Glassy-winged Sharpshooter Research Articles

Engineering Enemy-free Space: An Invasive Pest that Kills its Predators

The biological invasion of the glassy-winged sharpshooter, Homalodisca coagulata, into French Polynesia presents a novel threat to Pacific Island ecosystems. Widely known as an agricultural pest because of its role as a vector of numerous lethal plant diseases, H. coagulata may pose a substantial and immediate risk to arthropod predators on invaded islands in French Polynesia. Controlled feeding experiments revealed that island spiders can be killed following predation on H. coagulata. Spider mortality appeared to result from lethal intoxication, although no form of chemical defense has been reported in H. coagulata. In the two spider species tested, approximately half of all individuals that attacked H. coagulata nymphs or adults died. As populations of this insect increase in size and range on invaded islands in French Polynesia, H. coagulata will increasingly encounter these and other arthropod predators, raising the possibility of population-level impacts on susceptible predator species. Field surveys of island spiders across nine sites on H. coagulata-invaded and H. coagulata-uninvaded islands suggest that this insect may already have adversely impacted an endemic spider on at least one island. Work is needed to identify the nature of the lethal agent harbored within H. coagulata and the taxonomic and geographic breadth of predators vulnerable to it. The generality of H. coagulata-lethality and the capacity of afflicted predator species for population-level adaptation or learned avoidance in response to this spreading pest will determine the magnitude of the threat H. coagulata poses in the South Pacific.

Profiling transcriptional changes in Citrus sinensis (L.) Osbeck challenged by herbivory from the xylem-feeding leafhopper Homalodisca coagulata (Say) by cDNA macroarray analysis

The molecular mechanisms underlying plant defense to sap-feeding insects are slowly being uncovered. In large part, past research has focused on interactions between phloem-feeding insects and their annual host plants with little emphasis on xylem-feeders or woody perennials—especially fruit trees. Using nylon filter cDNA arrays, we analyzed the transcriptional changes of 1731 non-redundant citrus transcripts that resulted from herbivory by a xylem-feeding leafhopper, the glassy-winged sharpshooter (GWSS), Homalodisca coagulata (Say) (Hemiptera: Cicadellidae). In addition, herbivory-elicited changes were compared to those of mechanical damage to better identify GWSS-specific responses. GWSS feeding led to a significant expression change in 50 transcripts. Of these, 14 were also changed by mechanical damage; however, the magnitude was in many cases reduced, suggesting transcriptional modification by GWSS-derived elicitors. Sequence similarity searches with the public database GenBank indicated that the responsive transcripts broadly function in direct defense, defense signaling, ROS scavenging, transport, cell wall modification, photosynthesis and abiotic stress. In particular, GWSS feeding resulted in a transcript profile that resembled wounding, likely through jasmonic acid-independent pathways, as well as an association with dehydration stress. In contrast to similar studies with aphids, salicylic acid-dependent pathogenesis-elated genes were weakly induced. Interestingly, six of the GWSS-responsive transcripts failed to significantly match any public protein sequence signifying their potential as novel genes functioning in plant defense, wound response or abiotic stress.

Development and application of a glassy-winged and smoke-tree sharpshooter egg-specific predator gut content ELISA

Abstract The recent invasion of southern California by the glassy-winged sharpshooter (GWSS), Homalodisca coagulata (Say) (Hemiptera: Cicadellidae), has triggered a statewide control effort. Management of GWSS will include biological control using resident and imported natural enemies. Currently, very little information is available on the role of generalist predators in suppression of GWSS eggs, nymphs or adults. We have developed a sharpshooter egg-specific monoclonal antibody (MAb) for use as a diagnostic tool for predator gut content analysis. The MAb was tested by an indirect enzyme-linked immunosorbent assay (ELISA) for specificity to the different life stages of GWSS, smoke-tree sharpshooter (STSS), Homalodisca liturata Ball (Hemiptera: Cicadellidae), and various life stages of 27 other arthropod species. We found that the MAb only reacted to the egg stage of both sharpshooters and, to a lesser extent, to the adult stage of gravid GWSS and STSS females. Moreover, the ELISA was more responsive to younger GWSS eggs than older ones. Laboratory trials were conducted to determine how long GWSS egg antigen remained detectable in the guts of the green lacewing, Chrysoperla carnea Stephens (Neuroptera: Chrysopidae) and the ladybird beetle, Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) using both an indirect and sandwich ELISA format. We found that GWSS egg antigen was detectable for up to 30 and 12 h in the guts of C. carnea and H. axyridis; respectively, and that the sandwich ELISA was much more sensitive than the indirect ELISA. Finally, 98 field-collected lacewings were examined for sharpshooter remains using our sharpshooter-specific sandwich ELISA. The assay detected sharpshooter egg antigen in 8.2% of the lacewings examined. This work represents a first step towards identifying the GWSS predator complex.

Establishment of Baseline Susceptibility Data to Various Insecticides for <I>Homalodisca coagulata</I> (Homoptera: Cicadellidae) by Comparative Bioassay Techniques

Homalodisca coagulata Say, adults from three locations in California were subjected to insecticide bioassays to establish baseline toxicity. Initially, two bioassay techniques, petri dish and leaf dip, were compared to determine the most useful method to establish baseline susceptibility data under laboratory and greenhouse conditions. Comparative dose-response data were determined by both techniques to endosulfan, dimethoate, cyfluthrin, and acetamiprid. Toxic values were similar to some insecticides with both techniques but not for all insecticides, revealing susceptibility differences among the three populations of H. coagulata. In subsequent tests, the petri dish technique was selected to establish baseline susceptibility data to various contact insecticides. A systemic uptake bioassay was adapted to estimate dose-mortality responses to a systemic insecticide, imidacloprid. A 2-yr comparison of toxicological responses showed all three populations of H. coagulata to be highly susceptible to 10 insecticides, including chlorpyrifos, dimethoate, endosulfan, bifenthrin, cyfluthrin, esfenvalerate, fenpropathrin, acetamiprid, imidacloprid, and thiamethoxam. In general, two pyrethroids, bifenthrin and esfenvalerate, were the most toxic compounds, followed by two neonicotinoids, acetamiprid and imidacloprid. The LC50 values for all insecticides tested were lower than concentrations used as recommended field rates. Baseline data varied for the three geographically distinct H. coagulata populations with the petri dish technique. Adult H. coagulata collected from San Bernardino County were significantly more susceptible to select pyrethroids compared with adults from Riverside or Kern counties. Adults from San Bernardino County also were more sensitive to two neonicotinoids, acetamiprid and imidacloprid. The highest LC50 values were to endosulfan, which nonetheless proved highly toxic to H. coagulata from all three regions. In the majority of the tests, mortality increased over time resulting in increased susceptibility at 48 h compared with 24 h. These results indicate a wide selection of highly effective insecticides that could aid in managing H. coagulata populations in California.

Competition between Gonatocerus ashmeadi and G. triguttatus for glassy winged sharpshooter (Homalodisca coagulata) egg masses

The introduction of a biological control agent can have significant effects on natural enemies that use the same host. Interspecific competition between natural enemies can impact the efficacy of control and, consequently, is the subject of increasing research scrutiny. Three experimental approaches were used to evaluate competitive outcomes between Gonatocerus ashmeadi and G. triguttatus parasitizing Homalodisca coagulata egg masses in the laboratory. (1) When both species were introduced to high densities of host eggs 1, 3 and 5 days of age, mean percentage offspring was significantly higher for G. ashmeadi offspring (23.2% greater than G. triguttatus). (2) When a female parasitoid of each species was offered a single egg mass, offspring production was statistically similar for the two species. Gonatocerus triguttatus showed aggressive behavior, although this only accounted for 0.8% of the female's total foraging time and did not lead to proportionately higher offspring production. (3) Regardless of order, more G. triguttatus offspring (up to 96%) emerged than G. ashmeadi offspring when one female was introduced sequentially to one egg mass. The relative success in offspring production was affected primarily by the sequence in which the parasitoids were introduced, and to a lesser extent by the interval between successive parasitoid introductions, and the age of the egg mass. These results illustrate the importance of experimental design in the assessment of competitive superiority between two species of parasitoids. Improper experimental design can lead to contradictory outcomes in laboratory-based competition studies due to the interplay of extrinsic and intrinsic competitive behavior. Biological control practitioners need to be aware of the complexity of competitive behavior when designing pre-introduction laboratory tests to determine a priori which natural enemy from several candidate species is likely to be the most effective agent at controlling the target.

Establishment of Baseline Susceptibility Data to Various Insecticides for Homalodisca coagulata (Homoptera: Cicadellidae) by Comparative Bioassay Techniques

Establishment of Baseline Susceptibility Data to Various Insecticides for Homalodisca coagulata (Homoptera: Cicadellidae) by Comparative Bioassay Techniques

Correlation of stylet activities by the glassy-winged sharpshooter, Homalodisca coagulata (Say), with electrical penetration graph (EPG) waveforms

Glassy-winged sharpshooter, Homalodisca coagulata (Say), is an efficient vector of Xylella fastidiosa ( Xf), the causal bacterium of Pierce's disease, and leaf scorch in almond and oleander. Acquisition and inoculation of Xf occur sometime during the process of stylet penetration into the plant. That process is most rigorously studied via electrical penetration graph (EPG) monitoring of insect feeding. This study provides part of the crucial biological meanings that define the waveforms of each new insect species recorded by EPG. By synchronizing AC EPG waveforms with high-magnification video of H. coagulata stylet penetration in artifical diet, we correlated stylet activities with three previously described EPG pathway waveforms, A1, B1 and B2, as well as one ingestion waveform, C. Waveform A1 occured at the beginning of stylet penetration. This waveform was correlated with salivary sheath trunk formation, repetitive stylet movements involving retraction of both maxillary stylets and one mandibular stylet, extension of the stylet fascicle, and the fluttering-like movements of the maxillary stylet tips. Waveform B1 was ubitquious, interspersed throughout the other waveforms. B1 sub-type B1w was correlated with salivation followed by maxillary tip fluttering. This tip fluttering also occurred before and during B1 sub-type B1s, but was not directly correlated with either the occurrence or frequency of this waveform. Waveform B2 was correlated with sawing-like maxillary stylet movements, which usually occurred during salivary sheath branching. Waveform C was correlated with ingestion. Fluid outflow was also observed as a mechanism to clear the maxillary tips from debris during waveform C. This detailed understanding of stylet penetration behaviors of H. coagulata is an important step toward identifying the instant of bacterial inoculation which, in turn, will be applied to studies of disease epidemiology and development of host plant resistance.

Invasion of French Polynesia by the Glassy-Winged Sharpshooter, Homalodisca coagulata (Hemiptera: Cicadellidae): A New Threat to the South Pacific

The glassy-winged sharpshooter, Homalodisca coagulata (Say), is a major pest of agricultural, ornamental, and native plants. It is native to the southeastern United States and northeastern Mexico. Homalodisca coagulata was first recorded in Tahiti (French Polynesia) in 1999. It reproduced and spread rapidly in French Polynesia and is currently found in almost all islands in the Society Islands group (Tahiti, Moorea, Raiatea, Huahine, Bora Bora, Tahaa, Maupiti), in Nuku Hiva in the Marquesas, and in Tubuai and Rurutu in the Australs. Tahiti and Moorea are the most heavily infested islands, where H. coagulata populations have reached densities far exceeding those observed in California (this pest invaded California in the late 1980s) or in its native range. Major factors responsible for high population densities of H. coagulata in French Polynesia are permissive environmental conditions (mild climate and abundant year-round feeding and oviposition substrates), absence of host-specific natural enemies, intoxication of generalist predators that attack nymphal and adult stages, and limited competition for resources. Homalodisca coagulata causes several problems in French Polynesia: dripping excreta from high densities of feeding adults and nymphs affect outdoor recreation under trees and create a social nuisance, attraction of large numbers of flying adults to lights at night and collisions with people are severe annoyances, and large numbers of H. coagulata feeding on plants can cause impaired growth. The major concern for French Polynesia is the possibility of this pest acquiring and vectoring the lethal plant bacterium Xylella fastidiosa, which could have a disastrous impact on ornamental, agricultural, and native plants. Surveys are currently under way to detect X. fastidiosa in French Polynesia. Presence of large populations of H. coagulata in French Polynesia presents a major threat to agriculture and the biodiversity of South Pacific countries because this insect has clearly demonstrated a high invasion potential.

Uptake and persistence of imidacloprid in grapevines treated by chemigation

The uptake and persistence of a systemic formulation (240 g l −1 SC) of imidacloprid was studied in grapevines treated by chemigation, with the objective of defining suitable application rates for control of the glassy-winged sharpshooter Homalodisca coagulata Say. The sharpshooter is an important vector of Pierce's Disease in southern California, and insecticide treatments are necessary for effective management of insect populations and disease transmission. Uptake of imidacloprid was most rapid at the highest rates of application (281 and 562 g ha −1), reaching target threshold levels within the xylem fluid of 10 μg l −1 within 2 days in younger vines (4 years old). At 141 g ha −1, however, uptake was slow and threshold levels were not achieved in every vine. In older vines (20 years old), 6–8 days elapsed before threshold levels were detected in vines treated with 281 and 562 g ha −1. Despite the initial delay in uptake, once the target threshold was reached, it was maintained throughout the season. It is clear from available information on the population dynamics of the glassy-winged sharpshooter, particularly relating to its seasonal movement from citrus orchards to neighboring vineyards, that appropriate timing of insecticide treatments can play a crucial role in the management of this pest.

Parasitism of the glassy-winged sharpshooter, Homalodisca coagulata (Homoptera: Cicadellidae): Functional response and superparasitism by Gonatocerus ashmeadi (Hymenoptera: Mymaridae)

Abstract The functional response by the egg parasitoid, Gonatocerus ashmeadi, and superparasitism of Homalodisca coagulata eggs were found to be related to host age and density when studied under laboratory conditions. Several aspects relating to parasitism of 1-, 3-, 5-, 7-, 9-day-old H. coagulata eggs were measured under varied densities ranging from 1:1 to 1:60 parasitoid to host ratios. The functional response for the parasitoid to host eggs of all age groups closely fit the Type II model that describes responses to changing densities. The instantaneous attack rate and handling time of the parasitoid were similar for H. coagulata eggs of various ages. The number of host eggs parasitized varies significantly with host density and age, but not when analyzed by a host age × density interaction. However, host age and density, as well as the host age × density interaction, contribute significantly to the differences found in length of the development time of G. ashmeadi within host eggs. This parasitoid showed a significantly greater tendency toward superparasitism at parasitoid-to-host ratios ⩽10:100. The maximum number of parasitoid eggs found in a single host egg was 18. The frequencies of superparasitism for G. ashmeadi display a random distribution over all observed host densities. Our results also suggest G. ashmeadi eliminates the supernumerary parasitoids through physiological suppression.

Phenology and demography of Homalodisca coagulata (Hemiptera: Cicadellidae) in southern California citrus and implications for management

Populations of Homalodisca coagulata (Say) were sampled from citrus orchards in southern California, USA to characterize and quantify seasonal occurrences of nymphs and adults with the goal of identifying management opportunities through well-timed treatments and/or natural enemy releases. Higher densities of H. coagulata in 2001 contributed to a complete seasonal profile that began in early spring with the emergence of first instar nymphs and their progression through five nymphal instars lasting until mid-August. Adult emergence began in mid-June with peak adult densities attained from mid to late August followed by a gradual decline through autumn. A persistent and significant male bias was observed in the adult sex ratio from the time of first emergence through mid-October in oranges; the same trend was present in lemons, but with more variability. Adult densities gradually declined through the winter months into the following spring before rapidly increasing again in June as the 2002 spring generation of nymphs began emerging as adults. The seasonal timing of nymphs and adults in 2002 was nearly identical to that observed the previous year. Phenology data from both years were incorporated into a stochastic, temperature-dependent model that predicts the occurrences of H. coagulata stages through time. Applications of imidacloprid early in the spring generation of nymphs proved very effective at reducing nymphs and sustaining lower densities of adults through summer.

Mitochondrial DNA variation among populations of the glassy-winged sharpshooter, Homalodisca coagulata

Mitochondrial DNA variation among populations of the glassy-winged sharpshooter, Homalodisca coagulata

Spatial and temporal distributions of two sympatric Homalodisca spp. (Hemiptera: Cicadellidae): Implications for areawide pest management

Four-year landscape-scale monitoring was conducted to investigate dynamics of the spatial and temporal distributions of Homalodisca coagulata and H. liturata and their spatial associations with the surrounding vegetation. Temporal trap catches of H. liturata and H. coagulata showed two peaks per year, and the peaks of the two species coincided. Spatial analysis with distance indices (SADIE) showed that spatial distributions of each species were significantly consistent between years. All patches (i.e. clusters of significantly high trap catches) of H. coagulata were located near citrus, and no patch was found in urban landscapes. Major patches of H. liturata and major gaps (i.e. clusters of significantly lower trap catches) of H. coagulata were located in desert saltbush scrub and urban areas, resulting in negative spatial association between the two species. Between-year spatial consistency of H. coagulata and H. liturata and their spatial relationship with the surrounding vegetation implies that areawide management targeting specific areas would be possible by identifying the patches and gaps of H. coagulata and H. liturata in space and time.

Stylet Penetration by Adult <I>Homalodisca coagulata</I> on Grape: Electrical Penetration Graph Waveform Characterization, Tissue Correlation, and Possible Implications for Transmission of <I>Xylella fastidiosa</I>

The sharpshooter Homalodisca coagulata (Say) (Hemiptera: Cicadellidae: Cicadellinae) is an exotic vector of the Pierce’s disease (PD) bacterium, Xylella fastidiosa (Wells et al.), that was first observed in California in 1989. H. coagulata has since greatly increased the threat of PD to the grape industry as well as stone fruit, nursery, and ornamental industries in California. This is the first in a series of articles that together describe how sharpshooter stylet penetration behaviors (especially intricate stylet activities, salivation, and ingestion) control transmission (i.e., acquisition and inoculation) of X. fastidiosa. Herein, we categorized and characterized alternating current electrical penetration graph (EPG) waveforms from glass-winged sharpshooter stylet penetration on petiole of susceptible grape (‘Cabernet Sauvignon’), paying special attention to waveform fine structures that are likely to be the key to detecting the instant of inoculation. We also correlated waveforms with salivary sheath termini in grape tissues. For the first time in any EPG study of leafhopper or planthopper feeding, we demonstrate through case studies of individual probes how to follow the process of stylet penetration step by step as it is occurring, including salivary sheath branching and when the stylets first puncture a xylem cell. Finally, we discuss the implications of our findings for understanding the transmission mechanism of X. fastidiosa, in comparison with hypothesized mechanisms in the literature.

Vector Transmission of <I>Xylella fastidiosa</I>: Applying Fundamental Knowledge to Generate Disease Management Strategies

Xylella fastidiosa is a xylem-limited bacterium transmitted to plants by xylem sap-feeding insects. This pathogen has a wide host range, causing disease in crops such as grape, citrus, almond, and coffee; ornamental plants; and trees. Sharpshooter leafhoppers are the major vectors of X. fastidiosa to crops of economic importance. Transmission characteristics include the lack of a latent period, no transstadial or transovarial transmission, persistence in adults, and multiplication in the foregut of vectors. Various factors influence vector transmission of X. fastidiosa, including the distribution and density of bacterial populations in host plants, insect host range and plant preference, season of inoculation, and climatic conditions. The ecology of vectors can affect epidemics, as demonstrated by the large increase in Pierce’s disease of grapevine incidence in California after the introduction of Homalodisca coagulata (Say). Disease control strategies should incorporate basic knowledge of transmission biology, vector ecology, and other interactions involved in X. fastidiosa diseases. We discuss basic aspects of X. fastidiosa transmission by vectors, the ecology of insects in relation to transmission and disease spread, and how basic research can be applied to the development of management strategies for a X. fastidiosa disease.

<I>Homalodisca coagulata</I> (Hemiptera: Cicadellidae) Feeding Posture

The sharpshooter Homalodisca coagulata Say (Hemiptera: Cicadellidae) is a polyphagous insect that feeds primarily from the xylem vessels of host plants. This insect is an efficient vector of the xylem-limited, plant-pathogenic bacterium Xylella fastidiosa Wells, which is the causal agent of several important diseases in ornamental and agricultural crops. In wild populations, H. coagulata have been observed to almost exclusively orient with their anterior facing toward the roots (AFR), regardless of branch position. The orientation of H. coagulata seemed to be chosen before stylet insertion. Neither masking plant chemical and morphological surface cues nor placing test plants in the absence of light affected body posture. The introduction of 1.5-V direct current electricity to the plants resulted in altered body positioning. Removal of both front tarsi influenced body position; however, removal of only the right or left front tarsi had no effect on H. coagulata body position. Removal or masking of right, left, or both antennae resulted in altered body position.

Introduced parasitic wasps could control glassy-winged sharpshooter

The glassy-winged sharpshooter (GWSS) is an introduced pest that spreads the bacterium Xylella fastidi-osa, which causes a variety of diseases such as Pierce's disease in grapevines and leaf scorch in oleanders. GWSS has been established in Southern California since about 1990 and has also successfully invaded French Polynesia, Hawaii and Easter Island. Researchers from UC, the U.S. Department of Agriculture and the California Department of Food and Agriculture have introduced parasitic wasps for the biological control of GWSS. Four parasitoids from the southeastern United States have been released and appear to be establishing in Southern California. Parasitoids from Argentina are also being evaluated in quarantine but have not yet been released.

Impact of a Screen Barrier on Dispersion Behavior of <I>Homalodisca coagulata</I> (Hemiptera: Cicadellidae)

The recent incursion of the sharpshooter Homalodisca coagulata (Say) (Hemiptera: Cicadellidae), a vector of the plant pathogenic bacterium Xylella fastidiosa, into southern California has caused new epidemics of plant diseases. The potential of H. coagulata to spread throughout the state and disseminate disease has encouraged the development of techniques to limit further spread of the vector and to manage disease epidemics where the insect already exists. We evaluated a unique tactic to curtail the immigration of H. coagulata into high-value crops, including nursery stock, where they can be spread via commercial transportation throughout the state and into disease-susceptible vineyards. This tactic consists of a 5-m-high screen barrier surrounding the crop that is impenetrable to H. coagulata. We examined H. coagulata orientation and flight direction when placed near or on the screen barrier, and determined the proportion of insects that flew over it. When released midway between a barrier and adjacent vegetation 71.5% of H. coagulata flew away from the barrier and in the direction of the vegetation; whereas 29.5% flew in the direction of the barrier. Of the total number of H. coagulata released, 7.5% flew over the barrier. When placed on the barrier, H. coagulata generally climbed up an average of 1.16 m before flying away from the structure. Of the total number of H. coagulata placed on the barrier, 6% flew over it. These results suggest that a screen barrier can be a part of a management strategy to reduce number of H. coagulata in high-value crops.

Impact of a Screen Barrier on Dispersion Behavior of Homalodisca coagulata (Hemiptera: Cicadellidae)

The recent incursion of the sharpshooter Homalodisca coagulata (Say) (Hemiptera: Cicadellidae), a vector of the plant pathogenic bacterium Xylellafastidiosa, into southern California has caused new epidemics of plant diseases. The potential of H. coagulata to spread throughout the state and disseminate disease has encouraged the development of techniques to limit further spread of the vector and to manage disease epidemics where the insect already exists. We evaluated a unique tactic to curtail the immigration of H. coagulata into high-value crops, including nursery stock, where they can be spread via commercial transportation throughout the state and into disease-susceptible vineyards. This tactic consists of a 5-m-high screen barrier surrounding the crop that is impenetrable to H. coagulata. We examined H. coagulata orientation and flight direction when placed near or on the screen barrier, and determined the proportion of insects that flew over it. When released midway between a barrier and adjacent vegetation 71.5% of H. coagulata flew away from the barrier and in the direction of the vegetation; whereas 29.5% flew in the direction of the barrier. Of the total number of H. coagulata released, 7.5% flew over the barrier. When placed on the barrier, H. coagulata generally climbed up an average of 1.16 m before flying away from the structure. Of the total number of H. coagulata placed on the barrier, 6% flew over it. These results suggest that a screen barrier can be a part of a management strategy to reduce number of H. coagulata in high-value crops.

Influence of Seasonal Nitrogen Nutrition Fluctuations in Orange and Lemon Trees on Population Dynamics of the Glassy-Winged Sharpshooter (Homalodisca coagulata)

The glassy-winged sharpshooter (GWSS) is a xylem feeder that develops conspicuous, year-round populations in many citrus-producing regions of California. Field studies were conducted in a combined lemon and orange orchard to determine the influence of changing amino acid concentrations on relative densities of GWSS. Nineteen protein amino acids were detected in xylem fluid of both lemon and orange trees. Although annual profiles of total and essential amino acids were similar for each citrus species, mean concentrations were consistently higher in lemons than in oranges for most of the year, except for one critical period in late winter-early spring when concentrations were higher in oranges. Principal component analysis followed by factor analysis was performed individually on lemon and orange data sets to identify a reduced number of orthogonal factors composed of amino acids having similar seasonal profiles. Four factors were identified for each citrus species that accounted for 85% and 79% of the total variation in the orange and lemon analyses, respectively. These were then examined with respect to shifts in GWSS numbers that occurred asynchronously in lemons and oranges over the annual population cycle. Three distinctive number shifts were identified that included a peak in adult numbers in lemons during August 2001, significantly higher numbers in lemons relative to oranges during midwinter, and finally an increase in oranges of both adults and nymphs during spring 2002. Various groups of amino acids, i.e., factors, displayed peak annual or elevated levels during the intervals when shifts in GWSS numbers were occurring. Soluble protein levels in oranges and lemons did not correspond to shifting GWSS numbers as certain amino acids. However, soluble protein levels were higher in oranges during late winter/early spring when GWSS adults were sexually active. Potential roles of these amino acids and proteins in GWSS host selection are discussed.