Glassy-Winged Sharpshooter's (GWSS) Population Dynamics as a Means of Gaining Insight Into the Management of GWSS … (original) (raw)
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IDENTIFYING KEY PREDATORS OF THE GLASSY-WINGED SHARPSHOOTER IN A CITRUS ORCHARD Project Leaders
2000
Over 1,500 predators were screened for glassy-winged sharpshooter (GWSS) remains using a GWSS egg-specific monoclonal antibody (MAb) and several GWSS-specific genetic markers. Specimens were collected in 2002 and 2003 from a citrus orchard (Riverside, CA) harboring high densities of GWSS. We found that 6.2% of all specimens examined tested positive for GWSS remains. The most frequent predators to test positive
GLASSY-WINGED SHARPSHOOTER IMPACT ON ORANGE YIELD, FRUIT SIZE, AND QUALITY Project Leader
2000
The California citrus growers needed to know what impact if any the glassy-winged sharpshooter Homalodisca coagulata (GWSS) has on fruit yield, size and quality as well as tree vigor. The goals of this project are to determine the usefulness of the management of GWSS to prevent yield loss, fruit size reduction, and degraded fruit quality. First we have to know what impact GWSS has on citrus, and second we need to know how to use currently available materials against the GWSS in IPM programs to prevent potential losses as well as minimizing negative impact to other citrus pests. This information is paramount before we can even begin to incorporate these into conventional IPM programs. Prior to the initiation of this study, we didn't know what the effects of heavy GWSS feeding has on the vigor of citrus trees or fruit yield, size, sugar/acid ratio, peel thickness etc. GWSS suppression in citrus was done to prevent the movement of GWSS into grape under areawide management programs to limit the spread of Xylella fastidiosa (Xf). Therefore, the focus of this study is to determine the impact of heavy GWSS feeding on citrus yields, fruit size, and quality.
Prior to this study, it was unknown what impact the glassy-winged sharpshooter (GWSS), Homalodisca coagulata, had on fruit yield, fruit size, and quality as well as tree vigor. The effects of the high feeding populations of GWSS on navel orange peel nutrient status and metabolism have been consistent for the four years of the study. High GWSS feeding populations significantly reduced peel Ca and Mg concentrations all years of the study: year 1 (P≤0.05) and year 2 compared to the low GWSS population (P≤0.001). High GWSS feeding populations significantly disrupted N metabolism causing high peel nitrate-N or total N in years 1 and 2, respectively (P≤0.05). High GWSS feeding populations significantly increased peel arginine and putrescine concentrations in four years of the study with the magnitude of the difference between the two treatments greater in years 2 and 3 (P≤0.05). High GWSS feeding populations resulted in a numerically higher concentration of proline in year 1 and a significantly higher proline concentration in year 2 (P≤0.05). Although GWSS feeding causes changes in peel Ca, Mg and N status, high levels of feeding and the induced changes occur after maximum peel thickness and, thus far, have not affected external fruit quality. The changes in metabolism induced by GWSS feeding are indicative of tree stress. The increased magnitude and statistical significance of these metabolic changes over the first two years of high GWSS feeding pressure is consistent with cumulative stress to the trees. High feeding pressure resulted in significant yield losses in 'Washington' navel oranges.
2006
Outlined experiments in this study have only recently begun and are designed to advance our ability to define the operative host-plant factors utilized by adult glassy-winged sharpshooter (GWSS) and associated natural enemies as long-range cues to locate feeding and oviposition hosts in a complex agricultural landscape. Specifically, experiments are underway to determine how continuous deficit irrigation regimes in Valencia oranges influence the population dynamics of GWSS and other associated natural enemies. Populations of GWSS were monitored in a citrus orchard maintained under continuous irrigation schedules receiving 60%, 80%, and 100% of evapo-transpiration (ET c ) rates. Throughout the season, citrus trees irrigated at 60% ET c had warmer leaves and higher water potential than the trees irrigated with 80% and 100% ET c . Mean numbers of adults collected on beat samples, caught on sticky traps, and observed during the visual inspection, and egg masses within foliage were higher in the 80% and 100% ET c treatments than the 60% ET c treatment. Preliminary caged experiments using grape and oleander conducted in Riverside, California, illustrated GWSS population shifts that occurred between plants. Individual plants maintained under a well-watered treatment (ET c =100%) exhibited higher insect counts compared with a continuous deficit-irrigated treatment (ET c =50%). Identifying how the dispersing lifestages of GWSS locate and exploit specific host species will begin to provide the necessary information required to develop strategies for control of this highly mobile insect and further to limit the spread of Xf movement into susceptible crops.
Glassy Winged Sharpshooters in Avocado Orchards in Southern California
2000
After increased populations of Homalodisca coagulata (GWSS) in avocado orchards were reported by growers in both San Diego and Ventura Counties in 2001, this study was initiated. In 2002, two sites in each county were selected to document the occurrence of GWSS in an avocado grove adjacent to an orange grove and to evaluate the possible threat of GWSS to
A combination of field and laboratory experiments in this study have been designed to advance our understanding of the operative host-plant factors utilized by adult glassy-winged sharpshooters (GWSS) and associated natural enemies as long- range cues to locate feeding and oviposition hosts in a complex agricultural landscape. Specifically, a second year of field studies have been conducted to determine the influence of continuous deficit irrigation regimes implemented in sweet orange cv. 'Valencia' oranges on the population dynamics of GWSS and other associated natural enemies. Dispersal and population dynamics of GWSS were monitored under continuous irrigation treatments receiving 60%, 80%, and 100% of evapo- transpiration (ETc) rates. Similar to the results obtained in our 2005 season, citrus trees irrigated at 60% ETc had warmer leaves, significantly higher xylem matric potential, and fewer adult and immature GWSS than experimental trees irrigated with 80% and 100% ETc. ...
Journal of Economic Entomology, 2009
A 2-yr study was conducted in a citrus orchard (Citrus sinensis L. Osbeck cultivar Valencia) to determine the inßuence of plant water stress on the population dynamics of glassy-winged sharpshooter, Homalodisca vitripennis (Germar). Experimental treatments included irrigation at 100% of the crop evapotranspiration rate (ET c ) and continuous deÞcit-irrigation regimens at 80 and 60% ET c . Microclimate and plant conditions monitored included temperature and humidity in the tree canopy, leaf surface temperature, water potential, and fruit quality and yield. Glassy-winged sharpshooter population densities and activity were monitored weekly by a combination of visual inspections, beat net sampling, and trapping. Glassy-winged sharpshooter populations were negatively affected by severe plant water stress; however, population densities were not linearly related to decreasing water availability in plants. Citrus trees irrigated at 60% ET c had signiÞcantly warmer leaves, lower xylem water potential, and consequently hosted fewer glassy-winged sharpshooter eggs, nymphs, and adults than trees irrigated at 80% ET c . Citrus trees irrigated at 100% ET c hosted similar numbers of glassy-winged sharpshooter stages as trees irrigated at 60% ET c and a lower number of glassy-winged sharpshooter nymphs than the 80% ET c treatment, speciÞcally during the nymphal density peak in mid-April to early July. Irrigation treatments did not affect populations of monitored natural enemies. Although the adult glassy-winged sharpshooter population was reduced, on average, by 50% in trees under severe water stress, the total number of fruit and number of fruit across several fruit grade categories were signiÞcantly lower in the 60% ET c than in the 80 and 100% ET c irrigation treatments.
Population trend and fruit damage of Pezothrips kellyanus in citrus orchards in Valencia (Spain)
Damage produced by thrips (Thysanoptera) has been traditionally considered rare or absent in Spanish citrus orchards. However, Pezothrips kellyanus (Bagnall) was first observed in Alzira (Valencia province) in 2007 damaging citrus fruits. Since then, the pest has extended to other citrus areas in eastern Spain causing important damage. Worldwide, P. kellyanus has emerged during the last decade as a pest of citrus fruits. Its presence and fruit-scarring damage in citrus orchards has been recorded since the 1990s in Australia, New Zealand and some Mediterranean countries. Nowadays, some basic aspects of its biology, which are necessary for the adequate management of the pest, still remain poorly understood. In order to study the relationship between the seasonal trend of its different development stages and fruit damage, P. kellyanus populations were monitored in several citrus orchards using different sampling methods (aerial and ground sticky traps, Berlese funnels and visual inspection), during 2008 and 2009. Seasonal trends in relative abundances of different development stages were studied in oranges, lemons and jasmines. Our results show that fruit damage is strongly correlated with number of larvae on young fruits and poorly correlated with number of adults on flowers or young fruits. The utility of different sampling methods to estimate the number of generations and to predict the damage to fruits is discussed. Several species of soil dwelling predatory mites were identified in the soil around thrips-infested citrus and jasmine.
Biocontrol, 2002
Seasonal mortality of the citrusleafminer, Phyllocnistis citrellaStainton, was studied from 1994 through 1998 in`Tahiti' lime, Citrus aurantifolia (Christm.) Swingle,in Homestead, Florida. Survival of eachdevelopmental host stage and the proportionattacked by indigenous and introduced naturalenemies were determined. Before the recovery ofthe introduced parasitoid, Ageniaspiscitricola Logvinovskaya, in 1995, thethird-instar host had the highest averageproportion of parasitized individuals (0.14)followed by the prepupa (0.11) while the firstinstar had the lowest proportion parasitized(0.02). After the first recovery andestablishment of A. citricola, theproportion of pupae parasitized increased to0.56 followed by the prepupa (0.14) and thethird instar (0.11). Before the introduction ofA. citricola, the highest proportion ofhosts killed by predation was observed insecond instar (0.17) and third instar (0.15).After the establishment of the introducedspecies, the proportion of dead individuals dueto predation was greater for second instar(0.31) and third instar (0.21) larvae.Mortality caused by indigenous natural enemieswas significantly correlated with increases ofP. citrella density. Parasitism ofP. citrella by the exotic parasitoid,A. citricola, correlated less well to hostdensity over the season (r2 = 0.12) thandid mortality caused by indigenous naturalenemies (r2 = 0.76). Moreover, a higherpercent mortality in population of P. citrellawas obtained from predation by theindigenous natural enemies than the introducedparasitoid as shown in the mortality estimatesfrom 1995 to 1998.