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Polyphagous shot hole borer (PSHB), Euwallacea whitfordiodendrus (Schedl) (Coleoptera: Curculionidae, Scolytinae), is an ambrosia beetle that has recently invaded southern California, USA. This beetle successfully attacks and reproduces in a multitude of tree species. As direct control methods are limited, we investigated cultural management options, and sought to determine whether irrigation affects the number of attacks host trees experienced. If irrigation plays a role, cultural control methods could be recommended to managers and growers. Three separate experiments were conducted that monitored the number of attacks on trees with different levels of irrigation. Two experiments examined PSHB attacks in established landscape trees where irrigation was either present or absent. A third experiment used young potted box elder with irrigation controlled with timed emitters. In all three experiments, the level of irrigation received by the trees did not affect the number of attacks. The results suggest that changes in irrigation practices do not affect risk from PSHB attack.

Polyphagous shot hole borer (PSHB) (Euwallacea spec.; Coleoptera: Curculionidae: Scolytinae) has recently invaded southern California, USA. Along with its associated fungi, the beetle causes branch dieback and tree mortality in more than 200 host tree species, including avocado (Persea americana Mill., Lauraceae) and many important native, urban landscape, and nursery stock trees. As PSHB spreads into the avocado-growing regions of southern California, there is a pressing need for more information for effective management of the insect/fungus complex. The objective of this study was to examine avocado cultivars to see whether there were differences in susceptibility to attack and gallery development from PSHB. We conducted choice and no-choice trials with cut branches in the laboratory, artificially infested avocado saplings with PSHB, and also surveyed attack rates for two cultivars of field-grown avocado subject to natural attack by PSHB. Laboratory and field trials showed similar patterns for preference among avocado cultivars indicated by beetle attack rates and gallery formation. Among the common commercial cultivars, Fuerte, Gwen, and Bacon most often had lower attack rates and lower rates of gallery formation. Zutano most frequently indicated high attack rates and much gallery formation, indicating that it may be the most susceptible to PHSB of the commercial cultivars.

Polyphagous shot hole borer (PSHB) has recently invaded southern California. This beetle attacks more than 200 host tree species, including avocado (Persea americana Mill.) and many important native, urban landscape and nursery stock trees including sycamore (Platanus racemosa Nutt.), and box elder (Acer negundo L.). The beetle, along with its associated fungi, causes branch dieback and tree mortality in a large variety of tree species. Due to the severity of the impact of PSHB, short-term management tools must include chemical control options for the industry and private landowners to protect trees. We assessed the effectiveness of systemic and contact insecticides for control of PSHB in laboratory tests using fresh-cut castor bean (Ricinus communis L.) branches. Castor bean was chosen because, as a weedy species, it is widely available, and it is a preferred host for the beetles. We conducted field tests using mature, weedy, infested field-grown castor bean. We also surveyed infested coral trees (Erythrina corallodendron L.) in an established residential landscape. For field-grown infested castor bean, beetle activity was lowest for plants treated with bifenthrin, imidacloprid and dinotefuran. Bifenthrin was the most effective insecticide for reducing beetle attacks and gallery formation in castor bean branches in laboratory experiments with cut branches. Dinotefuran was more variable in effectiveness in laboratory trials. Fenpropathrin, clothianidin and orange oil extracts did not differ from untreated controls in beetle attacks and gallery formation. Based on these results, bifenthrin and imidacloprid were selected for further testing in combination with fungicides for control of PSHB.

A recently discovered ambrosia beetle with the proposed common name of polyphagous shot hole borer (Euwallacea sp., Coleoptera: Curculionidae: Scolytinae), is reported to attack >200 host tree species in southern California, including many important native and urban landscape trees. This invasive beetle, along with its associated fungi, causes branch dieback and tree mortality in a large variety of tree species including sycamore (Platanus racemosa Nutt.). Due to the severity of the impact of this Euwallacea sp., short-term management tools must include chemical control options for the arboriculture industry and private landowners to protect trees. We examined the effectiveness of insecticides, fungicides, and insecticide-fungicide combinations for controlling continued Euwallacea sp. attacks on previously infested sycamore trees which were monitored for 6 mo after treatment. Pesticide combinations were generally more effective than single pesticide treatments. The combination of a systemic insecticide (emamectin benzoate), a contact insecticide (bifenthrin), and a fungicide (metconazole) provided some level of control when applied on moderate and heavily infested trees. The biological fungicide Bacillus subtilis provided short-term control. There was no difference in the performance of the three triazole fungicides (propiconazole, tebuconazole, and metconazole) included in this study. Although no pesticide combination provided substantial control over time, pesticide treatments may be more effective when trees are treated during early stages of attack by this ambrosia beetle.

The precision and accuracy of the determination of particu-late sulfate and fluoride, and gas phase SO2 and HF are estimated from the results obtained from collocated replicate samples and from collocated comparison samples for high-and low-volume filter pack and annular diffusion denuder samplers. The results of replicate analysis of collocated samples and replicate analyses of a given sample for the determination of spherical aluminosilicate fly ash particles have also been compared. Each of these species is being used in the chemical mass balance source apportionment of sulfur oxides in the Grand Canyon region as part of Project MOHAVE, and the precision and accuracy analyses given in this paper provide input to that analysis. The precision of the various measurements reported here is ±1.8 nmol/m3 and ±2.5 nmol/m3 for the determination of SO2 and sulfate, respectively, with an annular denuder. The precision is ±0.5 nmol/m3 and ±2.0 nmol/m3 for the determination of the same species with a high-volume or...

Honeydew-producing psyllids are an important pest of eucalyptus (Myrtaceae) in California, USA, and may influence surrounding litter arthropod communities. In particular, the introduced Australian psyllids Glycaspis brimblecombei Moore and Eucalyptolyma maideni Froggatt (both Hemiptera: Psyllidae) may facilitate the prevalence of invasive ant species. We examined ground-dwelling arthropod communities under eucalyptus trees infested by psyllids. We used a model comparison approach to examine the association of psyllid infestation, ant abundance, and environmental factors with ground arthropod abundance and richness. We found a significant positive association between ant activity on eucalyptus trees and psyllid abundance. Higher psyllid abundance and higher Argentine ant abundance were associated with increased arthropod richness. Irrigation was also associated with increased arthropod richness and abundance. Regardless of location collected, arthropod communities collected in pitfall traps under trees with high psyllid abundance had high similarity to arthropod communities under trees with high ant activity. Abundance of isopods was positively associated with both ant and psyllid abundance. Other arthropod groups differed in their association with ants and psyllids. Argentine ants may exacerbate pest impacts and may also decrease the effectiveness of biological control programs for eucalyptus lerp psyllids.

Although it has been speculated that ant visits to extrafloral nectaries of bracken fern may convey a fitness benefit for the plant, this has never been demonstrated with native herbivores and natural insect densities. We tested the hypothesis that ants attracted to extrafloral nectaries of bracken fern provide a mutualistic benefit by protecting fronds from herbivore damage in a field manipulation experiment in southern California. We examined densities of sawfly eggs and larvae on bracken fronds with and without ant exclusion. Because bracken fern in this region is also impacted by nitrogenous air pollution, we included an N addition treatment. We found that sawfly egg abundance was significantly higher for fern plants when ants were excluded, regardless of N treatment. Ants tended to have higher abundance on fertilized plants, but there was no interaction between N additions and ant exclusion. Bracken fern may derive a fitness benefit from attracting ants during the early phases of plant growth, through decreased herbivore oviposition, rather than through the deterrence of feeding larvae.

To evaluate plant and herbivore responses to nitrogen we conducted a fertilization study at a low and high pollution site in the mixed conifer forests surrounding Los Angeles, California. Contrary to expectations, discriminant function analysis of oak herbivore communities showed significant response to N fertilization when atmospheric deposition was high, but not when atmospheric deposition was low. We hypothesize that longer-term fertilization treatments are needed at the low pollution site before foliar N nutrition increases sufficiently to affect herbivore communities. At the high pollution site, fertilization was also associated with increased catkin production and higher densities of a byturid beetle that feeds on the catkins of oak. Leaf nitrogen and nitrate were significantly higher at the high pollution site compared to the low pollution site. Foliar nitrate concentrations were positively correlated with abundance of sucking insects, leafrollers and plutellids in all three years of the study.

The forests surrounding the urban areas of the Los Angeles basin are impacted by ozone and nitrogen pollutants arising from urban areas. We examined changes in the herbivore communities of three prominent plant species (ponderosa pine, California black oak and bracken fern) at six sites along an air pollution gradient. Insects were extracted from foliage samples collected in spring, as foliage reached full expansion. Community differences were evaluated using total herbivore abundance, richness, Shannon-Weiner diversity, and discriminant function analysis. Even without conspicuous changes in total numbers, diversity or richness of herbivores, herbivore groups showed patterns of change that followed the air pollution gradient that were apparent through discriminant function analysis. For bracken fern and oak, chewing insects were more dominant at high pollution sites. Oak herbivore communities showed the strongest effect. These changes in herbivore communities may affect nutrient cycling in forest systems.

The precision and accuracy of the determination of particu-late sulfate and fluoride, and gas phase SO

Total fluoride (gas plus fine particle), spherical aluminosilicate particles, particulate selenium, arsenic, lead, bromine, and absorption of light by fine particles have been used to characterize chemical profiles for sources of sulfur oxides impacting the Grand Canyon National Park Class I Visibility Region. During the Project MOHAVE (Measurement of Haze and Visual Effects) winter and summer intensive studies in 1992, these various species were determined at seven sampling sites in and around the Grand Canyon. Extensive upper air and surface-based meteorological measurements were examined to determine probable geographical origins of the air mass present during a given sampling period for each sampling site. Samples corresponding to air masses dominated by transport from a single major source region were used to determine a source profile for each region. Source regions which have been characterized by this analysis include the San Joaquin Valley area, the southern California coastal urban area, the Baja, California-Imperial Valley area, the Arizona and Mexico area (including major smelters) south of the Grand Canyon, the area southeast of the Grand Canyon, the Colorado Plateau area, the Wasatch Front in Utah, and the area in Nevada to the west and northwest of the Grand Canyon. Source profiles giving the ratio of each endemic marker to SO x for each identified regional source in these areas have been determined. The source profiles for the various regional sources are all statistically different and distinguishable from those for other geographically adjoining sources.

During January-March of 1990 a study was conducted to determine the sources of sulfur oxides present at Canyonlands and Green River, Utah. Samples were collected at these two receptor sites and at several sites intended to characterize the chemical composition of air masses reaching the receptor sites from various geographical regions. The results of the sampling program have been given in the first paper in a series of three papers. In this paper, the concentrations of spherical aluminosilicate (SAS) particles, total fluoride, and particulate selenium, arsenic and lead are combined with meteorological data to obtain source fingerprints for the ratios of these species to SO x , from the various regional sources that can influence the Canyonlands sampling site. The results indicate that the variability in the ratios of these various species to SO x , from the various regional sources is large enough to provide useful input to a receptor based, chemical mass balance source apportionment of SO, at the receptor sites. The chemical mass balance analysis is given in the final paper of this series. The ratio of SAS: SO x , varies by a factor of 25 in emissions from various coal-fired power plants. The concentrations of lead and arsenic relative to sulfur oxides is also variable in emissions from different coal-fired power plants. The ratio of particulate selenium and total fluoride to SO x , in emissions from these coal-fired sources is relatively constant. Emissions from source regions containing smelters are high in Se, As and Pb. Emissions from source regions containing fluoride ore processing industries have a high F Tots; : SO x , ratio.

Spherical aluminosilicate (SAS) particles, total fluoride and particulate trace elements are potential endemic tracers for determining and quantifying the presence of coal-fired power plant and other sulfur oxide source emissions at far downwind distances. These endemic tracers, and sulfate and SO 2 were collected at Canyonlands National Park, at seven ambient sampling sites located in air mass transport paths to Canyonlands and from the stacks of coal-fired power plants in central Utah during January-March of 1990 for use in source apportionment analyses. These data have been combined with results obtained in concurrent studies by the National Park Service (EPIC study) and Salt River Project to provide a complete data set for the characterization of the regional and point sources that can influence air quality in the Canyonlands area. This paper gives details on the study design and on the chemical composition of fine particulate matter in the study area. While concentrations of SO x (SO 2 (g) plus particulate sulfate) were in good agreement among the various studies, accurate concentrations for sulfate and SO 2 were only obtained using a diffusion denuder sampling system because of the absorption of SO 2 (g) by particles in all filter pack sampling systems. Concentrations of FT Total (HF(g) plus particulate fluoride), and particulate Se, As, and Pb determined by multiple techniques were generally in good agreement. Sulfate (assumed present as ammonium sulfate) and nitrate (assumed present as ammonium nitrate) accounted for an average of 19 and 4%, respectively, of the fine particulate mass collected at Canyonlands and 8 and 2% of the fine particulate mass at Green River, Utah. Data were available at the Edge of the Cedars, Utah, sampling site to estimate the complete chemical composition of the fine particles. The average concentration of fine particles at Edge of the Cedars was 15 μg m −3 . Sulfate (as the ammonium salt) averaged 15% of the fine particulate mass, comparable to Canyonlands. Nonsulfate inorganic compounds averaged 58% of the mass. The majority of these inorganic species are background desert particles. The remainder of the mass, 27%, is presumably water, and organic and elemental carbon.

During January-March of 1990 a study was conducted to determine the sources of sulfur oxide emissions present in the Canyonlands area in Utah. Samples were collected at the Island-in-the-Sky visitors center in Canyonlands National Park and at several sites circling the park to characterize the chemical composition of air masses influencing the receptor sites from various geographical regions. The results of the sampling program and the identified chemical fingerprints of the sources that can impact the Canyonlands receptor site have been given in the first two papers in a series of three papers. In this paper are presented the results of chemical mass balance source apportionment of the SOx, present at Canyonlands, Green River, Bullfrog Marina and Edge of the Cedars, Utah, using the chemical composition and source fingerprint data given in the preceding papers. The results indicate that the presence of sulfur oxides at the Canyonlands area is a regional problem not dominated by a single source. The contributions to SOx, at Canyonlands during the 21 days included in the source apportionment analyses included sources to the southwest (37%),south and southeast (20%), north and northeast (19%), and northwest (23%). At the Edge of the Cedars State Park to the southeast of Canyonlands, sources from the southeast contributed 51 % of the observed SOx. At Bullfrog Marina in the Lake Powell National Recreation Area, southwest of Canyonlands, sources to the southwest were responsible for 81 % of the SOx present. At Green River, to the north of Canyonlands, the contribution of sources to the north and northeast were reduced (10%) because the major transport path of sources from these directions was the movement of emission from northwestern Colorado down the Colorado River drainage and south of Green River. The apportionment of sulfate at Canyonlands has been estimated from a combination of the chemical mass balance SOx source apportionment results, the measured concentrations of S02 and particulate sulfate, and meteorological data. This analysis indicates that, while the main source of SOx at Canyonlands is from emissions to the southwest, the main source of sulfate is from SOx emissions originating from the southeast of Canyonlands.

Particles collected in the desert Southwest on Teflon filters using an annular denuder sampling system absorb SO 2 (g) in a subsequential exposure to SO 2 (g) in the laboratory if the concentration of fine particulate sulfate measured with a filter pack sampling system is greater than the concentration of sulfate measured with the annular denuder sampling system. If the concentrations of sulfate determined using the two sampling systems agreed, no absorption of SO 2 (g) by the denuder-collected particles occurs. These results show that SO 2 (g) may be collected by Southwest desert fine particles during sampling, resulting in measured concentrations of fine particulate sulfate that are higher than the correct concentrations. The magnitude of this filter pack sampling artifact, 0.1-0.4 μg SO 4 2- /m 3 , is small. However, the artifact is important relative to the concentration of particulate sulfate present in the desert Southwest, typically 0.5-2 μg SO 4 2- /m 3 . The magnitude of the filter pack sulfate sampling artifact is not related to either the atmospheric particulate sulfate or SO 2 (g) concentrations.

The impact of atmospheric pollution, including nitrogen deposition, on bracken fern herbivores has never been studied. Bracken fern is globally distributed and has a high potential to accumulate nitrogen in plant tissue. We examined the response of bracken fern and its herbivores to N fertilization at a high and low pollution site in forests downwind of Los Angeles, California. Foliage from the high pollution site had higher total N and nitrate than the low pollution site. Bracken fern biomass, foliar N and herbivore abundance were all affected by fertilization treatments. Biomass and herbivore responses were greatest during a year of high precipitation. N additions at the low pollution site were primarily associated with decreased fern biomass, and with transient impacts on herbivore abundance. N additions significantly affected bracken fern and its herbivores at the high pollution site where foliar N and nitrate decreased in response to N addition treatments, while biomass and herbivore abundance increased. High atmospheric deposition and fertilization were both associated with increased herbivore richness. Herbivore abundance was most impacted by fertilization during the early expansion of fern fronds. The most abundant chewing herbivore, a sawfly, was positively associated with plant nitrogen at the low pollution site, but negatively associated with plant nitrogen at the high pollution site, where concentrations of both total N and nitrate were high. While overall growth and herbivore impacts in this xeric location were limited, the variable response we observed associated with rainfall, may indicate impacts could be larger in more mesic environments.

The free-living lemon gum psyllid, Cryptoneossa triangula Taylor, and the lerp-forming spotted gum psyllid, Eucalyptolyma maideni Froggatt (Hemiptera: Psyllidae) are invasive pests of eucalypts in California. In 2007, Psyllaephagus parvus Riek (Hymenoptera: Encyrtidae) was discovered parasitizing spotted gum psyllids and Psyllaephagus perplexans Cockerell was collected from lemon gum psyllids. While neither parasitoid species was purposely introduced, presence of the parasitoids was significantly associated with reduced intensity and duration of population peaks for both psyllid species. Spring peaks were reduced more than fall peaks. We estimated minimum rates of parasitism from the ratio of mummies to live nymphs. Higher parasitism was recorded in coastal than inland locations during the spring, while parasitism was similar for coastal and inland populations in the fall. Logistic regression models suggest parasitoids were the determining factor of psyllid population densities, although physical parameters, such as irrigation, may affect psyllid or parasitoid populations.