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Female black widow spiders, Latrodectus hesperus Chamberlin and Ivie (Araneae: Theridiidae), are solitary predators of arthropods with no tolerance for intruders on the webs. In California, L. hesperus are found in urban and agricultural settings and can be a phytosanitary pest in fresh produce. Spatial separation of L. hesperus webs could be determined by seasonal population densities, with territorial competition expected under high densities in the environment. However, little is known about female-female communication behaviors in this species. In 1-hr laboratory observations, displays of female-female rivalry included production of vibrational signals in a majority (20 of 30) of trials. The number of signals produced by both females was highest during the initial 10 min of trials, with signaling rate (time interval between signals) peaking during the 40–50 min observation period. The overall ratio of signals produced by the resident female and the introduced female was about 5:1, with the number of signals produced by the resident female higher than the number of signals produced by the introduced female. Analysis of rivalry signals showed a peak in magnitude (about 0.4 m/s) ranging from 6 to 23 Hz and smaller peaks at about 29, 38, and 47 Hz. Collectively, these results demonstrate that female L. hesperus exhibit territorial rivalry and that female-female rivalry is mediated by emission of vibrational signals through the web. Understanding the mechanisms of intraspecific competition in L. hesperus is required for elucidating interspecific interactions in the environment and may lead to development of novel methods to prevent spiders from colonizing crops.

Insecticides are a primary means for suppressing populations of insects that transmit plant pathogens. Application of insecticides for limiting the spread of insect-transmitted plant pathogens is often most effective when applied on an area-wide scale. The glassy-winged sharpshooter is a vector of the bacterial pathogen Xylella fastidiosa, which causes numerous plant diseases including Pierce’s disease of grapevine. The glassy-winged sharpshooter has been the subject of an area-wide suppression program in California for nearly two decades. Overreliance on a limited number of active ingredients including the neonicotinoid imidacloprid has resulted in increased levels of resistance to commonly applied products. In California, glassy-winged sharpshooters move between citrus, an important overwintering host, and vineyards. Accordingly, imidacloprid is routinely applied via the irrigation system in vineyards and citrus orchards. For soil applied applications, it may take days to weeks for concentrations in plants to increase to lethal doses. Further, as the dose of imidacloprid required to kill sharpshooters increases due to resistance, so too does the period that sharpshooters are exposed to sub-lethal doses. Response of glassy-winged sharpshooter to cowpea plants treated with sub-lethal doses of imidacloprid was evaluated by conducting no-choice and choice tests. In no-choice feeding assays, glassy-winged sharpshooters caged on plants treated with sub-lethal doses of imidacloprid ceased feeding and produced little excreta. Further, sub-lethal exposure to a range of doses over a 4-d period did not affect viability over a 9-wk post-exposure holding period on untreated plants. In choice-tests, glassy-winged sharpshooters avoided treated plants and were observed predominately on untreated plants. Results suggest that application of imidacloprid to vineyards and citrus orchards may push glassy-winged sharpshooters out of treated habitats rather than kill them.

‘Nemaguard’ is a commonly used rootstock for almond and stone fruits due to resistance to nematodes and enhanced scion vigor. Nemaguard also happens to be resistant to strains of Xylella fastidiosa that cause almond leaf scorch disease. Previous research showed that prior to June-budding, this rootstock can prevent infection of almond nursery stock by X. fastidiosa. Further, the rootstock also promotes recovery from infection in susceptible almond scions. Objectives of this study were to 1) compare movement and bacterial populations of X. fastidiosa in almond and Nemaguard, 2) determine whether the metabolic profile of infected versus noninfected plants of each species correspond with differences in pathogen distribution, and 3) evaluate the impact of feeding on Nemaguard on transmission efficiency and pathogen populations in insects. Results showed limited or no movement of X. fastidiosa beyond the point of mechanical inoculation in Nemaguard, whereas X. fastidiosa was detected in susceptible almond and isolated from plant samples distal to the point of inoculation. Large differences in the concentration of phenolic compounds between Nemaguard and almond were also found, although this was not impacted by infection status. After acquiring X. fastidiosa from infected plants, vector access periods of up to 14 days on Nemaguard neither reduced pathogen populations in vectors nor reduced transmission efficiency of X. fastidiosa to susceptible plants when compared with similar vector-access periods on susceptible grapevines. Results suggest Nemaguard, in spite of having high phenolic concentrations in its xylem, does not directly impact X. fastidiosa survival and that future research should focus on identification of potential physical traits that prevent bacterial attachment, multiplication, or movement within the plant.

Leafhoppers in the tribe Erythroneurini are a concern for grape growers in California due to direct feeding damage by piercing the leaves. Management of leafhopper populations in vineyards may be accomplished by insecticide applications, the release of natural enemies, conservation biological control, exploitation of controlled deficit irrigation, or a combination of the above. Based on research on other leafhopper species, a behavioral mating disruption is a viable option, but nothing is known about the mating communication and circadian signaling of these species in vineyards. The objectives of this study were to identify and describe vibrational signals associated with mate selection behavior of Erasmoneura variabilis and Erythroneura ziczac, and evaluate the occurrence of vibrational signals within sympatric populations of E. variabilis, E. ziczac, and Homalodisca vitripennis on grapevines. Analysis of vibrational communication signals revealed that 1) one female signal and two distinct male signals are used in E. variabilis pair formation, 2) the pair formation process in E. variabilis is divided into three communication phases, 3) E. variabilis pre-copulatory communication is longer in the presence than in the absence of male-male rivalry, 4) two distinct signals are used in E. ziczac pair formation, and 5) E. variabilis, E. ziczac, and H. vitripennis sing at night and during the day. Results include detailed descriptions of leafhopper communication signals that are relevant for future development of vibrational disruption as a novel method to suppress populations under field conditions.

Finding a partner to mate with may be only part of ensuring successful siring of offspring. Females often exhibit cryptic female choice (CFC) during or after copulation, which can influence whose sperm from her multiple partners is chosen for egg fertilization. Known behavioral mechanisms for CFC include assessment of males by their nuptial gifts, duration of copulation, and seminal fluid contents. In this study, the glassy-winged sharpshooter, Homalodisca vitripennis (Germar) (Hemiptera: Cicadellidae), behaviors during the course of copulation were investigated. Glassy-winged sharpshooter (GWSS) use vibrational communication before copulation occurs. However, little is known about behaviors that occur during and after copulation. Results from this study determined that vibrational signaling also occurs during copulation. Vibrational signals similar to those emitted during precopulatory communication were identified during copulation alongside a new, ‘hum-like’ signal that typically occurred within 10 s after the pair joined in copulation. In addition, results determined the duration of copulation was on average of 15 h, though with a 10-h range (8.5–18.5 h) among observed male–female pairs. Finally, both males and females mated more than once. Collectively, results identified key reproductive parameters required for CFC to occur in GWSS. The study expands on the known animals that use CFC and emphasizes the role that copulatory vibrational communication may play setting the foundations for future more in-depth studies. Understanding of insect behaviors necessary for successful production of offspring is important from an ecological perspective and for development of pest control methods.

Xylella fastidiosa is a xylem-limited bacterial plant pathogen that causes disease on numerous hosts. Additionally, X. fastidiosa asymptomatically colonizes a wide range of plant species. X. fastidiosa subsp. multiplex has been detected in olive (Olea europaea) trees grown in California, U.S.A., as well as in Europe. Strains of X. fastidiosa subsp. multiplex isolated from California olive trees are not known to cause disease on olive, although some can induce leaf-scorch symptoms on almond (Prunus dulcis). No genome assemblies currently exist for olive-associated X. fastidiosa subsp. multiplex strains; therefore, a hybrid assembly method was used to generate complete genome sequences for three X. fastidiosa subsp. multiplex strains (Fillmore, LM10, and RH1) isolated from olive trees grown in Ventura and Los Angeles counties of California.

Xylella fastidiosa is a vector-transmitted bacterial plant pathogen that affects a wide array of perennial crops, including grapevines (Pierce’s disease). In the southern San Joaquin Valley of California, epidemics of Pierce’s disease of grapevine were associated with the glassy-winged sharpshooter, Homalodisca vitripennis. During the growing season, rates of X. fastidiosa spread in vineyards are affected by changes in pathogen distribution within chronically infected grapevines and by vector population dynamics. Grapevines chronically infected with X. fastidiosa rarely tested positive for the pathogen prior to July, suggesting vector acquisition of X. fastidiosa from grapevines increases as the season progresses. This hypothesis was supported by an increase in number of X. fastidiosa-positive glassy-winged sharpshooters collected from vineyards during July through September. Analysis of insecticide records indicated that vineyards in the study area were typically treated with a systemic neonicotinoid in spring of each year. As a result, abundance of glassy-winged sharpshooters was typically low in late spring and early summer, with abundance of glassy-winged sharpshooter adults increasing in late June and early July of each year. Collectively, the results suggest that late summer is a crucial time for X. fastidiosa secondary spread in vineyards in the southern San Joaquin Valley, because glassy-winged sharpshooter abundance, number of glassy-winged sharpshooters testing positive for X. fastidiosa, and grapevines with detectable pathogen populations were all greatest during this period.

‘Candidatus Liberibacter asiaticus’, an unculturable α-proteobacterium, is associated with citrus huanglongbing (HLB), a devastating disease threatening citrus production in Brazil and worldwide. In this study, a draft whole-genome sequence of ‘Ca. L. asiaticus’ strain 9PA from a sweet orange (cultivar Pera) tree collected in São Paulo State, Brazil, is reported. The 9PA genome is 1,231,881 bp, including two prophages, with G+C content of 36.7%. This is the first report of a whole-genome sequence of ‘Ca. L. asiaticus’ from Brazil or South America. The 9PA genome sequence will enrich ‘Ca. L. asiaticus’ genome resources and facilitate HLB research and control in Brazil and the world.

Vertical transmission of Homalodisca vitripennis reovirus (HoVRV) from glassy-winged sharpshooter (GWSS, Homalodisca vitripennis (Germar)) females to progeny occurred in laboratory assays at frequencies too low (2.6%–15.4%) to account for HoVRV incidence (90–100%) in field populations resident in citrus. Because citrus is immune to HoVRV and no plant host is known, horizontal transmission of HoVRV from insect-to-insect was evaluated. Exposure of colony-reared, virus-free test nymphs to HoVRV-infected source adults held in the same cage for 10 days on virus-immune cowpea resulted in HoVRV transmission (13.3%–30.7%) to test nymphs. HoVRV was not transmitted when exposure was indirect and required passive movement of virions through the xylem of immune citrus seedlings. Collectively, these results demonstrate direct insect-to-insect horizontal transmission of HoVRV, providing a plausible explanation for high incidence of HoVRV in GWSS field populations in the absence of efficient vertical transmission or a plant host.

The agricultural pest, Homalodisca vitripennis, relies on vibrational communication through plants for species identification, location, and courtship. Their vibrational signal exhibits a dominant frequency between 80 and 120 Hz, with higher frequency, lower intensity harmonics occurring approximately every 100 Hz. However, previous research revealed that not all harmonics are recorded in every signal. Therefore, how the female H. vitripennis vibrational signal changes as it travels through the plant was investigated. Results confirmed that transmission was a bending wave, with decreased signal intensity for increasing distance from the source; moreover, at distances of 50 cm, higher frequencies traveled faster than lower frequencies, suggesting that dispersion of H. vitripennis signal components may enable signaling partners to encode distance. Finally, H. vitripennis generates no detectable airborne signal (pressure wave), yet their low vibrational frequency components are detectable in neighboring plants as a result of leaf-to-air-to-leaf propagation. For instance, with isolated key female signal frequencies, 100 Hz was detected at a 10 cm gap between leaves, whereas 600 Hz was detectable only with a 0.1 cm gap. Together, these results highlight the complexity of vibration propagation in plants and suggest the possibility of the animals using the harmonic content to determine distance to the signaling H. vitripennis source. Electronic supplementary material The online version of this article (10.1007/s00359-019-01366-w) contains supplementary material, which is available to authorized users.

During 2016 and 2017, glassy-winged sharpshooters (GWSS; Homalodisca vitripennis) collected from vineyards with a known history of Pierce’s disease or nearby citrus orchards in Kern County, California were assessed for presence of Xylella fastidiosa by quantitative PCR using total DNA samples extracted from GWSS heads. Conventional PCR products for three X. fastidiosa housekeeping genes (petC, leuA, and holC) were cloned from a subset of X. fastidiosa-positive GWSS DNA samples. Cloned sequences were assigned to X. fastidiosa subspecies based on Single Nucleotide Polymorphism (SNP) signature barcodes (7–12 polymorphic sites per amplicon that differentiate reference genomes of subspecies fastidiosa and multiplex). A total of 2005 clones were sequenced: 1499 (74.8%) were genotyped as subspecies fastidiosa and 491 (24.5%) as subspecies multiplex. Among cloned subspecies fastidiosa sequences, 95.4% had SNP barcodes identical to the corresponding gene present in subspecies fastidiosa strains cultured from Pierce’s disease-affected vines in the same region sampled in 2016 and 2017. Presence of SNP barcodes representing both subspecies in one or more cloned genes was commonly observed within individual GWSS. This observation indicates that populations of X. fastidiosa in some insects consists of two subspecies or of two genotypes of one subspecies in which a proportion of the population was derived from a lineage with a history of horizontal gene transfer and homologous recombination. These conclusions suggest that: 1) individual GWSS may visit multiple host species (inoculum sources); 2) sequential pathogen acquisition events can lead to co-colonization of GWSS; 3) competitive exclusion of X. fastidiosa in the foregut is weak or not operating; and 4) the vector foregut is a potential arena for exchange of genetic material among sympatric X. fastidiosa subspecies.

BACKGROUND Glassy-winged sharpshooter (GWSS), Homalodisca vitripennis (Germar) (Hemiptera: Cicadellidae) is an important vector of the bacterium Xylella fastidiosa, the causal agent of Pierce's disease of grapevine. Area-wide insecticide applications have suppressed GWSS populations for ∼ 25 years, but reduced levels of insecticide susceptibility have been reported. Therefore, alternative methods of control are needed. Objectives of this study were to evaluate the efficacy of playback of vibrational mating communication signals for disrupting mating of GWSS in a natural vineyard setting and to evaluate spectral properties of signal transmission through vineyard trellis. RESULTS Playback reduced mating of GWSS on grapevines. A total of 28 (of 134) male-female pairs mated in the control treatment (silence) and only one (of 134) pair mated when treated with the vibrational signal playback. Playback of vibrational signals through vineyard trellis was affected by distance from the signal source, with frequency composition being the highest at the source and lowest on vines positioned away from the source. Frequency composition in canes housing test insects decreased exponentially as distance from the source increased, whereas the relative amplitude of analyzed frequencies decreased linearly. CONCLUSION Although further studies are needed prior to method implementation, data from this study continue to support integration of vibrational mating disruption with current methods to suppress GWSS populations. Published 2018. This article is a U.S. Government work and is in the public domain in the USA.

BACKGROUND The glassy-winged sharpshooter (GWSS), Homalodisca vitripennis, is an important pest of grapevines due to its ability to transmit Xylella fastidiosa, the causal agent of Pierce's disease. GWSS mating communication is based on vibrational signals; therefore, vibrational mating disruption could be an alternative to insecticides for suppression of GWSS population. Our objectives were to identify spectral features of female signal that elicit male signaling, design disruptive signals able to alter male perception and acceptance of a female, and determine the signal intensity required for future field applications. RESULTS Results showed that male responses to playback of modified female signals were significantly reduced by 60-75%when part of the female signal spectral components above or below 400 Hz were deleted. Playback bioassays showed that transmission of an 80 Hz pure frequency tone to plants completely suppressed male signaling to female signal playback, even if the disruptive signal amplitude was 10 dB lower than the female signal playback. CONCLUSION Although the mechanism underlying cessation of male signaling activity in the presence of disruption is not yet understood, results suggest that an 80 Hz vibrational signal should be tested in laboratory and field experiments to assess its efficacy in disrupting mating of GWSS.

The glassy-winged sharpshooter (GWSS), Homalodisca vitripennis, is an important vector of Xylella fastidiosa, the causal agent of Pierce’s disease of grapevine. GWSS control relies mainly on insecticides; therefore, an alternative method, such as vibrational mating disruption, is required. However, knowledge of GWSS intraspecific communication is necessary to evaluate applicability of such methods. Mating behavior and associated vibrational signals were described in different social contexts: individuals, pairs, and one female with two competing males. Behavioral analysis showed that GWSS mating communication involved the emission of three male and two female signals, with specific roles in two distinct phases of mating behavior, identification and courtship. Mating success depended on vibrational duets between genders, which were temporarily interrupted in the presence of male rivalry. Male rivalry behavior involved the emission of three distinct rivalry signals. Two rivalry signals resemble female signals and were associated with replacement of the female in the duet by the rival male. The third rivalry signal was emitted by competing males. Data suggested that rival males used mimicry and hostile signals to interrupt the ongoing duet and gain access to a female. In the future, knowledge acquired from this study will be essential to develop a mechanical mating disruption method for GWSS control.

Xylella fastidiosa (Wells) is a xylem-limited bacterium that causes Pierce’s disease of grapevines. The bacterium is transmitted by insect vectors such as the glassy-winged sharpshooter (GWSS), Homalodisca vitripennis (Germar). Experiments were conducted to compare the role of selected X. fastidiosa genes on 1) bacterial acquisition and retention in GWSS foreguts, and 2) transmission to grapevines by GWSS. Bacterial genotypes used were: mutants Xf-ΔpilG, Xf-ΔpilH, Xf-ΔgacA, and Xf-ΔpopP; plus wild type (WT) as control. Results showed that Xf-ΔpilG had enhanced colonization rate and larger numbers in GWSS compared with WT. Yet, Xf-ΔpilG exhibited the same transmission efficiency as WT. The Xf-ΔpilH exhibited poor acquisition and retention. Although initial adhesion, multiplication, and retention of Xf-ΔpilH in GWSS were almost eliminated compared with WT, the mutation did not reduce transmission success in grapevines. Overall, Xf-ΔgacA showed colonization rates and numbers in foreguts similar to WT. The Xf-ΔgacA mutation did not affect initial adhesion, multiplication, and long-term retention compared with WT, and was not significantly diminished in transmission efficiency. In contrast, numbers of Xf-ΔpopP were variable over time, displaying greatest fluctuation from highest to lowest levels. Thus, Xf-ΔpopP had a strong, negative effect on initial adhesion, but adhered and slowly multiplied in the foregut. Again, transmission was not diminished compared to WT. Despite reductions in acquisition and retention by GWSS, transmission efficiency of genotypes to grapevines was not affected. Therefore, in order to stop the spread of X. fastidiosa by GWSS using gene-level targets, complete disruption of bacterial colonization mechanisms is required.

Olive (Olea europaea) trees exhibiting leaf scorch or branch dieback symptoms in California were surveyed for the xylem-limited, fastidious bacterium Xylella fastidiosa. Only approximately 17% of diseased trees tested positive for X. fastidiosa by polymerase chain reaction, and disease symptoms could not be attributed to X. fastidiosa infection of olive in greenhouse pathogenicity assays. Six strains of X. fastidiosa were isolated from olive in Southern California. Molecular assays identified strains recovered from olive as belonging to X. fastidiosa subsp. multiplex. Pathogenicity testing of olive strains on grapevine and almond confirmed that X. fastidiosa strains isolated from olive yield disease phenotypes on almond and grapevine typical of those expected for subsp. multiplex. Mechanical inoculation of X. fastidiosa olive strains to olive resulted in infection at low efficiency but infections remained asymptomatic and tended to be self-limiting. Vector transmission assays demonstrated that glassy-winged sharpshooter (Homalodisca vitripennis) could transmit strains of both subspp. multiplex and fastidiosa to olive at low efficiency. Insect trapping data indicated that two vectors of X. fastidiosa, glassy-winged sharpshooter and green sharpshooter (Draeculacephala minerva), were active in olive orchards. Collectively, the data indicate that X. fastidiosa did not cause olive leaf scorch or branch dieback but olive may contribute to the epidemiology of X. fastidiosa-elicited diseases in California. Olive may serve as an alternative, albeit suboptimal, host of X. fastidiosa. Olive also may be a refuge where sharpshooter vectors evade intensive areawide insecticide treatment of citrus, the primary control method used in California to limit glassy-winged sharpshooter populations and, indirectly, epidemics of Pierce's disease of grapevine.

The glassy-winged sharpshooter (GWSS), Homalodisca vitripennis, is a generalist insect and a major pest of grapevines. GWSS is a vector of the bacterium Xylella fastidiosa, causal agent of Pierce’s disease that can lead to grapevine death within few years after infection. This chapter discusses the problem and current GWSS control methods. Then, the focus changes to efforts in developing a novel control method that uses synthetic vibrational signals to disrupt mating and, thus, population growth. A step-by-step method for creating effective playback signals is described and discussed. The method was termed “D.I.E.,” which stands for Describe, Identify, and Execute. The first step is to describe the basic biology of the insect pest with emphasis on communication behaviors. From there, one can begin identifying which candidate signals disrupt communication. Finally, execution tests are conducted to determine which signals effectively disrupt mating in laboratory, and more importantly, in the field. While there are still steps needed for large-scale implementation in the field, the basic biological questions related to whether synthetic vibrational signals can disrupt mating are answered affirmatively. The next direction will be to develop a mechanism of signal transmission across large areas. In addition, season long field trials are needed, taking into consideration natural insect movements into and out of treated areas.

A 5-year field study was conducted to evaluate effects of duration and exclusion of Xylella fastidiosa infections on young almond tree performance and their links to tree vigor. ‘Nemaguard,’ ‘Okinawa,’ ‘Nonpareil,’ and Y119 were used as rootstocks for almond scion ‘Sonora.’ Among X. fastidiosa-infected trees, there was significant etiological heterogeneity with i) absence of leaf scorching symptoms in the presence of reduced growth, ii) presence of leaf scorching symptoms in the absence of reduced growth, and iii) severe leaf scorching and reduced growth. Trunk cross sectional areas of X. fastidiosa-infected trees grafted on ‘Nemaguard’ and ‘Nonpareil’ rootstocks were significantly smaller than noninfected trees, whereas trunk size of trees grafted on ‘Okinawa’ and Y119 was not affected by infection status. Severity of leaf scorching symptoms was highest on trees grafted on ‘Nonpareil’ rootstock, intermediate on ‘Okinawa’ and Y119, and lowest on ‘Nemaguard.’ X. fastidiosa infections and seasonal leaf scorching symptoms persisted on most inoculated trees throughout the study, except on trees grafted on ‘Nemaguard’ that manifested complete leaf scorching symptom remission and apparent elimination of the pathogen after the second year. Results indicate that depending on rootstock type X. fastidiosa can affect trunk size in a relatively short period and/or persist for years as trees grow.

Pathogen spread by arthropod vectors is the outcome of pathogen-vector-plant interactions, as well as how these interactions are impacted by abiotic and biotic factors. While plant water stress impacts each component of the Pierce's disease pathosystem (Xylella fastidiosa Wells et al., insect vectors, and grapevines), the outcome of interactions in relation to pathogen spread is unknown. The objectives of this study were 1) to determine the role of plant water stress on vector acquisition and inoculation of X. fastidiosa under choice and no-choice conditions for source or recipient vines, and 2) to provide insights into the effects of vineyard irrigation regimes on spread of X. fastidiosa by using a host-vector epidemic model. Under no-choice conditions, pathogen acquisition increased as water stress increased in source plants, while inoculation was not affected by water status of recipient vines. Thus, under no-choice conditions, plant water stress increased transmission of X. fastidiosa. However, when vectors had a choice of an uninfected well-watered versus an infected water-stressed grapevine, transmission efficiency declined as water stress levels increased. While our experimental results produced wide uncertainty estimates, the epidemiological modeling suggested a non-linear relationship between water stress and pathogen spread: moderate water stress enhances pathogen spread but severe or no stress produce equivalent spread. In summary, both host plant condition and vector host preference interacted to determine transmission efficiency of X. fastidiosa.

The glassy-winged sharpshooter is an invasive insect capable of transmitting the plant pathogen Xylella fastidiosa. As rates of pathogen spread are a function of vector abundance, identification of factors contributing to glassy-winged sharpshooter egg production will aid in predicting population growth. Here, effects of stored energy reserves and adult diet on glassy-winged sharpshooter egg maturation were evaluated. To estimate energy reserves available to adult females at the beginning of feeding assays, residuals from a regression of wet weight on size were used. Analysis of a subset of females sacrificed at the beginning of feeding assays, demonstrated that females with a positive residual wet weight had higher lipid content and carried more eggs than females with a negative residual wet weight. To evaluate effects of diet and energy reserves on egg maturation, energy reserves available to females entering feeding assays on cowpea and grapevine were estimated. For females held on cowpea, residual wet weight and quantity of excreta produced over a 6-d feeding period affected egg production. In contrast, for females held on grapevine, only residual wet weight affected egg production. Comparison of cowpea and grapevine xylem sap determined that eight amino acids were more concentrated in xylem sap from cowpea than from grapevine. Collectively, the results suggest that glassy-winged sharpshooter population growth within crop monocultures will not depend solely on the nutritional quality of the specific crop for producing mature eggs but also on the quantity of energy reserves accumulated by females prior to entering that crop habitat.

Animal communication is a complex behavior that is influenced by abiotic and biotic factors of the environment. Glassy-winged sharpshooters (GWSS), Homalodisca vitripennis (Germar) (Hemiptera: Cicadellidae), primarily use vibrational signaling for courtship communication. Because GWSS is a major pest, transmitting the plant pathogenic bacterium Xylella fastidiosa Wells et al., interruption of communication is a possible avenue for control. Playback of white noise, pre-recorded female signals, and artificial female noise (continuously overlapping female signals) significantly reduced mating of GWSS when compared to silent control mating trials. Furthermore, to begin to determine the mechanism underlying playback control, female signaling activity was recorded in the presence of stimuli. In response to playback of female signals, females signaled (duet-like) more often than females tested in the absence of playback. After the first playback, almost two-thirds of females signaled a response within 3 s. Additionally, one-third of the females signaled within 1 s after cessation of white noise, and significantly more in the time periods following noise termination. Results highlight how GWSS responds to differing competitive disturbances in the environment and lays important ground work that possibly could be used to develop pesticide-free control methods.

Glassy-winged sharpshooter (GWSS), Homalodisca vitripennis (Germar), is a vector of the xylem-inhabitant bacterium Xylella fastidiosa Wells et al., which causes Pierce’s disease of grapevines. Current GWSS control strategies in California, USA include area-wide insecticide applications and mass release of mymarid egg parasitoids, including Gonatocerus ashmeadi Girault. Gas chromatography–mass spectrometry was used to identify ( E )-β-ocimene and ( E , E )-α-farnesene as volatiles emitted from grapevines on which GWSS had previously fed and oviposited. Attractiveness of female G. ashmeadi to sugar-based formulations containing either ( E )-β-ocimene, ( E , E )-α-farnesene, or a mixture of both was evaluated using Y-tube olfactometry. When exposed to synthetic formulation containing a mixture of ( E )-β-ocimene and ( E , E )-α-farnesene vs. blank control, 61% of G. ashmeadi females initially chose the synthetic formulation. After the initial choice for a Y-tube arm, females visited the Y-tube arm connected to the source of formulation more often than it did to the arm connected to a blank control. There was no difference in the female’s time spent in the arm connected to the formulation. When testing formulations containing either ( E )-β-ocimene or ( E , E )-α-farnesene alone, there was a 1:1 ratio between the proportion of parasitoid’s first choice, visits, and residence time. Results suggest that synthetic formulations containing mixtures of certain plant volatiles may be used to localize GWSS egg parasitoids in vineyard systems. Results are discussed in the context of potential applications in GWSS biological control programs.

Discovery of Xylella fastidiosa from olive trees with "Olive quick decline syndrome" in October 2013 on the west coast of the Salento Peninsula prompted an immediate search for insect vectors of the bacterium. The dominant xylem-fluid feeding hemipteran collected in olive orchards during a 3-mo survey was the meadow spittlebug, Philaenus spumarius (L.) (Hemiptera: Aphrophoridae). Adult P. spumarius, collected in November 2013 from ground vegetation in X. fastidiosa-infected olive orchards, were 67% (40 out of 60) positive for X. fastidiosa by polymerase chain reaction (PCR) assays. Euscelis lineolatus Brulle were also collected but tested negative for the pathogen. Transmission tests with P. spumarius collected from the Salento area were, therefore, conducted. After a 96-h inoculation access period with 8 to 10 insects per plant and a 30-d incubation period, PCR results showed P. spumarius transmitted X. fastidiosa to two of five periwinkle plants but not to the seven olive plants. Sequences of PCR products from infected periwinkle were identical with those from X. fastidiosa-infected field trees. These data showed P. spumarius as a vector of X. fastidiosa strain infecting olives trees in the Salento Peninsula, Italy.

Gonatocerus morrilli (Howard) (Hymenoptera: Mymaridae) is an egg parasitoid used in California, USA to control glassy-winged sharpshooter (GWSS), Homalodisca vitripennis (Germar) (Hemiptera: Cicadellidae). Virgin GWSS females deposit non-fertilized eggs and mated females can exhaust sperm reserves for egg fertilization. However, nothing is known about Gonatocerus spp. performance when using non-fertilized GWSS eggs as hosts. Host age preference for oviposition and suitability of non-fertilized GWSS eggs as hosts for G. morrilli reproduction were investigated to determine whether non-fertilized eggs on sentinel plants could be used to monitor egg parasitoid populations. Gonatocerus morrilli parasitized all ages of GWSS eggs (1–8 days old) regardless if the host egg was fertilized or not. In choice tests (fertilized versus non-fertilized eggs), parasitoids failed to emerge as adults from non-fertilized eggs more often than from fertilized eggs. The results indicate that non-fertilized eggs were accepted by G. morrilli as suitable hosts for oviposition, but were less suitable for immature development compared to fertilized eggs.

The glassy-winged sharpshooter, Homalodisca vitripennis (Germar) (Hemiptera: Cicadellidae), is a xylem fluid-ingesting leafhopper that transmits χylella fastidiosa Wells et al., a plant-infecting bacterium that causes several plant diseases in the Americas. Although the role of plant water stress on the population density and dispersal of H. vitripennis has been studied, nothing isknown about the effects of plant water stress on the transmission of χ. fastidiosa by H. vitripennis.Alaboratory study was conducted to determine the influence of plant water stress on the sharpshooter stylet probing behaviors associated with the acquisition and inoculation of χ. fastidiosa. Electrical penetration graph was used to monitor H. vitripennis feeding behaviors for 20-h periods on citrus [Citrus sinensis (L.) Osbeck] and almond [Prunus dulcis (Miller) D.A. Webb] plants subjected to levels of water stress. Adult H. vitripennis successfully located xylem vessels, then performed behaviors related to the evaluation of the xylem cell and fluid, and finally ingested xylem fluid from citrus and almond plants under the tested fluid tensions ranging from -5.5 to -33.0 bars and -6.0 to -24.5 bars, respectively. In general, long and frequent feeding events associated with the acquisition and inoculation of χ. fastidiosa were observed only in fully irrigated plants (i.e., >-10 bars), which suggests that even low levels of plant water stress may reduce the spread of χ. fastidiosa. Results provided insights to disease epidemiology and support the hypothesis that application of regulated deficit irrigation has the potential to reduce the incidence of diseases caused by χ. fastidiosa by reducing the number of vectors and by decreasing pathogen transmission efficiency.

Homalodisca vitripennis (Germar), a vector of Xylella fastidiosa, is associated with citrus plantings in California. Infested citrus orchards act as a source of vectors to adjacent vineyards where X. fastidiosa causes Pierce's disease. An analysis of the pattern and rate of movement of H. vitripennis and its egg parasitoid, Gonatocerus ashmeadi Girault, was conducted in a citrus orchard by using a protein mark-capture technique to quantify movement and net dispersal rates in the experimental areas. Treatments included irrigation at 100% of the crop evapotranspiration rate (ET(c)), 80, and 60% ET(c). Sex-specific net dispersal rates showed that H. vitripennis males and females moved consistently and contributed equally to the level of population change within treated areas. Trees irrigated at 60% ET(c) were the least preferred by H. vitripennis. Among all protein-marked individuals captured in the 60% ET(c) treatment, ≈ 75 and 88% in 2005 and 2006, respectively, were inflow individuals. Movement toward less preferable plants indicates that in agricultural landscapes dominated by perennial monocultures, there is a random component to H. vitripennis movement, which may result from the inability of H. vitripennis to use plant visual cues, olfactory cues, or both to make well-informed long-range decisions. The 80% ET(c) areas were a significant source of adult H. vitripennis and G. ashmeadi compared with the other treatments. Colonization rates by parasitoids were synchronized with the spatiotemporal distribution of H. vitripennis eggs. Results suggest that H. vitripennis movement from citrus into adjacent vineyards could be a result of random dispersal rather than oriented movement in response to host-plant characteristics.

Population structure of Homalodisca coagulata Virus-1 (HoCV-1) among and within field-collected insects sampled from a single point in space and time was examined. Polymorphism in complete consensus sequences among single-insect isolates was dominated by synonymous substitutions. The mutant spectrum of the C2 helicase region within each single-insect isolate was unique and dominated by nonsynonymous singletons. Bootstrapping was used to correct the within-isolate nonsynonymous:synonymous arithmetic ratio (N:S) for RT-PCR error, yielding an N:S value ~one log-unit greater than that of consensus sequences. Probability of all possible single-base substitutions for the C2 region predicted N:S values within 95% confidence limits of the corrected within-isolate N:S when the only constraint imposed was viral polymerase error bias for transitions over transversions. These results indicate that bottlenecks coupled with strong negative/purifying selection drive consensus sequences toward neutral sequence space, and that most polymorphism within single-insect isolates is composed of newly-minted mutations sampled prior to selection.

A study on seasonal abundance of Auchenorrhyncha species and their infectivity by Xylella fastidiosa in the Apulia region of Italy was conducted to identify ideal periods for monitoring and adoption of potential control measures against insect vectors. Adult populations of Auchenorrhyncha species were monitored monthly over a 2-yr period from five olive groves. A total of 15 species were captured, identified, and tested for presence of X. fastidiosa by polymerase chain reaction (PCR). For three species, Philaenus spumarius L., Neophilaenus campestris (Fallen), and Euscelis lineolatus Brulle, positive reactions to X. fastidiosa were obtained, on average, in 16.3, 15.9 and 18.4% of adult insects, respectively. Philaneous spumarius was the dominant species (39.8% of total Auchenorrhyncha captured) with the highest adult abundance in summer months. Adult P. spumarius and N. campestris were first detected between March and May in both years, and all insects tested during these periods (year 1: n = 42, year 2: n = 132) gave negative reactions to X. fastidiosa by PCR. Similarly, first adults of E. lineolatus that appeared from October to November (year 1: n = 20, year 2: n = 15) tested negative for presence of X. fastidiosa. Given the lack of transstadial and transovarial transmission of X. fastidiosa and considering that P. spumarius is univoltine, control measures against nymphal stages of P. spumarius should be investigated as means of population suppression to reduce spread of X. fastidiosa in olive groves.

A two-year study was conducted in a citrus orchard, Citrus sinensis L., to determine frequency of predation on glassy-winged sharpshooter (GWSS), Homalodisca vitripennis (Germar). A total of 1,578 arthropod predators, representing 18 taxa, were collected and assayed for the presence of GWSS egg protein by an enzyme-linked immunosorbent assay using a Homalodisca-species and egg-specific monoclonal antibody and then by polymerase chain reaction using a H. vitripennis-specific DNA marker. The gut content analyses revealed the presence of GWSS remains in the gut of 2.28 % of the total arthropod predator population, with 3.09 % of the spiders and 0.59 % of the insect predators testing positive. Moreover, a comparison of the two assays indicated that they were not equally effective at detecting GWSS remains in predator guts. Low frequencies of GWSS detection in the gut of predators indicated that GWSS are not a primary prey and that predators may contribute little to suppression of this pest in citrus.

Management of almond leaf scorch disease requires knowledge of all possible infection pathways. The disease is caused by the xylem-limited bacterium Xylella fastidiosa, which is transmitted by several species of sharpshooters. The objectives of this research were to elucidate the fate of bacteria in planta after inoculations in almond nursery plants and to determine patterns of insect vector population dynamics and temporal distribution of X. fastidiosa–infected plants relative to host plant assemblages in habitats surrounding commercial nurseries. In an experimental nursery, disease incidence was markedly affected by rootstock type. Prior to bud grafting, ‘Nemaguard’ rootstock seedlings were not susceptible to bacterial infection. After bud grafting with a susceptible scion (‘Sonora’), scions were susceptible to infection regardless of rootstock genotype. Surveys near commercial nurseries revealed that only habitats with permanent grass cover sustained vector populations throughout the season. A total of 87 plant samples tested positive for X. fastidiosa (6.3%) using enzyme-linked immunosorbent assay (ELISA), with a higher number of X. fastidiosa–infected plants found in weedy alfalfa fields than in other habitat types. Among plant species infected by X. fastidiosa, 33% were winter annuals, 45% were biennials or perennials, and 22% were summer annuals. Collectively, these findings identified a potential pathway for X. fastidiosa infection of almonds in nursery situations.

Methyl bromide (MB) chamber fumigations were evaluated for postharvest control of spotted wing drosophila (SWD), Drosophila suzukii, in strawberry exports from California USA. Strawberries were infested with the most MB-tolerant age of SWD (60‐ to 108-h old at fumigation, ca. mature larvae), infested fruit were buried amongst uninfested fruit in export packaging, and fumigations were with 48 mg L− 1 (3.0 lbs/1000 ft3) for 3 h at 18.0 ± 0.5 °C ( x ¯ ± s ). Complete mortality of 105,173 ± 3,321 (n ± s) SWD specimens was achieved with applied doses ≥ 34.5 mg L− 1 and exposures, expressed as a concentration × time products (CTs), ≥ 80.3 mg L− 1 h.

Homalodisca vitripennis (Germar) (Hemiptera: Cicadellidae) is an invasive vector of Xylella fastidiosa, the causal agent of Pierce's disease of grapevines (Vitis vinifera L.). Transmission efficiency of X. fastidiosa to grapevines by H. vitripennis originating from two geographically separated populations in California (Riverside and Bakersfield) based on gender and age was evaluated. To evaluate transmission efficiencies among groups, insects were given a 96-h acquisition access period on infected grapevines and caged in groups of five on healthy grapevines for a 72-h inoculation access period. At the conclusion of tests, polymerase chain reaction determined that a mean ± SD of 0.98 ± 1.02 X. fastidiosa-positive H. vitripennis were present on each grapevine and that 29% of test plants were infected. Acquisition and retention of X. fastidiosa was not affected by vector origin, gender, or age. The probability that a grapevine was infected 12 wk after the inoculation access period increased with the number of X. fastidiosa-positive H. vitripennis per plant. Gender had no effect on inoculation success and main effects of insect origin and age on inoculation success were minor. Collectively, the result indicated that H. vitripennis origin, gender, and age did not affect acquisition and retention of X. fastidiosa and had only minor effects on inoculation success under laboratory conditions. Accordingly, rates of pathogen spread in the field are more likely to be affected by local biotic and abiotic factors that differentially affect H. vitripennis abundance and movement based on origin, gender, and age than inherent differences in transmission efficiencies among these groups.

Honeydew from phloem-feeding insects and fruit fly insecticidal baits may serve as adult food resources for some insect species. In California (USA) olive orchards, the black scale [Saissetia oleae (Olivier) (Hemiptera: Coccidae)] is a common honeydew producer, and spinosad-based fruit fly bait (GF-120) is used to control the olive fruit fly [Bactrocera oleae (Rossi) (Diptera: Tephritidae)]. We investigated the effects of black scale honeydew and GF-120, as food resources, on adult foraging behaviour and survival of the olive fruit fly and two parasitoids in the olive agroecosystem: Scutellista caerulea (Fonscolombe) (Hymenoptera: Pteromalidae), a natural enemy of black scale, and Psyttalia humilis (Silvestri) (Hymenoptera: Braconidae), a parasitoid of the fruit fly. In food choice tests, female flies did not show a preference between GF-120 bait and honeydew, whereas male flies and the parasitoids we tested preferred honeydew. Adults of the three insect species readily fed on honeydew, but the natural enemies never (P. humilis) or rarely (S. caerulea) fed on GF-120 bait. Olfactometer tests further confirmed that the tested natural enemies were not attracted to GF-120 bait. The presence of honeydew significantly reduced fruit fly mortality when both honeydew and GF-120 were provided, compared with GF-120 given alone. A single meal of honeydew increased longevity in all insect species tested. The mean longevities of honeydew-fed insects were not significantly different from those feeding on clover honey. Our results suggest that the presence of honeydew would benefit the three insect species and may reduce the efficacy of GF-120 for fruit fly control because of preference of honeydew rather than fruit fly bait as a food resource.

The glassy-winged sharpshooter, Homalodisca vitripennis (Germar), is native to the southeastern United States and northeastern Mexico. It was detected in southern California in the late 1980s and in the San Joaquin Valley in 1999, where it transmits the bacterium Xylella fastidiosa to grapevines and other crops. The reproductive success of hybrid and pure line H. vitripennis from two geographically separated populations in California (Riverside (RIV) and Bakersfield (BAK)) was evaluated under identical conditions. The RIV and BAK populations had different preoviposition periods that persisted through the second generation of each lineage. From adult molt, the preoviposition period in both female generations was significantly shorter for RIV (F 0 = 28.2 days and F 1 = 62.3 days) than BAK females (F 0 = 46.1 days and F 1 = 170.4 days). After a 21-day mating period, F 0 and F 1 females deposited on average 391 (range, 21–967) and 196 (range, 0–755) eggs, respectively, without significant differences in fecundity among the F 0 and F 1 mating pair treatments. Egg accumulation rates among F 1 treatments showed that females in the RIV groups rapidly deposited their eggs within the first 120 days after adult molt while BAK females maintained a steady accumulation rate during their life. The performance of both hybrid lines was intermediate between the pure lineages. The F 0 mating pairs: ♀RIV × ♂RIV, ♀RIV × ♂BAK, ♀BAK × ♂RIV, and ♀BAK × ♂BAK produced on average 185, 94, 79, and 0 viable eggs, respectively, which suggested a delayed sexual maturity of BAK males and females. The proportion of viable eggs deposited decreased gradually, which suggests that females completely exhausted sperm reserves. From a management perspective, delayed reproductive maturity and polyandry are weak links in H. vitripennis ’ biology that may be exploited through mating disruption or insect sterilization strategies to reduce population growth and augment pressure by natural enemies.

The glassy-winged sharpshooter, Homalodisca vitripennis (Germar), vectors the bacterium Xylella fastidiosa that induces Pierce's disease of grape. This study determined the effect of temperature on the feeding activity of H. vitripennis adults and the resulting production of excreta. The Logan type I model described a nonlinear pattern that showed excreta production increased up to an optimal temperature (33.1°C), followed by an abrupt decline near an estimated upper threshold (36.4°C). A temperature threshold for feeding, at or below which adults cease feeding, was estimated to be 10°C using a linear regression model based on the percentage of adults producing excreta over a range of constant temperatures. A simulated winter-temperature experiment using fluctuating thermal cycles confirmed that a time period above the temperature threshold for feeding was a critical factor in determining adult survival. Using data from the simulated temperature study, a predictive model was constructed by quanti...

The agricultural pest, glassy-winged sharpshooter (GWSS), Homalodisca vitripennis, relies primarily on successful vibrational communication across its home plant. Males and females engage in a vibrational duet to identify correct species, attractiveness of mate, and location on the plant. The signal produced by these animals has a dominant frequency component between 80 and 120 Hz, with harmonics spaced approximately 100 Hz apart. However, our analysis revealed that not all harmonics are present in every recorded signal. Therefore, we sought to understand how the GWSS vibrational communication signal changes over distance on the plant. We have confirmed that first, with increasing distance fewer high frequency harmonics are present. Second, at distances of only 50 cm, there is a difference in the latency of signal arrival based on the frequency, with higher frequencies arriving sooner. Finally, the animal appears to generate no airborne signal component, yet, the low frequencies are clearly detectable in neighboring plants by the signal “jumping” from leaf-to-air-to-leaf. Together, these results highlight the complexity of vibration transmission in plants and the possibility of alteration and disruption of the GWSS signal.

Anagrus epos Girault (Hymenoptera: Mymaridae) is a natural enemy candidate for a classical biological control program targeting the glassy-winged sharpshooter (GWSS), Homalodisca vitripennis (Germar) (Hemiptera: Cicadellidae), in California. Little is known about the biology or ecology of A. epos when it utilizes GWSS eggs as a host. Here, we report the results of laboratory studies that describe the host age preference for oviposition, longevity of A. epos adults provided with different food sources, and developmental rates at six different constant temperature regimes. Anagrus epos is a gregarious parasitoid in GWSS eggs with up to 14 adults emerging from each GWSS egg. In choice and no-choice tests for oviposition, A. epos females successfully parasitized all developmental ages of GWSS eggs (1–8 days old). In choice tests, parasitism rates were significantly higher in 1-, 3-, 4-, and 5-day-old GWSS eggs than in 2-, 6-, 7-, and 8-day-old eggs. If provided with honey and water, honey only, water only, or no food or water, A. epos females lived on average 8.2, 4.7, 2.6, and 1.6 days, respectively. Anagrus epos required 294.1 degree-days above a lower temperature threshold of 12.4 °C to develop from egg to adult (eclosion). Our results provide baseline information useful in the development of an efficient parasitoid mass rearing program for A. epos release and evaluation in California.

Gonatocerus ashmeadi Girault is an egg parasitoid with potential use in glassy-winged sharpshooter (GWSS), Homalodisca vitripennis (Germar), biological control in California. We tested the hypotheses that (1) G. ashmeadi uses chemical volatiles as cues to find hosts, (2) its success in host finding varies among plant species, and (3) the release of semiochemicals is systemically induced by GWSS feeding and oviposition. Using a glass Y-tube olfactometer, we determined G. ashmeadi’s preference for volatiles of infested versus uninfested lemon, grapevine, red-tip photinia, and crape myrtle plants. The parasitoid’s first choice to, its residence time, and the number of visits per Y-tube arm were used to assess its plant choice. G. ashmeadi chose the infested lemon, red-tip photinia, or grapevine plant significantly more often (62%, 67%, and 63%, respectively) than uninfested hosts, whereas they chose infested and uninfested crape myrtle equally often (49%). Females spent more time in and made more visits to the olfactometer arm connected to the infested plant than to the arm connected to the uninfested plant, except when testing crape myrtle. When testing for a systemic plant response to GWSS infestation, only infested lemon was significantly more attractive to the parasitoids than was an uninfested plant. These results suggest that G. ashmeadi females use chemical volatiles as cues to find GWSS egg masses and that host finding success varies among GWSS host plants. Some plants used by GWSS as oviposition hosts may serve as an escape from parasitization by G. ashmeadi and act as reservoirs for new GWSS individuals.

Controlling navel orangeworm, a key pistachio pest, is problematic because the moth overwinters in “mummy” nuts. After harvest, there may be more than 30,000 pistachio nuts (mummies) left behind per acre. To provide better information for winter sanitation decisions, we investigated the number of available mummies and their levels of navel orangeworm infestation from winter through early summer in California pistachio orchards. Navel orangeworm mortality was highest from late December through mid-February, and was also higher on the ground than in trees. Mortality on the ground was highest when mummies were tilled or mowed with the groundcover than when nuts were left on the raised berm. Our data indicates that, in contrast to almonds, it is more productive to focus on clearing pistachios from the ground than on removing them from trees. However, winter sanitation procedures also should be augmented in order to destroy more overwintering navel orangeworm.