68 DEVELOPMENT OF AN IRISH HIP FRACTURE DATABASE FRAILTY INDEX: ASSOCIATIONS WITH LENGTH OF STAY, DELIRIUM, MORTALITY AND NURSING HOME ADMISSION

Background

In older people, hip fracture can lead to adverse outcomes. Frailty, capturing biological age and vulnerability to stressors, can indicate those at higher risk. This study aimed to derive a frailty index (FI) in the Irish Hip Fracture Database (IHFD), to explore associations with prolonged length of hospital stay (LOS ≥ 30 days), delirium, inpatient mortality and new nursing home (NH) admission and to assess whether the FI added value to those predictions above and beyond age, sex, and pre-operative American Society of Anaesthesiology (ASA) score.

Methods

A 21-item FI was constructed with 16 dichotomous comorbidities, three 4-level ordinal pre-morbid functional variables (difficulty with indoor mobility, outdoor mobility, and shopping), and nursing home provenance (yes/no). The FI was computed as the proportion of items present, and divided into tertiles (low, medium, high risk). Independent associations between FI and outcomes were explored with logistic regression, from which we extracted adjusted Odds Ratios (aOR) and areas under the curve (AUC).

Results

From 2017-2020, the IHFD included 14,615 hip fracture admissions, mean (SD) age 80.4 (8.8), 68.9% women. Complete FI data was available for 12,502 (85.5%). By FI tertile (low to high risk), prolonged LOS proportions were 5.9%, 16.1% and 23.1%; delirium 5.5%, 13.5% and 17.6%; inpatient mortality 0.6%, 3.3% and 10.1%; and new nursing home admission 2.2%, 5.9% and 11.3%. All associations were statistically significant (p<0.001) independently of age and sex. AUC analyses suggested that the FI score, added to age, sex, and ASA score, added value to the prediction of delirium and new NH admission (p<0.05), and especially to prolonged LOS and inpatient mortality (p<0.001).

Conclusion

A 21-item FI in the IHFD was a significant predictor of outcomes and added value to traditional risk markers. The utility of a routinely derived FI to more efficiently direct limited orthogeriatric resources requires further investigation.

Cost of hospitalisation for hip fracture-findings from the Irish hip fracture database

The authors utilised the Irish Hip Fracture Database (IHFD) to quantify the impact of hip fracture on the health service in terms of incidence, bed days and financial costs. The absolute number of hip fracture cases recorded by the IHFD has increased, as has the associated costs of hospitalisation.

INTRODUCTION

Hip fracture places a considerable clinical and financial burden on the healthcare system, with acute hospitalisation accounting for a substantial proportion of the costs incurred. This paper aimed to quantify the cost of hospitalisation for hip fracture in Ireland in terms of bed days and direct hospital costs.

METHODS

The authors analysed 23,494 cases in the Irish Hip Fracture Database (IHFD) from 2014 to 2020. Case numbers and length of stay were analysed annually. Hospital costs for hip fracture were described using the 2020 Activity-Based Funding Price List, which outlines the fees paid to public hospitals for inpatient activity.

RESULTS

For the time period 2014-2020, the total cost of hospitalisation for hip fracture was approximately €296 million, equating to approximately €11,700 per episode of care. The annual cost of hospitalisation increased from approximately €34 million in 2014 to €44 million in 2020. In 2020, the mean length of stay for hip fracture was 17 days accounting for > 62,600 acute hospital bed days.

CONCLUSION

The absolute number of hip fracture cases recorded by the IHFD has increased, as has the cost of hospitalisation. Given the current capacity issues and economic constraints, there is a growing need to prioritise time spent in the most expensive acute hospital setting to the immediate perioperative period and maximise the use of community services and early supportive discharge for the rehabilitation phase.

Discharge destination after hip fracture: findings from the Irish hip fracture database

PURPOSE

Although home continues to be the place from which the majority of patients are admitted, less than one third of patients are Discharged Directly Home (DDH) following hip fracture. Once ready for discharge, DDH as opposed to Discharge to an Alternative Location (DAL), i.e., community care, rehabilitation facility or long-term care, is a high priority for patients and clinicians alike. Not only is DDH integral to the quality of life of patients, it is also an essential driver of the socioeconomic cost of hip fracture care.

METHODS

We analysed 21,819 cases in the Irish Hip Fracture Database from 2013 to 2019. Descriptive and analytical statistics were conducted.

RESULTS

29% (n = 6476) of patients were DDH during the study period. On multivariate analysis, the odds of DDH decreased as age increased (OR 0.28, p < 0.01, 95% CI 0.24-0.34). Patients who were independently mobile prior to fracture were 47% more likely to be DDH (OR 1.47, p < 0.01, 95% CI 1.29-1.68). Those mobilised early post operatively were 24% more likely to be DDH (OR 1.24, p < 0.01, 95% CI 1.06-1.45). Patients who waited > 72 h prior to surgery were 30% less likely to be DDH (OR 0.70, p < 0.01, 95% CI 0.56-0.88).

CONCLUSION

The authors identified patient characteristics that increased the likelihood of DDH, i.e., younger patients independently mobile prior to fracture, who received timely surgery and early post-operative mobilisation. The Irish Hip Fracture Standards (IHFS) incorporate 2 out the 3 modifiable factors identified, which reinforces the importance of the IHFS in improving patient outcomes.

Characteristics of Centenarians in the Irish Hip Fracture Database

Aim Hip fractures are common amongst older people and result in significant morbidity and mortality. The Irish Hip Fracture Database (IHFD) collects data, from the 16 trauma orthopaedic units in Ireland, on patients aged 60 years and older who sustain hip fractures. This study aims to describe the characteristics of those patients aged 100 years and older in this database. Methods A retrospective analysis of the IHFD from 2012 to 2017. Characteristics of those patients aged 100 years and over were collected and analysed. Results 57 patients were identified for inclusion, 52 (91%) of which were women. Mean age was 101, while mean length of stay was 22.6 days. 51 (89%) fractures were due to low velocity trauma, consistent with likely high rates of osteoporosis in this group. The great majority underwent operative intervention. 50 (88%) were discharged alive. Fracture type varied widely. Only 24 (42%) patients were documented to have been seen by a geriatrician during admission. There were low reported rates of co-morbid medical conditions, likely due to lack of recorded data, rather than true low rates of co-morbidities in this group. Discussion This study provides insight into this distinct group of people, with important implications for future healthcare planning and budgeting.

Trends in hip fracture care in the Republic of Ireland from 2013 to 2018: results from the Irish Hip Fracture Database

Hip fractures continue to be one of the most serious and costly injuries suffered by older people globally. This paper describes the development of a national hip fracture audit and summarises the first 6 years of data from the Republic of Ireland. This can help inform care, standards and outcomes of hip fracture patients.

INTRODUCTION

Ireland has one of the highest standardised rates of hip fracture in the world behind northern European countries. The Irish Hip Fracture Database (IHFD) was established in 2012 to drive clinical and organisational improvements in quality and effectiveness of hip fracture care. This paper describes the progression of the IHFD between 2013 and 2018 and identifies trends and areas for improvement.

METHODS

The IHFD is a clinically led, web-based audit, with data collected through the national Hospital Inpatient Enquiry (HIPE) electronic system, the principal source of information from publicly funded acute hospitals in Ireland. Eligible cases are aged ≥ 60 years with hip fracture as defined by IHFD or with other specified hip fracture excluding periprosthetic fractures. As of 2015, all 16 trauma-receiving hospitals within Ireland submitted data. Demographics and adherence to six national quality standards are described.

RESULTS

A total of 17,983 cases were included in the analysis. National coverage has increased from 63% in 2013 to 99% in 2018. Demographic characteristics are unchanged, but higher levels of comorbidity are seen. Internal fixation and hemiarthroplasty are the most common modes of surgical repair with two-thirds of cases receiving spinal rather than general anaesthesia. Increasingly patients are being assessed by a geriatrician (11% in 2013 to 69% in 2018) and receive a bone health assessment (65% in 2013 to 84% in 2018).

CONCLUSION

While some hip fracture standards have improved, further improvements are required to compare favourably internationally. Reduction of surgical delay and ensuring early mobilisation post-operatively are immediate priorities for the IHFD.

Predictors of in-hospital mortality post hip fracture in Ireland 2013-2017

Background

Hip fractures are associated with considerable mortality, morbidity and healthcare expenditure. There are approximately 3,500 hip fractures in Ireland per annum with this figure set to increase considerably over the coming years due to the ageing population. Internationally, mortality following hip fracture is approximately 10% at 1 month and 30% at 1 year, with less than half of survivors regaining their preoperative level of function. The authors aimed to identify the determinants of in-hospital mortality post hip fracture in the Republic of Ireland 2013-2017, with specific reference to the Irish Hip Fracture Standards.

Methods

A secondary analysis of 15,603 patients in the Irish hip fracture database was conducted.

Results

31% (n = 4,769) were male and 69% (n = 10,807) were female. Mean age for males was 75 years (SD 13.5) and 79 years for females (SD 10.5). The largest proportion of hip fractures occurred in the 80-89 age category, with 72.3% (n = 4,600) of these being female. Median in-hospital mortality was 4.7% (n = 711) (Range 2.7-6.2). Univariate logistic regression revealed 11 statistically significant predictors of in-hospital mortality; however, only 4 remained statistically significant on multivariate analysis [mobilised day of/after surgery (OR 1.46, 95% CI 1.25-1.70, p &lt; 0.000), pre-fracture mobility (OR 0.84, 95% CI 0.79-0.89, p &lt; 0.000), gender (OR 0.56, 95% CI 0.41-0.76, p &lt; 0.000) and age (OR 1.05, 95% CI 1.03-1.06, p &lt; 0.000)].

Conclusions

Older males with poor pre-fracture mobility who were not mobilised the day of/after surgery had the highest risk of in-hospital mortality. The ability to be mobilised on the day of/after surgery is a good composite measure of both patient and organisational factors in hip fracture care. This research supports the inclusion of mobilisation on the day of/after surgery as a new formal best practice standard.

Key messages

Patients not mobilised on the day of/after surgery are 46% more likely to die in hospital. In-hospital mortality of 4.7% in Ireland is comparable internationally. None of the IHFSs significantly influenced in-hospital mortality after multivariate analysis, but may well affect other outcomes such as ability to return home.

Soil Temperature Effects on the Interaction of Grape Rootstocks and Plant-parasitic Nematodes

Resistance to Meloidogyne spp. in commonly used resistant grape rootstocks is slightly compromised at soil temperatures above 27°C. Newly released UCD-GRN series rootstocks, which have broad nematode resistance, exhibit trace infections by Meloidogyne spp. at elevated temperature. Pathotypes of M. incognita and M. arenaria that are virulent on 'Harmony' rootstock, as well as M. incognita Race 3, which is avirulent on 'Harmony', failed to produce egg masses on the UCD-GRN series rootstocks and other resistant selections at 24°C. At 27°C and above, there was increased nematode galling and egg mass production; at 30°C, egg mass production levels of M. incognita Race 3 on 'Harmony' were up to 12% of that on susceptible 'Colombard' while reproduction of the virulent pathotypes on the UCD-GRN series was less than 5% of that on 'Colombard'. Resistance of several of the parental genotypes of the UCD-GRN rootstock series was slightly compromised at soil temperatures of 30°C and above; however, others maintained their resistance to even the virulent M. arenaria pathotype A at high temperatures. Effects of high temperature on resistance to Xiphinema index could not be assessed because of temperature sensitivity of the nematodes while resistance to Mesocriconema xenoplax was not compromised at high soil temperature. Resistance to Meloidogyne spp. in the UCD-GRN series rootstocks was not compromised when plants and nematodes were subjected to cyclical high and low temperature conditions, indicating that once initiated, the resistance mechanism is not reversed.

Resistance of Grape Rootstocks to Plant-parasitic Nematodes

Candidate grape rootstocks were selected through a rigorous screening program initiated with important sources of resistance to Meloidogyne pathotypes and to Xiphinema index in Muscadinia rotundifolia and Vitis species native to North America. Based on their rooting capability and horticultural characteristics, 200 candidates were selected from 5,000 progeny of multiple crosses between commercial grape rootstocks and wild grape species that exhibited resistance to nematodes. After a 15-year screening process, 13 selections emerged with either almost complete or complete combined resistance to M. incognita Race 3, M. incognita pathotype Harmony C, M. arenaria pathotype Harmony A, and X. index, important nematode pests of grapevines. Durability of this broad resistance was tested by challenging the selections with the target nematodes in combination and with the target nematodes in combinations with species not included in the screening process. Durability of resistance of the candidate rootstocks was also tested by exposure to the nematode communities of infested field soils from different locations. Breadth of resistance was determined on the basis of their host status to non-target nematodes, including Mesocriconema xenoplax, Pratylenchus vulnus, Tylenchulus semipenetrans and Paratylenchus hamatus. After a total of 204 separate trials, the rootstocks were released to the grape industry as UCD GRN1, UCD GRN2, UCD GRN3, UCD GRN4, and UCD GRN5. We provide a compilation of current knowledge of the host status of these five newly released rootstocks and of 27 other rootstock cultivars to plant-parasitic nematodes.

Pancreatico pleural fistula: an unusual complication of chronic pancreatitis

Pancreatico-pleural fistula secondary to chronic pancreatitis is a rare cause of pleural effusion. This case report presents a case of a middle aged female, a known case of chronic pancreatitis who presented with severe epigastric pain and progressive shortness of breath. CT and MRCP were useful in visualising the fistulous communication between the pancreas and pleural cavity. Treatment consisted of ERCP placement of a pancreatic stent, which facilitated internal drainage of pancreatic fluid thus resolving the pleural effusion and promoting healing of the fistula.

Population Characteristics and Dosage Trajectory Analysis for Mesocriconema xenoplax in California Prunus Orchards

The Mesocriconema xenoplax population increased exponentially in a newly planted peach orchard. The rate of increase was greater on Nemaguard than on Lovell rootstock and was reduced by postplant nematicides. Population levels were more stable in an established almond orchard on Nemaguard rootstock. All life stages of the nematode were present year round; lower ratios of juveniles to adults in summer suggested adverse effects of temperature and dry soil. Also in summer, there was a smaller proportion of the population in the upper 30 cm of soil than at greater depths. Nematode dosage, average nematode density multiplied by accumulated degree-days (physiological time) of the sampling interval, was useful in quantifying nematode stress on trees and as an indicator of the nematode management effectiveness. The annual trajectory of the nematode dosage could be determined by two samplings, one in spring and one in fall. A nematode predator, the parasitic fungus Hirsutella rhossiliensis, did not regulate ring nematode populations in the newly planted orchard; a recovery period was necessary for increase in the prevalence of parasitism.

Sensitivity of Meloidogyne javanica and Tylenchulus semipenetrans to Isothiocyanates in Laboratory Assays

ABSTRACT Isothiocyanates are released through enzymatic degradation of glucosinolates produced by plants in the family Brassicaceae. Glucosinolate profiles differ among plant species and the isothiocyanate derivatives differ in their toxicity to nematodes. Control of plant-parasitic nematodes in soil by isothiocyanates released from incorporated brassicaceous plant material has been inconsistent. Success might be improved with knowledge of the relative toxicities of various isothiocyanates against nematodes. Laboratory assays were conducted to determine lethal concentration (LC) values in sand of seven commercially available isothiocyanates against Tylenchulus semipenetrans and Meloidogyne javanica. The LC(90) values were 0.01 and 0.03 mumol/ml for 2-phenylethyl isothiocyanate and 0.48 and 0.35 mumol/ml for phenyl isothiocyanate for T. semipenetrans and M. javanica, respectively. Brassicaceous sources of benzyl or 2-phenylethyl isothiocyanate and, to a lesser extent allyl isothiocyanate, are the most promising candidates for plant-parasitic nematode management. The broader context of this research is the development of approaches for consistent and reliable use of plant-derived chemicals for nematode management. The strategy is to select plants in the family Brassicaceae based on their glucosinolate profiles and the sensitivity of the target nematode species to the associated isothiocyanates.

Plant sources of chinese herbal remedies: laboratory efficacy, suppression of Meloidogyne javanica in soil, and phytotoxicity assays

Extracts of Chinese herbal medicines from plants representing 13 families were tested for their ability to suppress plant-parasitic nematodes. Effective concentration (EC₅₀ and EC₉₀) levels for 18 of the extracts were determined in laboratory assays with Meloidogyne javanica juveniles and all stages of Pratylenchus vulnus. Efficacy of 17 extracts was tested against M. javanica in soil. Generally, EC₅₀ and EC₉₀ values determined in the laboratory were useful indicators for application rates in the soil. Extracts tested from plants in the Liliaceae reduced galling of tomato by M. javanica and were not phytotoxic. Similarly, isothiocyanate-yielding plants in the Brassicaceae suppressed root galling without phytotoxicity. Other plant extracts, including those from Azadirachta indica, Nerium oleander, and Hedera helix, suppressed root galling but were phytotoxic at the higher concentrations tested. Many of these plant sources have been tested elsewhere. Inconsistency in results across studies points to the need for identification of active components and for determination of concentration levels of these components when plant residues or extracts are applied to soil.

Relationship between crop losses and initial population densities of Meloidogyne arenaria in winter-grown oriental melon in Korea

To determine the economic threshold level, oriental melon (Cucumis melo L. cv. Geumssaragi-euncheon) grafted on Shintozoa (Cucurbita maxima x Cu. moschata) was planted in plots (2 x 3 m) under a plastic film in February with a range of initial population densities (Pi) of Meloidogyne arenaria. The relationships of early, late, and total yield to Pi measured in September and January were adequately described by both linear regression and the Seinhorst damage model. Initial nematode densities in September in excess of 14 second-stage juveniles (J2)/100 cm(3) soil caused losses in total yields that exceeded the economic threshold and indicate the need for fosthiazate nematicide treatment at current costs. Differences in yield-loss relationships to Pi between early- and late-season harvests enhance the resolution of the management decision and suggest approaches for optimizing returns. Determination of population levels for advisory purposes can be based on assay samples taken several months before planting, which allows time for implementation of management procedures. We introduce (i) an amendment of the economic threshold definition to reflect efficacy of the nematode management procedure under consideration, and (ii) the concept of profit limit as the nematode population at which net returns from the system will become negative.

Fatty acid composition and dynamics of selected fungal-feeding nematodes and fungi

Fatty acid profiles of fungal-feeding nematodes, Aphelenchus avenae and Aphelenchoides composticola, and selected fungi were determined in microcosm cultures of agar, broth, or sand amended with organic matter. Fatty acids of A. avenae and A. composticola included 16:0 18:0, 18:1omega7, 18:1omega9, 18:2, 20:0, 20:1, 20:2, 20:3 and 20:4 phospholipid fatty acids (PLFAs) and neutral lipid fatty acids (NLFAs). The nematodes differed in relative amounts of saturated and C(18) fatty acids. Similar C(16) and C(18) PLFAs and whole-cell fatty acids were found in Rhizoctonia solani, Fusarium oxysporum and Trichoderma sp. with 18:2omega6 as the major component. The C(20) fatty acids were not found in these fungi. Although only present in the nematodes, C(20) PLFAs were only detected when nematode population levels were > or =22 per gram of sand, suggesting that there is a detection threshold that might limit their use as biomarkers in the soil community. After removal of nematodes from a food source, the relative amount of C(20) PLFAs (structural components of nematode cell membranes) decreased more slowly than the C(16) and C(18) PLFAs, which may have reflected ingested fungal cytoplasm in the nematode intestine. In the early stage of organic matter decomposition, total and fungal PLFAs were lower in the presence of A. composticola then in its absence at C:N ratios > or =30:1.

Comparative demography of isogenic populations of Caenorhabditis elegans

Demographic characteristics of the bacterial-feeding nematode Caenorhabditis elegans were determined in two long-lived mutant strains, TJ1052 (age-1), CB4876 (clk-1), and a wild-type strain, N2. Within each strain, there was little correlation between longevity and reproduction for individuals that lived longer than 10days. Long-lived mutant strains produced fewer eggs than the wild type. Mean total life spans were 13.2days for the wild type, 21.9days for age-1, and 15.8days for clk-1; maximum life spans were 24days for the wild type, 47days for age-1, and 32days for clk-1. Differences in total life span resulted primarily from longer post-reproductive survival. The mean post-reproductive life spans were longer than the wild type by 183% in age-1 and 60% in clk-1. We conclude that (i) post-reproductive survival is not correlated with egg production within isogenic populations of C. elegans, and (ii) the relationship between reproduction and longevity differs among isogenic populations with specific longevity genes.

Plant Sources of Chinese Herbal Remedies: Effects on Pratylenchus vulnus and Meloidogyne javanica

More than 500 plant species, used alone or in combination, are documented in Chinese traditional medicine to have activity against helminth and micro-invertebrate pests of humans. We subjected 153 candidate medicines or their plant sources to multilevel screening for effectiveness against plant-parasitic nematodes. For extracts effective in preliminary screens, we determined time-course and concentration-response relationships. Seventy-three of the aqueous extracts of medicines or their plant sources killed either Meloidogyne javanica juveniles or Pratylenchus vulnus (mixed stages), or both, within a 24-hour exposure period. Of 64 remedies reported as antihelminthics, 36 were effective; of 21 classi- fied as purgatives, 13 killed the nematodes; of 29 indicated as generally effective against pests, 13 killed the nematodes. Sources of extracts effective against one or both species of plant-parasitic nematodes are either the whole plant or vegetative, storage or reproductive components of the plants. Effective plants include both annuals and perennials, range from grasses and herbs to woody trees, and represent 46 plant families.

Nematode community structure as a bioindicator in environmental monitoring

Four of every five multicellular animals on the planet are nematodes. They occupy any niche that provides an available source of organic carbon in marine, freshwater and terrestrial environments. Nematodes vary in sensitivity to pollutants and environmental disturbance. Recent development of indices that integrate the responses of different taxa and trophic groups to perturbation provides a powerful basis for analysis of faunal assemblages in soil as in situ environmental assessment systems.

Nematode-trapping fungi in organic and conventional cropping systems

ABSTRACT Nematode-trapping fungi, nematodes, and microbial biomass were quantified in conventionally and organically managed field plots in the Sustainable Agriculture Farming Systems Project at the University of California at Davis. There were four replicate plots (0.135 ha per plot) for each management system, and plots were sampled three times each year for 2 years. The hypothesis that nematode-trapping fungi would be more abundant in organically managed plots was partially supported: the number of species of nematode-trapping fungi was slightly but significantly greater in organic than in conventional plots, two species (Arthrobotrys dactyloides and Nematoctonus leiosporus) were detected more frequently in organic plots, and the population densities of A. dactyloides and N. leiosporus were greater in organic than in conventional plots. Two other species (A. haptotyla and A. thaumasia), however, tended to be more numerous in conventional than in organic plots, and the total density of nematode-trapping fungi was similar in organic and conventional plots. Bacterivorous nematodes were more abundant and microbial biomass (substrate-induced respiration) was greater in organic than in conventional plots. Suppression of the root-knot nematode Meloidogyne javanica, as measured in a bioassay, was not related to management system or population density of nematode-trapping fungi but was positively related to microbial biomass.

Decline in the incidence of late diagnosed congenital dislocation of the hip

INTRODUCTION

We reviewed the incidence of early and late diagnosed CDH over a 13 yr period in a single maternity with a well established follow-up program and a stable population base. In March 1991, all newborn infants were nursed in the lateral or supine position, having previously been nursed prone. In addition, a dedicated hip screener was appointed in October 1992. We wished to determine whether these changes could have led to a reduction in late diagnosed CDH.

METHODS

Babies with suspected CDH were seen by a single consultant orthopaedic surgeon within 1 week of birth. Splints were not applied until diagnosis was confirmed by the orthopaedic surgeon. The study period was from January 1983 to December 1995, inclusive.

RESULTS

37,383 babies were born during the study period, an average of 2,876 births per annum. The average rate of babies referred to the orthopaedic surgeon was 12.8 per 1,000 (range 5.5-28.2 per 1,000). The average incidence of babies splinted early was 7.19 per 1,000 (range 4.0-14.1 per 1,000) with no discernible increase or decrease over the yrs. In contrast, there was a clear reduction in the incidence of late diagnosed CDH; 42/24,713 births (January 1983-February 1992) compared to only 2/12,673 births (March 1992-December 1995; p < 0.0001. Twelve of the 44 infants (27 per cent) diagnosed with late diagnosed CDH were discovered by the policy of routine hip radiographs at 6 months of age of all babies born by breech presentation (2/12) or those with a positive family history of CDH in a first degree relative (10/12). Six others had a diagnosis of CDH confirmed by X-rays done at 6 months of age because of doubts about their examination in the newborn period.

CONCLUSIONS

Nursing infants in the supine or lateral position and the introduction of a single hip screener were associated with a reduction in the incidence of late diagnosed CDH. Routine hip radiographs of high risk infants at 6 months of age proved to be a valuable safety net in detecting a significant proportion of previously undetected infants with CDH.

Development and testing of an assay for soil ecosystem health using the bacterial-feeding nematode Cruznema tripartitum

Survival and respiration rates of the bacterial-feeding nematode Cruznema tripartitum after incubation in soil for 48 hr provided a useful bioassay of the presence and concentration level of biologically active toxicants. The assay provided an indication of toxicant activity at sublethal levels, and a means of determining when the toxicant had declined to levels not deleterious to physiological function. Assays of soil contaminants based on the community structure of resident soil nematodes were more useful in undisturbed soils than in agricultural soils where the range of taxa was relatively narrow. Assays involving measurement of survival and respiration rates of nematodes after immersion in an aqueous extract of contaminated soils were not useful due to degradation and loss of contaminant during the extraction process.

Sequential decision rules for managing nematodes with crop rotations

A dynamic model of nematode populations under a crop rotation that includes both host and nonhost crops is developed and used to conceptualize the problem of economic control. The steady state of the dynamic system is used to devise an approximately optimal decision policy, which is then applied to cyst nematode (Heterodera schachtii) control in a rotation of sugarbeet with nonhost crops. Long-run economic returns from this approximately optimal decision rule are compared with results from solution of the exact dynamic optimization model. The simple decision rule based on the steady state provides long-run average returns that are similar to the fully optimal solution. For sugarbeet and H. schachtii, the simplified rule can be calculated by maximizing a relatively simple algebraic expression with respect to the number of years in the sequence of nonhost crops. Maximization is easy because only integers are of interest and the number of years in nonhost crops is typically small. Solution of this problem indirectly yields an approximation to the optimal dynamic economic threshold density of nematodes in the soil. The decision rule requires knowledge of annual nematode population change under host and nonhost crops, and the relationship between crop yield and nematode population density.

Effect of Lime on Criconemella xenoplax and Bacterial Canker in Two California Orchards

In a peach orchard with an initial soil pH of 4.9, preplant application of 0, 13.2, 18.2, 27.3, or 54.2 kg lime/tree site altered soil pH (range after 1 year = 4.8-7.3) but did not affect numbers of Criconemella xenoplax or tree circumference. Liming also failed to reduce the incidence of bacterial canker, which affected 17% of the trees by the sixth year after planting. Four years after planting, numbers of C. xenoplax exceeded 400/100 cm(3) soil, regardless of treatment. Trees with higher densities of C. xenoplax had a higher incidence of canker. The nematophagous fungus Hirsutella rhossiliensis was not detected until the fourth year. Thereafter, the incidence of H. rhossiliensis and percentage C. xenoplax parasitized by H. rhossiliensis increased, but the increases lagged behind increases in numbers of nematodes. In an almond orchard with an initial soil pH of 4.6, preplant application of 0, 6.4, 12.8, or 25.0 kg lime/tree site altered soil pH (range after 1 year = 4.7-7.1). Numbers of C. xenoplax remained low (<20/100 cm(3) soil), whereas numbers of Paratylenchus sp. increased to high levels (>500/100 cm(3) soil), regardless of treatment. Low levels (<20/100 cm(3) soil) of H. rhossiliensis -parasitized Paratylenchus sp. were detected. No bacterial canker occurred, but tree circumference was greater after 6 years if soil pH was intermediate (6.0-7.0).

Competition between the Plant-parasitic Nematodes Pratylenchus neglectus and Meloidogyne chitwoodi

In experiments on competition between Pratylenchus neglectus and Meloidogyne chitwoodi in barley, the species that parasitized the roots first inhibited penetration by the latter species. Prior presence of P. neglectus impeded the development of M. chitwoodi. Pratylenchus neglectus reduced egg production, final population levels, and reproductive index of M. chitwoodi. The reduction was linearly related to initial population densities of P. neglectus. Initial population densities of M. chitwoodi had no effect on final population levels of P. neglectus. Carbon assimilation by barley plants was reduced when either nematode species was present alone, but not when both were present together. Both nematode species assimilated lower amounts of carbon when present together than when present alone. A split-root experiment demonstrated that translocatable chemicals were not involved in the competition between the two species.

Plant and soil nematodes: societal impact and focus for the future

Plant and soil nematodes significandy impact our lives. Therefore, we must understand and manage these complex organisms so that we may continue to develop and sustain our food production systems, our natural resources, our environment, and our quality of life. This publication looks specifically at soil and plant nematology. First, the societal impact of nematodes and benefits of nematology research are briefly presented. Next, the opportunities facing nematology in the next decade are outlined, as well as the resources needed to address these priorities. The safety and sustainability of U.S. food and fiber production depends on public and administrative understanding of the importance of nematodes, the drastic effects of nematodes on many agricultural and horticultural crops, and the current research priorities of nematology.

Parasitism of Nematodes by the Fungus Hirsutella rhossiliensis as Affected by Certain Organic Amendments

Experiments were conducted to determine whether the addition of organic matter to soil increased numbers of bacterivorous nematodes and parasitic activity of the nematophagous fungus Hirsutella rhossiliensis. In a peach orchard on loamy sand, parasitism of the plant-parasitic nematode Criconemella xenoplax by H. rhossiliensis was slightly suppressed and numbers of C. xenoplax were not affected by addition of 73 metric tons of composted chicken manure/ha. In the laboratory, numbers of bacterivorous nematodes (especially Acrobeloides spp.) and fungivorous nematodes increased but parasitism of nematodes by H. rhossiliensis usually decreased with addition of wheat straw or composted cow manure to a loamy sand naturally infested with H. rhossiliensis. These results do not support the hypothesis that organic amendments will enhance parasitism of nematodes by H. rhossiliensis.

Influence of Temperature and Host Plant on the Interaction Between Pratylenchus neglectus and Meloidogyne chitwoodi

The interaction between Pratylenchus neglectus (Pn) and Meloidogyne chitwoodi (Mc) was investigated at soil temperatures of 15, 20, and 25 C on barley and potato. Maximum numbers of Pn and Mc penetrated barley roots at 20 C, whereas a minimum number penetrated at 15 C. Pratylenchus neglectus restricted root penetration by Mc over time and vice-versa. Population densities of each species increased with increasing temperature. Concomitant inoculation of the two species resulted in lower numbers of Pn at 15 and 25 C in both barley and potato, whereas the numbers of Mc were lower at 15 C in barley and at 25 C in potato. Root weights of potato and barley at 15 and 20 C, respectively, were lowered by the presence of both nematodes singly or concomitantly. At 25 C, barley plants inoculated with Mc alone had lower shoot weight than uninoculated controls, but the damage was restricted when Pn also was present. The two species interact competitively, and the outcome varies with soil temperature and host plant. Pn has the potential to suppress Mc population levels and reduce the damage it causes to potato and barley.

Host Status of Selected Crops to Meloidogyne chitwoodi

Various crops were tested in greenhouse and field trials for their potential utility in the rotation sequence in the potato cropping system in Meloidogyne chitwoodi-infested soils of the Klamath Basin in northeastern California and southern Oregon. Two Solarium accessions from the International Potato Center in Peru were potential sources of resistance to M. chitwoodi. Cultivars of barley, oat, rye, wheat, and white lupine were maintenance hosts, supporting the nematode population at its current level without substantial increase or decline. Poor to nonhosts to race 1 of the nematode included cultivars of alfalfa, amaranth, oilseed radish, oilseed rape, and safflower. These crops have potential for inclusion in the cropping system but are subject to various constraints, including frost sensitivity and availability of markets. Sugarbeet, a new crop in the area, is a maintenance or better host of M. chitwoodi. Potato, tomato, and sunflower are excellent hosts.

New frontiers in nematode ecology

Future areas of emphasis for research and scholarship in nematode ecology are indicated by pressing agricultural and environmental issues, by new directions in applied nematology, and by current technological advances. Studies in nematode ecology must extend beyond observation, counting, and simple statistical analysis. Experimentation and the testing of hypotheses are needed for understanding the biological mechanisms of ecological systems. Opportunities for fruitful experimentation in nematode ecology are emerging at the ecosystem, community, population, and individual levels. Nematode ecologists will best promote their field of study by closely monitoring and participating in the advances, initiatives, developments, and directions in the larger field of ecology.

Sampling approaches for extensive surveys in nematology

Extensive surveys of the frequency and abundance of plant-parasitic nematodes over large geographic areas provide useful data of unknown reliability. Time, cost, and logistical constraints may limit the sampling intensity that can be invested at any survey site. We developed a computer program to evaluate the probability of detection and the reliability of population estimates obtained by different strategies for collecting one sample of 10 cores from a field. We used data from two fields that had been sampled systematically and extensively as the basis for our analyses. Our analyses indicate that, at least for those two fields, it is possible to have a high probability of detecting the presence of nematode species and to reliably estimate abundance, with a single 10-core soil sample from a field. When species were rare or not uniformly distributed in a field, the probability of detection and reliability of the population estimate were correlated with the distance between core removal sites. Increasing the prescribed distance between cores resulted in the composite sample representing a wider range of microenvironments in the field.

Effects of Temperature on Pratylenchus neglectus and on Its Pathogenicity to Barley

In a petri-dish study, development of the nematode Pratylenchus neglectus was observed every 4 days, and stage-specific development times were estimated, using a parameter estimation algorithm for a distributed-delay population model. The lower threshold temperature for development of a population of P. neglectus was 7.75 C. Temperatures above 25 C were unfavorable for this population on barley. Total numbers of P. neglectus in barley roots and associated soil in pots were greatest at 25 C and lower at temperatures above and below that level. There was no change in nematode numbers per gram of root as temperature increased between 24 C and 32 C because root weights decreased at higher temperatures. Restricted root mass may contribute to the lower total nematode population levels at higher temperature. Maximum number of nematodes moved through a 2-cm layer of sand on a Baermann funnel at about 20 C; lowest number of nematodes moved at 10 C and 30 C.

Stability and characteristics of spatial description parameters for nematode populations

The parameters of Taylor's Power Law (s(2) = am(b)) relating variance (s(2)) to mean population level (m) were acceptably stable in different fields with similar cropping systems. Values of both a and b parameters varied with nematode species. The value of a was a function of sample size (number of cores) and was characterized for each species. The value of b was stable across sample size and reflective of the life history strategy of the species. The relationship between the economic threshold and sampling intensity required to allow management decisions, with specified levels of risk, indicated the need for improved sampling technology.

Association of Verticillium chlamydosporium and Paecilomyces lilacinus with Root-knot Nematode Infested Soil

Population densities of Meloidogyne incognita and the nematophagous fungi, Paecilomyces lilacinus and Verticillium chlamydosporium, were determined in 20 northern California tomato fields over two growing seasons. Paecilomyces lilacinus was isolated from three fields, V. chlamydosporium was isolated from one field, and both fungi were isolated from 12 fields. Verticillium chlamydosporium numbers were positively correlated with numbers of M. incognita and P. lilacinus. Paecilomyces lilacinus numbers were positively correlated with V. chlamydosporium numbers, but they did not correlate with M. incognita numbers. The correlation coefficients were low (R < 0.5) but significant (P < 0.05). All P. lilacinus and V. chlamydosporium field isolates parasitized M. incognita eggs in vitro. In a greenhouse study, numbers of V. chlamydosporium and P. lilacinus increased more in soils with M. incognita-infected tomato plants than in soil with uninfected tomato plants. After 10 weeks, the Pf/ Pi of second-stage juveniles in soils infested with P. lilacinus, V. chlamydosporium, and M. incognita was 47.1 to 295.6. The results suggest V. chlamydosporium and P. lilacinus are not effectively suppressing populations of M. incognita in California tomato fields.

Meloidogyne incognita Survival in Soil Infested with Paecilomyces lilacinus and Verticillium chlamydosporium

Meloidogyne incognita-infected tomato seedlings were transplanted into sterilized soil or unsterilized soil collected from 20 California tomato fields to measure suppression caused by Paecilomyces lilacinus, Verticillium chlamydosporium, and other naturally occurring antagonists. Unsterilized soils Q, A, and H contained 35, 39, and 55% fewer M. incognita second-stage juveniles (J2) than did sterilized soil 1 month after infected tomato seedlings were transplanted to these soils and placed in a greenhouse. Three months after infected seedlings were transplanted to unsterilized or sterilized soil, unsterilized soils K, L, and Q had 97, 62, and 86% fewer J2 than the corresponding sterilized soils. Unsterilized soils of M. incognita-infected seedlings that were maintained 1 month in a greenhouse followed by 1 or 2 months of post-harvest incubation contained J2 numbers equal to, or greater than, numbers in the corresponding sterilized soil. The most suppressive of the unsterilized soils, K and Q, were not infested with V. chlamydosporium. Paecilomyces lilacinus and V. chlamydosporium increased in colony forming units in unsterilized soil of all bioassays, but they were not associated with lower numbers of J2.

Physiological Response of Resistant and Susceptible Vitis vinifiera Cultivars to Meloidogyne incognita

The effect of Meloidogyne incognita on growth, general physiological response, and the concentration of reducing and nonreducing sugars at the nematode feeding sites of French Colombard (susceptible) and Thompson Seedless (moderately resistant) Vitis vinifiera cultivars was studied up to 2,100 degree-days (DD-base 10 C). Nematode stress dosage, measured as the product of cumulative number of juveniles and females and their total energy (calories) demand, accounted for up to 15 and 10% of the energy assimilated by French Colombard and Thompson Seedless plants, respectively. Total leaf area, total carbon dioxide fixed, transpiration rate, stomatal conductance, and internal leaf CO concentration were not affected, but energy assimilated into plant tissue and respiration were decreased by nematode infection in both cultivars. Energy consumed by nematodes accounted for most of the difference in total energy assimilated between infected and uninfected plants on French Colombard but not on Thompson Seedless, suggesting that the resistant cultivar may be using more energy to curtail the nematode's activity. Nematodes did not affect the concentration of reducing sugars, but the concentration of nonreducing sugars increased in French Colombard and decreased in Thompson Seedless. This indicates that there was more translocation of photosynthate to the feeding sites of the susceptible than to those of the resistant cultivar, and may explain why M. incognita causes more damage to French Colombard than to Thompson Seedless.

Influence of Environmental Factors on the Hatch and Survival of Meloidogyne incognita

The influence of soil temperature and moisture on Meloidogyne incognita (Kofoid and White) Chitwood was examined in relation to hatching and survival of second-stage juveniles (J2). Nematodes were cultured on cotton (Gossypium hirsutum L. cv. Acala SJ2) under field conditions to provide populations similar to those found in the field in late autumn. Egg masses were placed in a temperature range (9-12 C and 21 C), and hatch was measured over a period equivalent to 20 degree days > 10 C (DD10). Hatch occurred below the reported 18 C activity threshold, was restricted below 12 C, and was inhibited below 10 C. Soil moisture influence on hatch was measured by placing egg masses in Hesperia sandy loam and subjecting them to suction pressures ranging from -1.1 bars to -4 .5 bars. Suction potentials of less than -2 bars reduced hatch and less than -3 bars inhibited hatch. J2 were placed in sandy loam soil with soil moisture near field capacity, and their motility was measured over a period of 500 DD10. In the absence of a host, more than 90% of J2 became nonmotile over this period.

Density-dependent parasitism of the soil-borne nematodeCriconemella xenoplax by the nematophagous fungusHirsutella rhossiliensis

Spatial sampling was used to investigate temporal density-dependent parasitism of the plant-parasitic nematodeCriconemella xenoplax byHirsutella rhossiliensis in three peach orchards on eight sample dates. The patches of soil in which the nematode and fungus interacted were assumed to possess similar density-dependent dynamics and to be small, independent, and asynchronous. Furthermore, sampling of separate patches was assumed to provide similar information with respect to density dependence as would temporal (repeated) sampling of the same patch. Percent parasitism was dependent on the number ofC. xenoplax/100 cm(3) soil (P=0.0001). The slope was unaffected by orchard or date but ranged from 0.0001 to 0.0043 depending on distance from the irrigation furrow. The relative shallowness of the slope and the large variation in percent parasitism not explained by nematode density suggest thatH. rhossiliensis is a weak regulator ofC. xenoplax population density.

Overwintering Stages of Meloidogyne incognita in Vitis vinifera

The overwintering of Meloidogyne incognita in and around Vitis vinifera cv. French Colombard roots was studied in a naturally infested vineyard at the Kearney Agricultural Center, in a growth chamber, in inoculated vines in microplots at the University of California, Davis, and in a greenhouse. Infected roots were sampled at intervals from onset of vine dormancy until plants accumulated about 800 degree days (DD - base 10 C). Embryogenesis within eggs, classified as less than or more than 16 cells and fully differentiated, and numbers of juveniles (second to fourth stage) and preovipositional and mature (egg-laying) adult stages in roots were determined. All stages were present at the onset of dormancy. Juveniles and immature females were not recovered during the dormant period. Mature females and eggs were always present in roots, although the number of mature females generally decreased with time after onset of dormancy. In contrast, in a greenhouse experiment that accumulated comparable DD without the host plant going through dormancy, the number of mature females increased. After bud break, the number of eggs per female increased and all nematode stages were found in host roots. Eggs in all stages of embryogenesis were observed at all times of sampling, indicating that females overwinter and are capable of laying eggs when conditions improve in the spring and need to be considered in nematode management decisions.

Impact of Meloidogyne incognita on Physiological Efficiency of Vitis vinifera

Four-week-old French Colombard plants rooted from green cuttings were inoculated with 0, 1,000, 2,000, 4,000, or 8,000 Meloidogyne incognita second-stage juveniles and maintained at 25 C night and 30 C day. Leaf area and dry weight and the rates of photosynthesis, stomatal conductance, and internal leaf CO concentration were measured at intervals up to 59 days after inoculation. Nematode stress dosage, measured as the product of cumulative number of juveniles and females and their total energy (calories) demand, was up to 3.4 kcal and accounted for up to 15% of the energy assimilated by the plants. There was a decline in the rate of leaf area expansion and leaf, stem, shoot, root (excluding nematode weight), and total plant dry weight with increasing nematode stress. Root weight including nematodes was not affected. Total respiration, plant photosynthesis, energy assimilated into plant tissue and respiration, and gross production efficiency decreased significantly with nematode stress. Photosynthetic rate, transpiration rate, stomatal conductance, and internal CO concentration were not affected. This study demonstrates that the energy demand for growth and reproduction of M. incognita accounts for a significant portion of the total energy entering the plant system. As a result, less energy is partitioned into leaf area expansion which, in turn, affects the energy entering the system and results in decreased productivity of nematode-infected grape vines.

Growth and Energy Demand of Meloidogyne incognita on Susceptible and Resistant Vitis vinifera Cultivars

Food (energy) consumption rates ofMeloidogyne incognita were calculated on Vitis vinifera cv. French Colombard (highly susceptible) and cv. Thompson Seedless (moderately resistant). One-month-old grape seedlings in styrofoam cups were inoculated with 2,000 or 8,000 M. incognita second-stage juveniles (J2) and maintained at 17.5 degree days (DD - base 10 C)/day until maximum adult female growth and (or) the end of oviposition. At 70 DD intervals, nematode fresh biomass was calculated on the basis of volumes of 15-20 nematodes per plant obtained with a digitizer and computer algorithm. Egg production was measured at 50-80 DD intervals by weighing 7-10 egg masses and counting the number of eggs. Nematode growth and food (energy) consumption rates were calculated up to 1,000 DD based on biomass increase, respiratory requirements, and an assumption of 60 % assimilation efficiency. The growth rate of a single root-knot nematode, excluding egg production, was similar in both cultivars and had a logistic form. The maximum fresh weight of a mature female nematode was ca. 29-32 mug. The total biomass increase, including egg production, also had a logistic form. Maximum biomass (mature adult female and egg mass) was 211 mug on French Colombard and 127 mug on Thompson Seedless. The calculated total cost to the host for the development of a single J2 from root penetration to the end of oviposition for body growth and total biomass was 0.535 and 0.486 calories with a total energy demand of 1.176 and 0.834 calories in French Colombard and Thompson Seedless, respectively.

Stage-specific Population Development and Fecundity of Paratrichodorus minor

A conceptual model of the life cycle of Paratrichodorus minor consisting of the egg stage, four juvenile stages, and the adult stage was proposed. Development of an individual from one stage to the next was described by a probability distribution defined by the mean length of time spent in the stage and the standard deviation associated with the mean duration. Experiments were conducted to estimate stage durations, stage-specific survivorships, and a fecundity rate for females. Eggs hatched on agar plates at a mean time of 53.3 +/- 7.3 degree-days using a basal threshold of 10 C (DD) with a range of 40-64 DD after deposition. Forty-five percent of the eggs observed ultimately hatched. Of the eggs that died, 44% died before the nematode form could be observed in the egg and 56% died after movement had been observed. First generation population peaks following inoculation with first-stage juveniles occurred at 28 DD for second-stage juveniles, 67 DD for third-stage juveniles, 109 DD for fourth-stage juveniles, and 143 DD for adults. Adult males are rare and were never observed in these studies. The fecundity rate was 0.784 eggs/(female-DD(1)), but the maximum length of the egg-laying period was not determined. The minimum egg-laying period was 73-113 DD, and minimum egg production was 57-86 eggs per female. The preovipositional period for adult females was estimated to be 79 DD. In the presence of a host, total population numbers increased, but in the absence of a host, the population declined to 33 % of the initial level after 300 DD.

Response of Soybean to Heterodera glycines Races 1 and 2 in Different Soil Types

Experiments were conducted for 3 years at four locations and 1 year with six soil types at a common location in North Carolina to determine damage and control-cost functions for Heterodera glycines races 1 and 2 on soybean. In the experiments on native loamy sand and sandy soils, tolerance limits for initial population densities were 0 or very low, whereas in a muck, the tolerance limit was 315 eggs/500 cm(3) soil. The aggressive race 2 was more damaging than race 1 in Lakeland sand and Norfolk loamy sand. The crop response was not different between races in the Appling sandy clay loam and Belhaven muck. Soybean yield responses to H. glycines were linear in six soil types in microplots at a common site. The amount of damage varied among these soil types, with lowest yields in the muck because of severe drought stress in this soil. An exponential function adequately described soybean yield response relative to nematode control with increasing rates of aldicarb in Norfolk loamy sand. Treatment with aldicarb in the Lakeland sand decreased the effective egg population of H. glycines but had only a minor effect in the muck.

Nematode-degree days, a density-time model for relating epidemiology and crop losses in perennials

The impact of Meloidogyne hapla on alfalfa (Medicago sativa) yield was described by a multiple point damage model as a function of current plant status, cumulative pest stress, and crop history. Nematode-degree days (NDD(female symbol)), calculated on a physiologic time scale as total area under the adult female population density curve, were used to express M. hapla parasitism as cumulative nematode dosage. NDD(female symbol) increased exponentially over physiological time at rates relative to M. hapla initial population density of eggs and second-stage juveniles (Pi). Dosage accumulation rates, varying from 213 to 272 NDD(female symbol) per degree day, did not differ (P = 0.05) among six Pi levels. Cumulative yield reductions, increasing linearly with NDD(female symbol) over time to 50% of the M. hapla-free controls, were well correlated for the six initial Pi levels (r(2) = 0.93). Progressive reductions in alfalfa yields to 65% of the nematode-free controls, reflective of the prolonged exposure of the crop to M. hapla, were adequately described by NDD model estimates of either combined population densities of eggs and juveniles or adult females. Cumulative area under the combined eggs (e) and juvenile (J) population curve (NDD(e+J)) and NDD(female symbol) were linearly related (r(2) = 0.97).

Influence of Alfalfa Plant Growth on the Multiplication Rates and Ceiling Population Density of Meloidogyne hapla

The rates of reproduction and multiplication of Meloidogyne hapla decreased as a result of self-regulatory, density-dependent processes with time and nematode population increase in the soil and roots of Medicago sativa cv. Cuf 101. Juvenile, egg, and mature female population densities increased at a maximum rate until damage to the host resulted in alfalfa yield reductions. Temporal differences in multiplication and reproduction rates of M. hapla were observed to be a function of initial population density (Pi), host damage, and root biomass, indicating increased levels of competition for a constant but limited number of feeding sites. Over time, a log linear relationship emerged between multiplication rate of M. hapla and Pi. Slopes of -0.90953 for combined eggs and juveniles and -0.71349 for mature females indicated a gradual approach to ceiling densities. Reproductive rates decreased exponentially from an initial maximal value of 200 to a relatively constant rate of 53 eggs per female.

Influence of Meloidogyne hapla on Alfalfa Yield and Host Population Dynamics

Self-thinning in alfalfa, a dynamic process involving the progressive elimination of the weakest plants, was enhanced by Meloidogyne hapla. Alfalfa stand densities decreased exponentially with time and were reduced 62% (P = 0.05) in the presence of M. hapla. As stand densities decreased over time, mean plant weights increased at a rate 2.59 times faster in the absence of M. hapla. In a stepwise multiple regression analysis, 65% of the total variation in yield could be explained by changes in stand density and 85% by average weight of individual stems. Alfalfa yields were suppressed (P = 0.05) by M. hapla, with suppression generally increasing with time and as the nematode population density increased. Yield suppression was attributable primarily to the decline in plant numbers and to suppression in individual plant weights.

Density-dependent nematode seasonal multiplication rates and overwinter survivorship: a critical point model

Nematode multiplication rates Pf/Pi and overwinter survivorship (Pi2/Pfl) for Meloidogyne incognita were both adequately described by negative exponential models, indicating density dependence in each case. Density dependence of the multiplication rates is mediated by resource limitation and host damage; in survivorship rates it may be mediated by limitation of stored reserves or prevalence of antagonists. Parameters of multiplication rate models were crop specific and varied with host status and environmental suitability. Maximum multiplication rates (a) of nearly 1,000 were measured for tomatoes. Equilibrium densities were sensitive to tolerance of the nematode by the crop. Overwinter survival rates varied among locations where cultural practices and length of infestation time differed.

Probability range in damage predictions as related to sampling decisions

The risk involved in basing a nematode management decision on predicted crop loss is related to the uncertainty in the crop damage function and error in measuring nematode population density. The sampling intensity necessary to measure a nematode population with specified precision varies with population density. Since the density is unknown prior to sampling, optimum sampling intensity for a management decision is calculated for the economic threshold population level associated with the management cost. Population densities below the threshold are measured with greater precision than required; those above the threshold are less precisely measured, but invoke management. The approach described provides resolution to sampling strategies and allows assessment of the risk associated with the management decision.