Copyright (c) 2009 University of Nebraska - Lincoln All rights reserved. http://digitalcommons.unl.edu/usdaarsfacpub Recent documents in Publications from USDA-ARS / UNL Faculty en-us Thu, 29 Oct 2009 23:21:15 PDT 3600 http://digitalcommons.unl.edu/usdaarsfacpub/396 http://digitalcommons.unl.edu/usdaarsfacpub/396 Wed, 28 Oct 2009 11:13:48 PDT Catnip (Nepeta cataria) is known for its pseudo-narcotic effects on cats. Recently, it has been reported as an effective mosquito repellent against several Aedes and Culex species, both topically and spatially. Our laboratory bioassays showed that catnip essential oil (at a dosage of 20 mg) resulted in average repellency rates of 96% against stable flies, Stomoxys calcitrans (L.) and 79% against houseflies, Musca domestica (L.), respectively. This finding suggested that the application of repellent could be used as part of filth fly management. Further evaluations of catnip oil toxicity were conducted to provide a broad-spectrum safety profile of catnip oil use as a potential biting and nuisance insect repellent in urban settings. Acute oral, dermal, inhalation, primary dermal and eye irritation toxicity tests were performed. The acute oral LD50 of catnip oil was found to be 3160 mg/kg body weight (BW) and 2710 mg/kg BW in female and male rats, respectively. The acute dermal LD50 was > 5000 mg/kg BW. The acute inhalation LD50 was observed to be > 10 000 mg/m3. Primary skin irritation tested on New Zealand white rabbits showed that catnip oil is a moderate irritant. Catnip oil was classified as practically non-irritating to the eye. In comparison with other U.S. Environmental Protection Agency-approved mosquito repellents (DEET, picaridin and p-menthane-3,8-diol), catnip oil can be considered as a relatively safe repellent, which may cause minor skin irritation. J. J. Zhu http://digitalcommons.unl.edu/usdaarsfacpub/395 http://digitalcommons.unl.edu/usdaarsfacpub/395 Wed, 28 Oct 2009 11:06:21 PDT Auto-fluorescent mapping of plant cell walls was used to visualize cellulose and lignin in pristine switchgrass (Panicum virgatum) stems to determine the mechanisms of biomass dissolution during ionic liquid pretreatment. The addition of ground switchgrass to the ionic liquid 1-n-ethyl-3-methylimidazolium acetate resulted in the disruption and solubilization of the plant cell wall at mild temperatures. Swelling of the plant cell wall, attributed to disruption of inter- and intramolecular hydrogen bonding between cellulose fibrils and lignin, followed by complete dissolution of biomass, was observed without using imaging techniques that require staining, embedding, and processing of biomass. Subsequent cellulose regeneration via the addition of an anti-solvent, such as water, was observed in situ and provided direct evidence of significant rejection of lignin from the recovered polysaccharides. This observation was confirmed by chemical analysis of the regenerated cellulose. In comparison to untreated biomass, ionic liquid pretreated biomass produces cellulose that is efficiently hydrolyzed with commercial cellulase cocktail with high sugar yields over a relatively short time interval. Seema Singh http://digitalcommons.unl.edu/usdaarsfacpub/394 http://digitalcommons.unl.edu/usdaarsfacpub/394 Wed, 28 Oct 2009 11:02:26 PDT Switchgrass (Panicum virgatum L.) is being developed into a perennial, herbaceous, cellulosic feedstock crop for use in temperate regions of the USA. Information on spatial and temporal variation for stands and biomass yield among and within fields in large agroecoregions is not available. Spatial and temporal variation information is needed to model feedstock availability for biorefineries. In this 5-yr study, the spatial and temporal variation for biomass yield and stands was determined among and within 10 fields located in North Dakota, South Dakota, and Nebraska. Switchgrass fields were managed for bioenergy from 2000 to 2004 for the Nebraska locations and 2001 to 2005 for the South Dakota and North Dakota locations. A global positioning system (GPS) receiver was used to repeatedly measure within field quadrat sites for switchgrass stands using frequency grid (2.25 m2) measurements in June for five growing seasons. Sixteen quadrat (≥1 m2) yield samples were taken post-killing frost in the establishment year and in August in subsequent years at each location. Topographic within field effects on switchgrass stand frequency and biomass yields were largely insignificant. Stands tended to increase from establishment year to year 3 and then begin to plateau. Weather factors, which were the principal source of temporal variation, were more important in switchgrass yield variation than on switchgrass stand frequencies. Temporal standard deviations for yield were higher on quadrat sites with higher than average field means while temporal standard deviations were smaller in quadrat sites that had lower than average field means at six locations. In the Northern Great Plains agroecoregion, there is greater temporal and spatial variation for switchgrass biomass yields among fields than within fields. Results indicate that modeling feedstock availability for a biorefinery can be based on field scale yields. M. R. Schmer http://digitalcommons.unl.edu/usdaarsfacpub/393 http://digitalcommons.unl.edu/usdaarsfacpub/393 Wed, 28 Oct 2009 10:38:06 PDT Recent advances in optical designs and electronic circuits have allowed the transition from passive to active proximal sensors. Instead of relying on the reflectance of natural sunlight, the active sensors measure the reflectance of modulated light from the crop and so they can operate under all lighting conditions. This study compared the potential of active and passive canopy sensors for predicting biomass production in 25-32 randomly selected positions of a Merlot vineyard. Both sensors provided estimates of the normalized difference vegetation index (NDVI) from a nadir view of the canopy at veraison that were good predictors of pruning weight. Although the red NDVI of the passive sensors explained more of the variation in biomass (R2 = 0.82), its relationship to pruning weight was nonlinear and was best described by a quadratic regression (NDVI = 0.55 + 0.50 wt-0.21 wt2). The theoretically greater linearity of the amber NDVI-biomass relationship could not be verified under conditions of high biomass. The linear correlation to stable isotope content in leaves (<sup13C and 15N) provided evidence that canopy reflectance detected plant stresses as a result of water shortage and limited fertilizer N uptake. Thus, the canopy reflectance data provided by these mobile sensors can be used to improve site-specific management practices of vineyards. Stamatis Stamatiadis http://digitalcommons.unl.edu/usdaarsfacpub/392 http://digitalcommons.unl.edu/usdaarsfacpub/392 Wed, 28 Oct 2009 10:31:20 PDT Smooth brome (Bromus inermis Leyss.) is an aggressive invader of fescue prairie; however, little information is available on the germination ecology of this exotic perennial relative to native flora. This information is needed to understand the processes of invasion and to develop strategies to curb the spread of smooth brome. Germination of smooth brome and plains rough fescue (Festuca altaica subsp. hallii (Vasey) Harms) seeds was compared under various temperature regimes, levels of water stress, and light. Germination of both species was severely restricted by water stress, but not by temperatures between 5 and 25°C. Smooth brome had higher germination over a broader range of temperatures and water stress than plains rough fescue. When incubation temperatures were decreased from 25 to 5°C, total germination was reduced for plains rough fescue relative to temperatures that were increased from 5 to 25°C; germination of smooth brome was similar under increasing or decreasing temperatures. At a given level of water stress at 10 and 20°C, plains rough fescue germination was unaffected by light and darkness. Germination was higher for smooth brome in dark than in light at 10°C, but at 20°C it was generally similar in light and darkness. Germination of smooth brome over a wide range of temperatures, light, and moisture conditions increases the probability that requirements will be met in heterogeneous seedbed conditions. Smooth brome is well adapted to germinate and establish in prairie dominated by plains rough fescue. Perry L. Grilz http://digitalcommons.unl.edu/usdaarsfacpub/391 http://digitalcommons.unl.edu/usdaarsfacpub/391 Wed, 28 Oct 2009 10:20:06 PDT Bioassays of six racemic synthesized candidate sex pheromone compounds against male New World screwworm Cochliomyia hominivorax (Coquerel) flies showed that the most potent bioactivity was found with 6-acetoxy-19-methylnonacosane and 7-acetoxy-15-methylnonacosane compared with four other isomeric acetoxy nonacosanes and a larger aliphatic ketone. As all these methyl-branched compounds have two asymmetric carbons and four possible enantiomers, characterization of the natural enantiomers was essential. All four enantiomers for the two most bioactive isomers of the natural sex pheromone were synthesized for bioassay. Hydrolysis and derivatization of these enantiomers with different fluorescent reagents was followed by columnswitched high-performance liquid chromatography. The use of two linked, reversed-phase columns of different polarity held at sub-ambient temperatures allowed good separation of each enantiomer. This analysis applied to natural material was successful, as (6R, 19R )-6-acetoxy-19-methylnonanocosane, and (7R, 15R )- and (7R, 15S)-7-acetoxy-15-methylnonanocosane were detected in extracts of recently colonized female flies. K. Akasaka http://digitalcommons.unl.edu/usdaarsfacpub/390 http://digitalcommons.unl.edu/usdaarsfacpub/390 Tue, 13 Oct 2009 13:43:40 PDT Using uniplex RT-PCR we screened honey bee colonies for the presence of several bee viruses, including black queen cell virus (BQCV), deformed wing virus (DWV), Kashmir bee virus (KBV), and sacbrood virus (SBV), and described the detection of mixed virus infections in bees from these colonies. We report for the first time that individual bees can harbor four viruses simultaneously. We also developed a multiplex RT-PCR assay for the simultaneous detection of multiple bee viruses. The feasibility and specificity of the multiplex RT-PCR assay suggests that this assay is an effective tool for simultaneous examination of mixed virus infections in bee colonies and would be useful for the diagnosis and surveillance of honey bee viral diseases in the field and laboratory. Phylogenetic analysis of putative helicase and RNA-dependent RNA polymerase (RdRp) encoded by viruses reveal that DWV and SBV fall into a same clade, whereas KBV and BQCV belong to a distinct lineage with other picorna-like viruses that infect plants, insects and vertebrates. Results from field surveys of these viruses indicate that mixed infections of BQCV, DWV, KBV, and SBV in the honey bee probably arise due to broad geographic distribution of viruses. Yanping Chen http://digitalcommons.unl.edu/usdaarsfacpub/389 http://digitalcommons.unl.edu/usdaarsfacpub/389 Tue, 13 Oct 2009 13:37:36 PDT Transient expression of engineered reporter RNAs encoding an intron-containing green fluorescent protein (GFP) from a Potato virus X-based expression vector previously demonstrated the nuclear targeting capability of the 359 nucleotide Potato spindle tuber viroid (PSTVd) RNA genome. To further delimit the putative nuclear-targeting signal, PSTVd subgenomic fragments were embedded within the intron, and recombinant reporter RNAs were inoculated onto Nicotiana benthamiana plants. Appearance of green fluorescence in leaf tissue inoculated with PSTVd-fragment-containing constructs indicated shuttling of the RNA into the nucleus by fragments as short as 80 nucleotides in length. Plant-to-plant variation in the timing of intron removal and subsequent GFP fluorescence was observed; however, earliest and most abundant GFP expression was obtained with constructs containing the conserved hairpin I paand embedded upper central conserved region. Our results suggest that this conserved sequence and/or the stem-loop structure it forms is sufficient for import of PSTVd into the nucleus. Asta Abraitiene http://digitalcommons.unl.edu/usdaarsfacpub/388 http://digitalcommons.unl.edu/usdaarsfacpub/388 Tue, 13 Oct 2009 13:30:17 PDT Host range expansion in insect herbivores is often thought to be mediated by several factors, principal among them are secondary plant metabolites. In weed biological control, the host range of a prospective agent is one of the most important considerations in its implementation. Extensive host testing tests seek to determine the behavioral acceptance and nutritional value of different test plant species to the potential agent. A list of test plants is compiled that comprises species that are close taxonomic relatives of the target weed plus other species of economic or ecologic importance. The host testing of the Melaleuca quinquenervia biological control agent Oxyops vitiosa indicated that larvae would accept and complete development on the Australian target weed M. quinquenervia, two Australian ornamental species, Callistemon citrina, Callistemon viminalis (all Myrtaceae). However, the larvae did not complete development when fed a North American species Myrica cerifera (Myricaceae). The study reported here confirms these results and examines the nutritional and performance differences in O. vitiosa larvae fed leaves of these species. The leaf quality factors, percent moisture, percent nitrogen, toughness, and terpenoid content were related to larval survival, performance and digestive indices. The results indicate that plant quality among the Myrtaceae species was generally similar and correspondingly larval survival, performance and digestive indices differed little when larvae were fed leaves of these species. However, significant differences occurred in the plant quality of the North American M. cerifera compared with the Australian species which had leaves with the lowest percent moisture, lowest leaf toughness, highest percent nitrogen. This species, however, is not a physiological host as none of the neonates survived to pupate. When third instars were switched to M. cerifera from their normal host M. quinquenervia reductions were found in survival, biomass gain, digestive efficiency, and conversion of digested food to insect biomass. The marginal acceptance of this North American native plant in laboratory bioassays appears related to the terpenoid chemistry that has similarities to the taxonomically unrelated host M. quinquenervia. However, the high larval mortality corresponds to several novel terpenoids that are not present in the host. For weed biological control host testing these results indicate that M. cerifera is a poor host for O. vitiosa. Additionally, future test plant lists should include plants with secondary metabolites similar to the target weed as these compounds may constitute behavioral cues that are relevant to these specialized herbivores. G. S. Wheeler http://digitalcommons.unl.edu/usdaarsfacpub/387 http://digitalcommons.unl.edu/usdaarsfacpub/387 Tue, 13 Oct 2009 13:20:50 PDT The Stethorini are unique among the Coccinellidae in specializing on mites (principally Tetranychidae) as prey. Consisting of 90 species in two genera, Stethorus and Parasthethorus, the tribe is practically cosmopolitan. The Stethorini are found in a diverse range of habitats, including many agricultural systems such as pome and stone fruits, brambles, tree nuts, citrus, avocadoes, bananas, papaya, palms, tea, cassava, maize, strawberries, vegetables, and cotton, as well as ornamental plantings, grasslands, forests, and heathlands. Tetranychid mite outbreaks became common in many agricultural systems only after World War II, when widespread use of broad-spectrum insecticides increased. Stethorini were initially appreciated only for their ability to suppress severe outbreaks of tetranychid populations. However, research on their prey searching behaviors reveals that Stethorini use visual and olfactory stimuli to locate small mite colonies in patchy distributions, and can be very effective in regulating their prey at low densities. Moreover, acariphagous coccinellids colonize mite outbreaks earlier, and consume more pest mites, than many other mite predators. Key to the use of coccinellids in conservation biological control programs is the provision of overwintering habitats and refuges from pesticides in and near cropland. When these conditions are fulfilled, Stethorini often play important roles in maintaining suppression of tetranychid populations. Examples of successful biological mite control with Stethorini include apple orchards in Pennsylvania, USA, and citrus in Asia, and the unintended disruption of a tetranychid-based biological control program for the invasive woody weed, gorse, in Australia and New Zealand. The systematics and taxonomy of this group is challenging with many cryptic species, and molecular diagnostic tools are sorely needed. How best to utilize their mite-suppressive potential in diverse settings requires better knowledge of their requirements including utilization of alternative foods, refuges for dormancy and from nonselective pesticides, and host-finding mechanisms. David J. Biddinger