts to trap or capture potential disease vectors have indicated that the GWSS is the most likely vector. Disease incidence doubled in most vineyards during the 2002 production season. Spatial patterns of symptomatic vines in 2001 and 2002, as determined by ordinary runs analysis, showed strong evidence for within- and across-row aggregation of infected vines. In most fields, they were no disease gradients observed relative to GWSS source (e.g., citrus). Within fields, however, disease incidence displayed strong spatial dependence and a high degree of anisotropy, indicating strongly aggregated patterns of disease with distinct directional orientation. The within-row (0 degrees ) and across-row (90 degrees ) orientations generally were the predominant directions of increased disease incidence, consistent with vine-to-vine spread of X. fastidiosa. We concluded that the distribution of PD in vineyards reflected the feeding pattern of vectors carrying X. fastidiosa. Based on these results, effective PD management is likely to be based on practices that reduce significant insect vector populations and remove infected vines as soon as identified and on the use of resistant cultivars.

Spatial and temporal distribution of imidacloprid and thiamethoxam in citrus and impact on Homalodisca coagulata populations

Titers of two systemic neonicotinoid insecticides in citrus trees were measured in conjunction with conventional evaluations of their impact on glassy-winged sharpshooter (Homalodisca coagulata (Say); GWSS) populations. Xylem fluid samples were collected at regular intervals and from multiple locations within field-grown citrus trees to determine imidacloprid and thiamethoxam concentrations using commercial ELISA kits. Uptake profiles varied considerably with peak mean titers of imidacloprid occurring 6-8 weeks after application compared with 2 weeks for thiamethoxam. The persistence of each compound also varied as near-peak levels of imidacloprid were sustained for another 6-10 weeks before gradually declining. In contrast, thiamethoxam titers declined more rapidly after the initial peak, possibly reflecting an application rate only one-quarter of that used for imidacloprid. Within-tree distributions were more similar for the two compounds, with no significant effect due to height of the sample (upper or lower half) or to the quadrant location within the tree, with the exception of one quadrant in the thiamethoxam-treated trees. Substantial reductions in GWSS nymphs and adults were observed in imidacloprid-treated trees during the 2001 trial and were sustained for 4-5 months after treatment. Treatment effects on nymphs were not as well pronounced in the 2002 trial, when overall GWSS infestations were much reduced from the previous year. However, consistently lower adult infestations were still observed in 2002 for both treatments compared with untreated trees. Information on the spatial and temporal profiles in citrus trees was obtained for both compounds to complement field impact data and improve understanding of their pest management potential.

Novel Methods of Monitoring the Feeding Behavior of &lt;I&gt;Homalodisca coagulata&lt;/I&gt; (Say) (Hemiptera; Cicadellidae)

Abstract The glassy-winged sharpshooter, Homalodisca coagulata (Say), is an important agricultural pest because it is an effective vector of Xylella fastidiosa, the pathogen that causes Pierce’s disease in grapevines. Knowledge of the feeding behavior of H. coagulata is important in understanding pathogen transmission, and this knowledge is important in developing innovative pathogen control strategies. Ingestion of fluid by sharpshooters was monitored as movement of fluid from reservoirs connected to short stems of plant tissue. We quantified the amount of fluid processed while the insects were freely moving on the plants stems offered for feeding. Females fed longer than males, and both ingested large amounts of plant fluid and both excreted large amounts of fluid. Excreta droplets were often actively flung from the body by flicking the abdomen. While actively ingesting, the abdomen made exaggerated movements that stopped during excretion. These movements only appeared after mouthparts penetrated the pl...

DISPERSAL ADAPTATIONS OF IMMATURE STAGES OF THREE SPECIES OF LEAFHOPPER (HEMIPTERA: AUCHENORRYNCHA: CICADELLIDAE)

Xylem-feeding leafhoppers have evolved several behavioral and physiological adaptations to utilize xylem fluid of variable composition, including polyphagy and high assimilation efficiency. They also display high vagility coupled with excellent visual acuity. We investigated the spectral frequency responses of the nymphal stages of three leafhopper species: Homalodisca coagulata, H. insolita, and Oncometopia nigricans. Under laboratory conditions, the nymphs of H. coagulata and O. nigricans discriminated spectra and were highly attracted to hues of yellow, with safety yellow being the most attractive. The nymphs of H. insolita were also attracted to yellow hues, but were more attracted to cream yellow. In the laboratory, maximum jumping distances of third instar H. coagulata, H. insolita, and O. nigricans were 68.0, 49.7, and 39.2 cm respectively, when provided a target. The fifth instars of H. coagulata, H. insolita, and O. nigricans had maximum jumping distances of 78.8, 29.2, and 45.5 cm, respectively. Additionally, all nymphal stages of H. coagulata dispersed up to 10 meters after three days under field conditions when released into an outdoor grass-covered arena. The neonates of H. coagulata, H. insolita, and O. nigricans survived on average, 83.5, 70.5, and 83.0 h without plant feeding, respectively.

Species identity of geographically distinct populations of the glassy-winged sharpshooter parasitoid Gonatocerus ashmeadi: morphology, DNA sequences, and reproductive compatibility

Abstract Gonatocerus ashmeadi is a common and seemingly widespread egg parasitoid of Homalodisca coagulata , the glassy-winged sharpshooter (GWSS). Location records for G. ashmeadi indicate its natural range to be the southeastern USA and northeastern Mexico (which coincides with the presumed native range of GWSS), and possibly southern and central California (CA) (the adventive range of GWSS). The purpose of our work was to determine whether G. ashmeadi in the USA and northeastern Mexico is one species or a complex of reproductively incompatible sibling species. We used three approaches to determine the species identity of different G. ashmeadi populations: (1) reassessment of key morphological features using scanning electron microscopy (SEM) to determine if subtle morphological differences exist between G. ashmeadi populations which could indicate species differences; (2) to determine if molecular differences exist between G. ashmeadi populations collected from different regions by comparing mitochondrial and ribosomal DNA sequences; (3) mating compatibility studies to determine if different populations of G. ashmeadi are reproductively isolated, or if mating occurs, whether offspring are viable thereby defining species groups on the basis of successful interbreeding. Results from these three areas (morphology, DNA sequences, and reproductive compatibility) have been evaluated collectively; leading us to the conclusion that G. ashmeadi as it is currently viewed is a valid species and not an aggregate of morphologically indistinguishable cryptic species.

Appearance of Xylella Fastidiosa in Pierce's Disease resistant and Susceptible Grapevines

Pierce's Disease (PD) is a major factor limiting grape production in the southeast United State. This disease is caused by a bacterium, Xylella fastidiosa Wells et al., which is transmitted to the xylem system of the grapevines primarily by glassy-winged sharpshooters (Homalodisca coagulata Say). Once it is in the xylem, the X. fastidiosa will use the xylem sap as a nutrient source to multiply, colonize, and eventually plug the xylem vessels and cause the PD in susceptible cultivars. On the other hand, symptoms of PD in tolerant cultivars do not appear until fruit maturation, and symptoms are rarely observed in PD resistant cultivars. In order to understand the correlation between X. fastidiosa and PD symptom development, a study was initialed to monitor X. fastidiosa in xylem of resistant, tolerant, and susceptible vines on a monthly basis. Presence of X. fastidiosa was detected directly from xylem sap of field-grown vines by medium culture and confirmed by polymerase chain reaction (PCR). Xylella fastidiosa was detectable throughout the growing season in PD susceptible cultivar `Chardonnay', PD tolerant Florida hybrid grape `Blanc du Bois', and muscadine cultivar `Carlos'. The bacteria were also appeared in the dormant vines with high density in cultivars `Chardonnay' and `Blanc du Bios'. Although X. fastidiosa was also found in dormant canes of `Carlos', the density decreased throughout the late fall and winter months, and they were hardly found before June. The results indicated that X. fastidiosa were carried over from previous season in cultivars `Chardonnay' and `Blanc du Bois', while in PD tolerant cultivar `Carlos', they were newly acquired from the sharpshooter feedings during the growing season.

Population Genetic Structure of &lt;I&gt;Homalodisca coagulata&lt;/I&gt; (Homoptera: Cicadellidae), the Vector of the Bacterium &lt;I&gt;Xylella fastidiosa&lt;/I&gt; Causing Pierce’s Disease in Grapevines

In the current study, inter-simple sequence repeat (ISSR) primers (p-13 and p-15) were used to estimate the population genetic structure of the sharpshooter Homalodisca coagulata (Say) (Homopera: Cicadellidae). Eighteen populations from throughout the United States and a population from Tahiti, French Polynesia, were analyzed. Populations were arbitrarily assigned to three regions: southeastern, southwestern, and western. Exact tests for population differentiation indicated highly significant differences in marker frequencies among the 18 populations with both primers. Analyses of molecular variance also indicated significant geographic structuring with both primers. A dendrogram based on Reynolds coancestry distance performed with p-15 clustered the U.S. populations into two main groups. The southeastern populations were grouped into one cluster and the southwestern and western populations into a second cluster. Within the western region, dendrograms produced with p-13 and p-15 showed in both cases that two populations (Edison and Bakersfield) clustered as outliers. The average divergence (D) among all populations was 0.099. Divergence values of 0.254, 0.103, and 0.102 were observed when comparing Bakersfield and the southeastern, southwestern, and western populations, respectively. Within the western region, D values for Bakersfield were 1.8- (p-13) and 2.4-fold (p-15) higher than the D of the western populations. The present results suggest that a subset of insects in California may have their origins in the southwestern region (Texas); furthermore, these results are suggestive of more than one founding event in California and/or biotypes or geographic races.

FUNGAL PATHOGENS OF THE GLASSY-WINGED SHARPSHOOTER HOMALODISCA COAGULATA (HOMOPTERA: CICADELLIDAE)

An epizootic of fungal diseases on glassy-winged sharpshooters was examined in the autumn of 2002 in Mississippi, USA. Trichothecium roseum and Beauveria bassiana were identified from the cadavers of the sharpshooter bearing conidiophores, but these fungi appeared to be either secondary pathogens or saprobes rather than primary pathogens of the sharpshooter. Pseudogibellula formicarum was determined to be the cause of the epizootics. However, additional studies are need to provide a better understanding of host-pathogen interactions, and identify the factors that enhance or limit disease increase in sharpshooter populations under natural conditions. In addition, the sharpshooter was found to be also a suitable host for Metarhizium anisopliae. Overall, P. formicarum and M. anisopliae could provide new avenues for the biological control of the glassy-winged sharpshooter and complement current control strategies.

Evaluation of Methods for Extracting &lt;I&gt;Xylella fastidiosa&lt;/I&gt; DNA from the Glassy-Winged Sharpshooter

Evaluation of Methods for Extracting &lt;I&gt;Xylella fastidiosa&lt;/I&gt; DNA from the Glassy-Winged Sharpshooter

Delivery of a Genetically Marked Alcaligenes sp. to the Glassy-Winged Sharpshooter for Use in a Paratransgenic Control Strategy

An artificial feeding system was designed for the glassy-winged sharpshooter (GWSS), Homalodisca coagulata Say (Hemiptera: Cicadellidae). The system, unlike previous systems, provided enough nutrients to GWSS to survive for 48 h. A system like this is a prerequisite to examining the potential use of paratransgenesis to interrupt transmission of Xylella fastidiosa, the bacterial pathogen causing Pierce's disease of grape, by insect vectors. We developed a system for short-term feeding of GWSS that allows for the introduction of bacteria in liquid medium, and we have demonstrated the ability of Alcaligenes xylosoxidans denitrificans, expressing a red fluorescent protein (dsRed), to colonize the cibarial region of the GWSS foregut for up to 5 weeks post-exposure. Alcaligenes xylosoxidans denitrificans thus occupies the same region in the foregut as the pathogen, Xylella fastidiosa.

Detection of DNA Polymorphisms in &lt;I&gt;Homalodisca coagulata&lt;/I&gt; (Homoptera: Cicadellidae) by Polymerase Chain Reaction-Based DNA Fingerprinting Methods

DNA polymorphisms were detected in Homalodisca coagulata (Say) (Homoptera: Cicadellidae) with the following DNA fingerprinting methods: inter-simple sequence repeat-polymerase chain reaction (ISSR-PCR) and primer pair-ISSR-PCR (pp-ISSR-PCR), randomly amplified microsatellite polymophisms (RAMP), selective amplification of microsatellite polymorphic loci (SAMPL), and primer pair-random amplification of polymorphic DNA-polymerase chain reaction (pp-RAPD-PCR). But first, a small-scale DNA fingerprinting screening procedure was initiated with these methods with a few individual insects to estimate the most sensitive and efficient method(s). In total, 205 polymorphic markers were generated with the four methods. The efficiency ratio estimated the following order for each method: 1) pp-ISSR-PCR and ISSR-PCR, 2) RAMP, 3) pp-RAPD-PCR, and 4) SAMPL. The screening efficiency ratio estimated that pp-ISSR-PCR and ISSR-PCR were the most efficient methods. DNA polymorphisms were detected in a natural population of 10-30 insects. The number of polymorphic loci ranged from five (pp-RAPD-PCR reaction 6) to 32 (ISSR-PCR primer 13), and the percentage of polymorphic loci was 100% for most primers tested. DNA fingerprinting methods tested were able to detect geographic variation in populations of H. coagulata from Bakersfield and Riverside, CA, and Weslaco, TX. Dendrograms based on Nei's genetic distance showed that H. coagulata from Bakersfield and Riverside formed a cluster separate from Weslaco in three DNA fingerprinting reactions tested incorporating simple sequence repeats. DNA fingerprinting methods tested were also able to distinguish between three Homalodisca sharpshooters: H. coagulata, Homalodisca insolita (Walker), and Homalodisca liturata (Ball). The present results confirmed the utility of the DNA fingerprinting screening procedure and demonstrated, for the first time, genetic variation in natural populations of glassy-winged sharpshooters by PCR-based DNA fingerprinting methods.

Overwintering Biology, Food Supplementation and Parasitism of Eggs of Homalodisca Coagulata (Say) (Homoptera: Cicadellidae) by Gonatocerus Ashmeadi Girault and Gonatocerus Morrilli (Howard) (Hymenoptera: Mymaridae)

The efficiency of parasitism of Gonatocerus ashmeadi Girault and G. morrilli (Howard) (Hymenoptera: Myramidae) on glassy-winged sharpshooter, Homalodisca coagulata (Say) (Homoptera: Cicadellidae), eggs of varying age was documented. Excised leaves with H. coagulata eggs of age 1 to 9 d were presented to mated female parasitoids in Petri dishes as well as on intact foliage. Parasitism rates for both species were high with 3 females in Petri dishes parasitizing virtually all eggs in 3 egg masses, and 8 mated females finding and parasitizing almost all eggs from 5 egg masses in small shrubs of Ilex opaca cv cornuta. For both species, parasitism efficiency exceeded 95% within 24 h. Parasitism rates declined for older eggs (8 and 9 d) on excised leaves. Because this did not occur on live plant material, hardening of excised foliage likely contributed to lower rates of parasitism. No cases of superparasitism were observed: Overwintering of the parasitoids was examined by monitoring the fate of eggs of H. coagulata deposited in November. We documented the first case of H. coagulata overwintering as eggs under North Florida conditions. In addition, both G. ashmeadi and G. morrilli were able to overwinter as undeveloped larvae within parasitized eggs under similar conditions. Overwintering parasitoids took approximately 85 d for emergence, which slightly exceeded the minimum predicted for emergence by existing degree day models. Feeding experiments conducted with G. ashmeadi and G. morrilli as food sources are limited during winter/spring; however, our results confirmed that honeydew from Dialeurodes citri (Ashmead) (available in North Florida in late winter/early spring) significantly increased the longevity of both parasitoid species when compared to honey and water.

Comparative Nutrition and Developmental Biology of Xylem-Feeding Leafhoppers Reared on Four Genotypes of &lt;I&gt;Glycine max&lt;/I&gt;

A simplified protocol for rearing the glassy-winged sharpshooter, Homalodisca coagulata (Say) (Homoptera: Cicadellidae), was tested on four genotypes of soybean, Glycine max (L.) Merrill. Growth and development of leafhoppers were examined on three glabrous isolines (D88-5320, D88-5328, and D90-9216) and one pubescent genotype (Hagood). All three glabrous isolines were adequate hosts producing an average of >100 adults from eight original mating pairs of leafhoppers. Pubescent Hagood produced significantly fewer adults with longer developmental times. Isoline D88-5328 produced 30% more adults than the other glabrous isolines. Genotype also had significant effects on total developmental times, developmental rates within instars, growth rates, and adult masses at eclosion with insect performance being enhanced on isoline D88-5328. All genotypes of G. max had similar xylem chemistry at the initiation of the rearing experiment (6-week-old plants), but as G. max matured (14–18 wk), isoline D88-5328 provided significantly more organic nitrogen. Chemical analyses of xylem fluid and developmental data support the hypothesis that young H. coagulata required balanced profiles of organic nitrogen for development but benefited from increased organic nitrogen as they approached maturation. Poor performance on pubescent Hagood was not related to xylem chemistry and was assumed to result from the inhibitory effect of trichomes. Xylem fluid analysis suggests that some plants may have eventually experienced nitrogen deprivation from high leafhopper loads; this, in turn, resulted in slow development and small body size at maturation for some insects. Although this protocol provides a simplified technique for rearing H. coagulata, it is likely that manipulation of xylem chemistry via fertilization would further maximize growth and developmental rates.

The potential adventive geographic range of glassy-winged sharpshooter, Homalodisca coagulata and the grape pathogen Xylella fastidiosa: implications for California and other grape growing regions of the world

The invasion risk posed by the xylem feeding hemipteran, Homalodisca coagulata (native to the southeast USA and northeast Mexico, and a recent invader of California (USA) and Tahiti) and a xylem-dwelling phytopathogenic bacterium, Xylella fastidiosa (native to the Americas and causative agent of Pierce's disease of grape vines), was examined using the computer climate modeling program CLIMEX. Model predictions indicated that suitable climatic conditions for H. coagulata and Pierce's disease causing strains of X. fastidiosa exist in almost all grape production areas of the world, and H. coagulata may be able to colonize areas unsuitable for X. fastidiosa. Additionally, the model indicated that regions north of California will be unable to sustain populations of both pests because of cold stress, and that irrigation of agricultural and urban areas in California's deserts has removed dry stress limitations, which when combined with a depauperate natural enemy fauna most likely facilitated successful invasion by H. coagulata. CLIMEX predicted that cold stress accumulation would exclude Pierce's disease causing strains of X. fastidiosa from France and northern and central grape producing areas of Spain and Italy. This result is incongruous with Pierce's disease reports from Kosovo in the Balkans and may suggest that cold-tolerant strains of X. fastidiosa that cause Pierce's disease exist which could exhibit invasion potential and establish in areas of Europe contrary to results reported here.

Comparative Dispersal ofHomalodisca coagulataandHomalodisca liturata(Homoptera: Cicadellidae)

Abstract California’s viticulture and ornamental industries have suffered significant losses since the introduction of Homalodisca coagulata (Say), an important vector of the Pierce’s disease bacterium. A better understanding of the factors that influence the dispersal of H. coagulata, as well as other native sharpshooters could enhance our ability to institute areawide management programs. Studies were conducted to establish the validity of an immunoglobulin G (IgG) protein marker for sharpshooter dispersal studies, to compare the dispersal of H. coagulata with that of a native sharpshooter Homalodisca liturata Ball, and to develop a better understanding of the factors that influence their dispersal. Field trials showed that the marker remained detectable for at least 19 d and did not affect sharpshooter survival. Four concentrations (0.04, 0.2, 1, and 5 mg/ml) and two different IgG markers (chicken and rabbit) were effective for marking sharpshooters. In mass-mark-recapture studies, ≈95% of the marked i...