Entomopathogenic nematodes (Rhabditida: Steinernematidae and Heterorhabditidae) (EPNs) are generalist obligate pathogens present in the soil of most ecosystems. They have the potential to infect a broad host range, yet the potential for endemic EPNs to regulate soil-dwelling insect populations has received limited attention. We investigated the population dynamics of endemic EPNs to determine their ability to regulate annual bluegrass weevil (Listronotus maculicollis) (Coleoptera: Curculionidae) populations, a major pest of turfgrass in the northeastern United States. Weekly sampling of nematode and L. maculicollis populations was conducted in untreated fairway transects on three golf courses in New Jersey between April and October of 2006 and 2007. Steinernema carpocapsae and Heterorhabditis bacteriophora were found infecting all weevil stages from third instar to teneral adults. Both EPN species exhibited a distinct seasonality, appearing in high densities in the weeks immediately following high densities of first generation weevils in the soil. A positive temporal relationship was observed between densities of EPN-infected weevils and weevil stages between third instar and pupa, but L. maculicollis generational mortality due to EPN infection was highly variable between years and sites, ranging between 0 and 50%. Although infection densities and larval densities were positively correlated, per capita mortality did not increase with increased weevil densities. EPN distribution dynamically cycled between aggregated and uniform throughout the season across fairways. Few significant relationships were found to support the hypothesis that weevil spatial dispersion influences EPN spatial dispersion. The variability in EPN seasonal occurrence and generational impact on L. maculicollis together with the lack of spatial association with L. maculicollis suggest an inability of endemic EPN populations to reliably regulate weevil populations on golf course fairways. 相似文献
The Yucatán Peninsula of México has shallow soils and receives low amounts of precipitation, and has therefore low agricultural
potential. Lacking large-scale irrigation from rivers and adequate rainfall, the indigenous Maya groups maintain agricultural
productivity by adapting a variety of practices. Multistrata homegardens, one of their agricultural systems, have provided
goods for trade, sale and personal consumption for many centuries. Nevertheless, an understanding of the controlling biological
factors and interactions within these systems can lead to yield improvements. Photosynthetic rates, water use and litter production
for a variety of species have been studied in these gardens to determine how Maya management impacts resource flow, productivity
and diversity. When irrigated, diurnal photosynthetic rates nearly doubled for Manilkara zapota and water use increased two fold for M. zapota and Cordia dodecandra. Total litter production in traditional homegardens varied from 1,000 to 4,000 kg ha−1 yr−1 and ten arboreal species were found to contribute more than 33% of total litterfall biomass. Nutrient concentrations in the
leaves of the predominant species were analyzed; Meliococcusbijugatus and Spondias purpurea were found to contribute the largest quantities of N, P and C. Our research indicates that species and structural diversity
are critical to sustainability of homegardens, allowing efficient use and transfer of carbon, nutrients and water.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
New Forests - Permanent landscape attributes such as topography (elevation [m]) and microtopography (local variation in elevation [cm]) can increase the risk of cold air drainage down-slopes and in... 相似文献
Precision irrigation utilizing soil moisture data and valve-in head sprinkler systems may be a viable solution for sustainable water management on complex turfgrass areas. There is currently no research investigating the factors that influence soil moisture and turfgrass quality variability within sand-capped golf course fairways to aid in precision irrigation-related management decisions. Therefore, the objective of this study was to measure several turfgrass and soil characteristics from two sand-capped fairways during dry down events from either rainfall or irrigation to determine their relationship and contribution to soil moisture and turfgrass quality variability. Considerable spatiotemporal variability was observed within the two fairways during the dry down periods. Factors that were found to have a significant influence on soil moisture and turfgrass quality were sand capping depth, elevation, and thatch depth, but these relationships were not consistent between rainfall versus irrigation events, days after dry down, or even the specific fairways. Also, the direction of many of the relationships were opposite of what was expected. These findings highlight the complexity of soil moisture and turfgrass quality variability on sand-capped golf course fairways. To incorporate soil moisture sensor technologies into large-scale precision irrigation practices, mapping soil moisture with an understanding of contributing factors is a necessary preliminary step. Although there are several current practical limitations, the information presented in this study provides a foundation for future research.
Recurrent colic and unexplained weight loss despite good appetite and adequate feeding and management practices are common conditions in the horse. However, little information has been published on the systematic diagnostic evaluation, response to treatment, prognostic factors or outcome of either presentation. The aims of this study were to 1) identify possible prognostic indicators and 2) report the short- and long-term response to treatment with corticosteroid therapy of a variety of horses with a presumptive diagnosis of inflammatory bowel disease (IBD).Thirty-six horses with a history of recurrent colic and/or unexplained weight loss were screened with a detailed clinical, clinicopathological and diagnostic imaging examination. Twenty horses were subsequently selected that had findings consistent with inflammatory bowel disease based on the fulfilment of one or more of the following additional inclusion criteria: hypoproteinaemia, hypoalbuminaemia, malabsorption, an increased intestinal wall thickness on ultrasonographic examination or histopathological changes in rectal biopsy. These 20 horses were treated with a standardized larvicidal anthelmintic regime and a minimum of three weeks of corticosteroid therapy.
Results
The initial response to treatment was good in 75% (15/20) of horses, with a 3-year survival rate of 65% (13/20). The overall 3-year survival in horses that responded to initial treatment (12/15) was significantly higher (P = 0.031) than in those that did not respond to initial treatment (1/5). The peak xylose concentration was significantly (P = 0.048) higher in survivors (1.36 ± 0.44 mmol/L) than non-survivors (0.94 ± 0.36 mmol/L).
Conclusions
The overall prognosis for long-term survival in horses with a presumptive diagnosis of IBD appears to be fair to moderate, and the initial response to anthelmintic and corticosteroid therapy could be a useful prognostic indicator. The findings of the present study suggest that a low peak xylose concentration in absorption testing is associated with a less favourable prognosis, supporting the use of this test. 相似文献
The reproductive potential of males plays an important role in the productivity of captive penaeids. Males present a large variability in their reproductive potential, and thus the selection of appropriate males for reproduction is highly desirable. The present study compares sperm quality at the beginning of the experiment (baseline values) with variations in sperm quality as a result of consecutive spermatophore regenerations. This was done to evaluate possible predictive criteria for optimal sperm quality based on morphological and biochemical criteria in pond-reared Pacific white shrimp Litopenaeus vannamei males. Sperm quality was similar between left and right spermatophore. Sperm count and proportion of normal sperm increased by 86 and 65% (P < 0.05) respectively, from baseline values to third spermatophore regeneration. Proportion of dead sperm progressively decreased with consecutive regenerations, attaining values 33% lower by the third regeneration, compared to baseline values. This indicates that no decrease in sperm quality occurs in L. vannamei during consecutive regenerations and that the existing spermatophores at stocking of males should be expelled to have higher sperm quality in regenerated spermatophores. Furthermore, this procedure allows selecting individuals with high baseline sperm quality based on significant correlations between baseline and regenerated sperm quality observed in the present work. Baseline values of glucose concentration in the hemolymph were positively correlated to baseline values of sperm count (r = 03, P < 0.05). In contrast, baseline values of several lipids in the hemolymph were negatively correlated to several traits of sperm quality at first sampling (baseline values) or at first regeneration. These results are discussed in terms of nutritional requirements of males and of possible predictive criteria of sperm quality. 相似文献