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Abstract: A study was conducted to determine the lethal effects of systemic imidacloprid against the egg stage of the glassy-winged sharpshooter Homalodisca vitripennis, and its mymarid egg parasitoid Gonatocerus ashmeadi. During the development of the sharpshooter embryo within the egg, imidacloprid did not have a lethal effect, even at very high concentrations. However, upon emergence from the egg mass, the 1st instar nymph encountered residues of imidacloprid in the surrounding leaf tissues. When mortality was assessed within 48h of emergence, there was an excellent dose–response between the imidacloprid concentration and nymph mortality, giving an LC50 of 39ngimidacloprid per cm2 leaf. In the same way, G. ashmeadi did not succumb to lethal levels of imidacloprid during its development within the sharpshooter egg. However, parasitoid adults were sensitive to imidacloprid residues during emergence from the sharpshooter egg. When mortality was assessed within 48h of emergence, the LC50 for the parasitoid was 66ngimidacloprid per cm2 leaf. In a survey of commercial citrus trees that were treated with imidacloprid, the mean residues of the insecticide within the leaves did not exceed the LC50 concentrations for either insect. The implications of these results for the integration of biological and chemical controls are discussed. [Copyright &y& Elsevier]

Abstract: Gonatocerus ashmeadi is an important egg parasitoid of the glassy-winged sharpshooter, Homalodisca coagulata, in California. Although adults of this parasitoid are easily identified from morphological characteristics, their identification as immatures within eggs is more difficult, particularly during the early stages of development. In this study, we show that esterase profiles determined by polyacrylamide gel electrophoresis (PAGE) can be used to detect this species in parasitized eggs within two days of parasitization. The expression of esterase E0.17 occurred at a time when mymarid parasitoids would be expected to hatch within the host egg. The intensity of this band increased as the parasitoid developed within the sharpshooter egg. After five days, a second parasitoid esterase, E0.13, was detected. These two esterases were clearly distinct from all sharpshooter esterases. The electrophoretic technique was also sensitive enough to detect a polymorphic esterase locus in adult insects originating from San Juan Capistrano in California. [Copyright &y& Elsevier]

Synthetic pyrethroids and neonicotinoids are the most readily available alternatives to the organophosphate and carbamate insecticides. Pyrethroids have become widely used in California, and problems with insecticide resistance and nontarget impacts have already been identified. Neonicotinoids are a new class of insecticide with uses only now being realized. Managing insecticide resistance will be crucial to preserving these new materials as organophosphate uses are lost. [ABSTRACT FROM AUTHOR]

The greenhouse whitefly, Trialeurodes vaporariorum (Westwood), is an important pest of strawberries in California, USA. The adults and nymphs feed on phloem sap of leaves to remove the photo-assimilates. The objective of this study is to test the impact of whitefly management with insecticides on strawberry fruit quality. Applications of imidacloprid, thiamethoxam, buprofezin and pyriproxyfen decreased the mean adult white-fly numbers by 2.80-, 2.17-, 1.69- and 1.39-fold, respectively, compared to the untreated control. Similarly, the mean numbers of first and second instar whiteflies were reduced 4.36-, 2.20-, 1.90- and 2.02-fold, respectively, while the mean numbers of third and fourth instars were reduced 5.48-, 2.28-, 2.71- and 1.43-fold, respectively, in plants treated with imidacloprid, thiamethoxam, buprofezin and pyriproxyfen. The mean soluble solids content in imidacloprid, thiamethoxam, buprofezin and pyriproxyfen treatments was 1.04-, 1.06-, 1.03- and 1.04-fold greater, respectively, than that in the control. The whitefly reduction enhanced the mean fruit titratable acidity by 4%-6%. Mean glucose levels in imidacloprid and thiamethoxam treatments were significantly higher than in other treatments. However, the whitefly management did not affect the mean fructose levels. Imidacloprid, thiamethoxam and pyriproxyfen treatments boosted the ascorbic acid levels by up to 4%. The impact of whitefly management on strawberry fruit nutrition and antioxidant capacity is discussed. [ABSTRACT FROM AUTHOR]

The impacts of planting date and nitrogen fertilization on cotton ( Gossypium hirsutum L.) photosynthesis and soluble carbohydrate contents in relation to silverleaf whitefly, Bemisia tabaci (Gennadius) biotype “B”, populations were examined in field experiments. Cotton planted in late April and early June was treated with 0,112, 168 and 224 kg/N hectare in soil using urea fertilizer. The mean photosynthetic rate of April-planted cotton was 4%J20% higher than that of June-planted cotton early in the season, but 10%J 18% lower than that of June-planted cotton late in the season. The photosynthetic rates for both planting dates were positively correlated with levels of added nitrogen. While levels of glucose for both planting dates were positively correlated with nitrogen levels, fructose and sucrose levels were not. The mean levels of fructose were up to 40% lower, while that of sucrose were up to 59% higher, in April-planted cotton than in June-planted cotton. Levels of photosynthetic rate or stomatal conductance were not correlated with adult whitefly densities for either planting date. Levels of glucose and fructose were positively correlated with whitefly densities only for June-planted cotton late in the season. [ABSTRACT FROM AUTHOR]

The carmine spider mite, Tetranychus cinnabarinus (Boisduval) and the twospotted spider mite, Tetranychus urticae Koch, are serious pests of strawberries and many other horticultural crops. Control of these pests has been heavily dependent upon chemical acaricides. Objectives of this study were to determine the resistance status of these two pest species to commonly used acaricides on strawberries in a year-round intensive horticultural production region. LC90 of abamectin for adult carmine spider mites was 4% whereas that for adult twospotted spider mites was 24% of the top label rate. LC90s of spiromesifen, etoxazole, hexythiazox and bifenazate were 0.5%, 0.5%, 1.4% and 83% of their respective highest label rates for carmine spider mite eggs, 0.7%, 2.7%, 12.1% and 347% of their respective highest label rates for the nymphs. LC90s of spiromesifen, etoxazole, hexythiazox and bifenazate were 4.6%, 11.1%, 310% and 62% of their respective highest label rates for twospotted spider mite eggs, 3%, 13%, 432,214% and 15% of their respective highest label rates for the nymphs. Our results suggest that T. cinnabarinus have developed resistance to bifenazate and that the T. urticae have developed resistance to hexythiazox. These results strongly emphasize the need to develop resistance management strategies in the region. [ABSTRACT FROM AUTHOR]

Xylella fastidiosa causes a serious Pierce's disease (PD) in grapevine. Xylella fastidiosa cells from a PD strain were grown in a pure xylem fluid of a susceptible grapevine cultivar vs. xylem fluid from citrus, which is not a host for this strain of X. fastidiosa. When grown in grapevine xylem fluid, cells of the PD strain formed clumps and biofilm formed to a greater extent than in citrus xylem fluid, although the PD strain did grow in xylem fluid of three citrus varieties. The differential expression of selected genes of a PD X. fastidiosa strain cultured in the two xylem fluids was analyzed using a DNA macroarray. Compared with citrus xylem fluid, grapevine xylem fluid stimulated the expression of X. fastidiosa genes involved in virulence regulation, such as gacA, algU, xrvA, and hsq, and also genes involved in the biogenesis of pili and twitching motility, such as fimT, pilI, pilU, and pilY1. Increased gene expression likely contributes to PD expression in grapevine, whereas citrus xylem fluid did not support or possibly suppressed the expression of these virulence genes. [ABSTRACT FROM AUTHOR]