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.

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Polyphagous shot hole borer (Euwallacea sp., Coleoptera: Curculionidae: Scolytinae) has recently invaded southern California. The beetle, along with its associated fungi, Fusarium euwallaceae, Graphium sp., and Acremonium sp., causes branch dieback and tree mortality in a large variety of tree species including avocado (Persea americana Mill.) and box elder (Acer negundo L.). With the spread of the beetle through Los Angeles, Orange, and San Diego Counties in California, there is increasing concern that felled trees and pruned branches infested with polyphagous shot hole borer should receive sanitation treatment to reduce the potential spread of the beetle from the movement of untreated wood. We tested two sanitation methods to reduce beetle populations, chipping with a commercial chipper and solarization by covering logs with clear or black plastic in full sun. Both chipping and solarization decreased beetle emergence and boring activity compared to untreated control logs. Chipping was most effective for chip sizes <5 cm. Solarization was most effective using clear polyethylene sheeting during hot summer months, particularly August, when daily maximum temperatures were ≥35°C. Beetles persisted for 2 mo or more when solarization was applied during the spring or fall.

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.

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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.

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