Low Initial Population Research Articles

Structural elucidation and in vitro fermentation of extracellular α-d-glucan from Lactobacillus reuteri SK24.003

Abstract The molecular structure and its relationship to in vitro fermentation properties of α- d -glucan from Lactobacillus reuteri SK24.003 were investigated in this study. The chain structure was elucidated by 2D NMR spectroscopy and a possible repeating unit was deduced. During in vitro fecal fermentation, the relatively low initial bacterial population was observed during first 6 h incubation and small increase for α- d -glucan for 12–48 h incubation. A significant decrease in pH (approximately 2.0) was observed for fecal microbiota exposed to α- d -glucan. Acetic acid, propionic acid, n-butyric acid along with total short-chain fatty acid (SCFA) increased upon incubation, and d -glucan was initially fermented well resulting in the higher production of SCFA at 12 h. The n-butyric acid value at 48 h fermentation (1.29 mM) was higher than that of some commercial prebiotic oilosaccharides. These results suggested that α- d -glucan might be efficiently utilized by gut bacteria and may have a positive effect for gastrointestinal health.

Modelling the effect of demographic traits and connectivity on the genetic structuration of marine metapopulations of sedentary benthic invertebrates

AbstractAccounting for connectivity is essential in marine spatial planning and the proper design and management of marine protected areas, given that their effectiveness depends on the patterns of dispersal and colonization between protected and non-protected areas. The genetic structure of populations is commonly used to infer connectivity among distant populations. Here, we explore how population genetic structure is affected by pre- and settlement limitations with a spatially explicit coupled metapopulation-gene flow model that simulates the effect of demographic fluctuations on the allele frequencies of a set of populations. We show that in closed populations, regardless of population growth rate, the maintenance of genetic diversity at saturating initial population density increases with species life expectancy as a result of density-dependent recruitment control. Correlatively, at low initial population density, the time at which a population begins to lose its genetic diversity is driven larval and post-settlement mortality (comprised in the recruitment success parameter)—the larger the recruitment success, the stronger the genetic drift. Different spatial structures of connectivity established for soft bottom benthic invertebrates in the Gulf of Lions (NW Mediterranean, France) lead to very different results in the spatial patterns of genetic structuration of the metapopulation, with high genetic drift in sites where the local retention rate was larger than 2%. The effect of recruitment failure and the loss of key source populations on heterozygosity confirm that transient demographic fluctuations help maintain genetic diversity in a metapopulation. This study highlights the role of intraspecific settlement limitations due to lack of space when the effective number of breeders approaches saturating capacity, causing a strong reduction in effective reproduction. The present model allows to: (i) disentangle the relative contribution of local demography and environmental connectivity in shaping seascape genetics, and (ii) perform in silico evaluations of different scenarios for marine spatial planning.

Linking resource selection and mortality modeling for population estimation of mountain lions in Montana

To be most effective, the scale of wildlife management practices should match the range of a particular species’ movements. For this reason, combined with our inability to rigorously or regularly census mountain lion populations, several authors have suggested that mountain lions be managed in a source-sink or metapopulation framework. We used a combination of resource selection functions, mortality estimation, and dispersal modeling to estimate cougar population levels in Montana statewide and potential population level effects of planned harvest levels. Between 1980 and 2012, 236 independent mountain lions were collared and monitored for research in Montana. From these data we used 18,695 GPS locations collected during winter from 85 animals to develop a resource selection function (RSF), and 11,726 VHF and GPS locations from 142 animals along with the locations of 6343 mountain lions harvested from 1988–2011 to validate the RSF model. Our RSF model validated well in all portions of the State, although it appeared to perform better in Montana Fish, Wildlife and Parks (MFWP) Regions 1, 2, 4 and 6, than in Regions 3, 5, and 7. Our mean RSF based population estimate for the total population (kittens, juveniles, and adults) of mountain lions in Montana in 2005 was 3926, with almost 25% of the entire population in MFWP Region 1. Estimates based on a high and low reference population estimates produce a possible range of 2784 to 5156 mountain lions statewide. Based on a range of possible survival rates we estimated the mountain lion population in Montana to be stable to slightly increasing between 2005 and 2010 with lambda ranging from 0.999 (SD=0.05) to 1.02 (SD=0.03). We believe these population growth rates to be a conservative estimate of true population growth. Our model suggests that proposed changes to female harvest quotas for 2013–2015 will result in an annual statewide population decline of 3% and shows that, due to reduced dispersal, changes to harvest in one management unit may affect population growth in neighboring units where smaller or even no changes were made. Uncertainty regarding dispersal levels and initial population density may have a significant effect on predictions at a management unit scale (i.e. 2000km2), while at a regional scale (i.e. 50,000km2) large differences in initial population density result in relatively small changes in population growth rate, and uncertainty about dispersal may not be as influential. Doubling the presumed initial density from a low estimation of 2.19 total animals per 100km2 resulted in a difference in annual population growth rate of only 2.6% statewide when compared to high density of 4.04 total animals per 100km2 (low initial population estimate λ=0.99, while high initial population estimate λ=1.03). We suggest modeling tools such as this may be useful in harvest planning at a regional and statewide level.

Pushed beyond the brink: Allee effects, environmental stochasticity, and extinction

To understand the interplay between environmental stochasticity and Allee effects, we analyse persistence, asymptotic extinction, and conditional persistence for stochastic difference equations. Our analysis reveals that persistence requires that the geometric mean of fitness at low densities is greater than one. When this geometric mean is less than one, asymptotic extinction occurs with high probability for low initial population densities. Additionally, if the population only experiences positive density-dependent feedbacks, conditional persistence occurs provided the geometric mean of fitness at high population densities is greater than one. However, if the population experiences both positive and negative density-dependent feedbacks, conditional persistence only occurs if environmental fluctuations are sufficiently small. We illustrate counter-intuitively that environmental fluctuations can increase the probability of persistence when populations are initially at low densities, and can cause asymptotic extinction of populations experiencing intermediate predation rates despite conditional persistence occurring at higher predation rates.

Life cycle and damage of the root-knot nematode Meloidogyne minor on potato, Solanum tuberosum

Meloidogyne minor is a root-knot nematode reported in Belgium, Ireland, The Netherlands, Portugal, United Kingdom, Chile and the United States. It is found in sport fields and golf courses where it causes the yellow patch disease. However, M. minor has also been detected in potato fields in The Netherlands and the UK and may pose a threat for potato cultivation. Therefore, the life cycle and damage of M. minor on potato cv. Bintje were examined under controlled conditions. To assess its life cycle, young potato plants were inoculated with freshly hatched second-stage juveniles (J2). The developmental stages of M. minor were recorded at weekly intervals after inoculation until second generation J2 were detected. One week after inoculation, only vermiform juveniles were found in the roots. All juveniles were swollen after 3 weeks and the first adult females were observed. Egg masses were seen after 6 weeks together with second generation J2. The number of degree days for M. minor to complete its life cycle was calculated using a base temperature of 5°C (DD5); between 606 and 727 DD5 were needed to complete the life cycle. Damage development of M. minor on potato was examined in a pot experiment with different inoculation densities. Symptoms (galling on the tubers) were similar to those caused by M. chitwoodi and M. fallax. At initial population densities () of 10 J2 (100 cm3 soil)−1 and more, tubers showed galls. Severely damaged potato tubers were observed at (100 cm3 soil)−1 and a damage threshold of 41 J2 (100 cm3 soil)−1 was calculated. An in vitro test showed that five, commonly grown, potato cultivars were good hosts for M. minor. Based on our results, M. minor is able to develop on potato and cause severe damage at low initial population densities. Therefore, further spread of this nematode in agricultural fields should be avoided.

Stress response in Pectobacterium atrosepticum SCRI1043 under starvation conditions: adaptive reactions at a low population density

The adaptive reactions of plant pathogenic bacterium Pectobacterium atrosepticum SCRI1043 under starvation conditions were studied. The main emphasis was given to the peculiarities of stress responses depending on the bacterial population densities. When bacteria were subjected to starvation at high population densities (107–109 CFU ml−1), their adaptive reactions conformed to the conventional conception of bacterial adaptation related to autolysis of part of the population, specific modification of cell ultrastructure, activation of expression of stress responsive genes and acquiring cross protection against other stress factors. In contrast, at low initial population densities (103–105 CFU ml−1), as described in our recent work, the cell density increased due to multiple cell division despite the absence of exogenous growth substrate. Here we present data that demonstrate that such unconventional behavior is part of a stress response, which provides increased stress tolerance while retaining virulence. Cell morphology and gene expression in high- and low-cell-density starving Pba cultures were compared. Our investigation demonstrates the existence of alternative adaptive strategies enabling pathogenic bacteria to cope with a variety of stress factors, including starvation, especially necessary when residing outside of their host.

Differential sorting of individuals in territorial species affects apparent habitat quality

Territoriality leads to non-random sorting of individuals into habitats of differing quality. This can affect empirical estimates of population growth rate (λ), a measure of habitat quality, such that habitat-specific λ varies with population size. I present a simple model of territorial behavior in which territory acquisition depends on age and individual vigor. Under this model, with a low initial population, the λ associated with the best habitat stays constant until all territories are full. At that point, as less competitive individuals move to secondary habitat, the λ value in the better habitat increases. Similarly, as secondary habitat becomes occupied by individuals of successively greater vigor, λ can switch from a sink (λ 1). This means that habitat quality is not a fixed quantity but results from an interaction of the characteristics of the habitat with competitive sorting of individuals. If all individuals are in a good habitat, its conservation value will be underestimated and likewise the value of secondary habitat may not be properly assessed. © 2013 The Wildlife Society.

Efficacy of Entomopathogenic <I>Steinernema</I> and <I>Heterorhabditis</I> Nematodes Against White Grubs (Coleoptera: Scarabaeidae) in Peanut Fields

The efficacy of entomopathogenic nematodes (EPNs) against the white grub Holotrichia parallela Motschulsky (Coleoptera: Scarabaeidae) in the peanut (Arachis hypogaea L.) fields was evaluated. In the first experiment with a high initial white grub population (24.65 +/- 2.44 larvae per m2) in the field, Steinernema longicaudum X-7 and Heterorhabditis bacteriophora H06 at 10,000 and 5,000 infective juveniles (IJs) per plant contributed to significantly higher percentage reduction of the white grub larvae, lower percentage of the injured legume, and higher peanut yield compared with chlorpyrifos and other treatments. The peanut yields harvested from the plots treated with EPNs at 5,000 IJs per plant were at least 70% higher than that from the untreated control (water) and at least 30% higher than that from chlorpyrifos-treated plots. In the second experiment with a low initial white grub population (8.07 +/- 1.29 larvae per m2) in the field, EPN treatment did not increase peanut yield compared with the other treatments. But both S. longicaudum X-7 and H. bacteriophora H06 gained higher percentage reduction of the white grub larvae and lower percentage of the injured legume than Steinernema carpocapsae (Weiser) All and the control. The cost-benefit of using EPNs for white grub control was estimated to be comparable with that of using chemicals. S. longicaudum X-7 and H. bacteriophora H06 showed promise for white grub control in peanut fields.

Strain origin drives virulence and persistence ofXylella fastidiosain alfalfa

Generalist pathogens frequently exist as a complex of genetically differentiated strains, which can differ in virulence and transmissibility. A description of the extent to which strain variability mediates host species competence is needed to understand disease dynamics for systems with both host and pathogen strain diversity. This study tested the hypothesis that strain‐specific variation of a generalist vector‐borne plant pathogen,Xylella fastidiosa, affects disease severity in alfalfa (Medicago sativa) and competence of this crop as a reservoir host. Alfalfa seedlings were inoculated with one of 23X. fastidiosaisolates collected from different hosts, eight identified as belonging to an almond strain, and the remainder from a grape strain. Pathogen population, symptom severity and infection incidence were compared over five successive harvests. Infected plant size, measured mainly by plant height, internode length and above ground biomass, was reduced up to 50% compared to buffer‐inoculated controls, and more severe symptoms were observed at later harvests and for higher pathogen populations. Grape isolates had higher bacterial populations within alfalfa than almond isolates. In addition, infection with grape isolates resulted in more severe alfalfa stunting than that caused by almond isolates. Moreover, there was a strong positive relationship between isolate multiplication rate and both symptom severity and infection persistence (i.e. maintenance of chronic infection within host). Isolates with low initial populations had low incidence at the final harvest, with one isolate dying out altogether. The results showed thatX. fastidiosa‐genetic diversity contributed to variation in alfalfa disease severity. The results also suggest that pathogen strain may mediate host competence via differences in bacterial population density and persistence.

Intra- and Interspecific Competition for Nutrients and Light in Diatom Cultures

ABSTRACT Intra- and interspecific competition of clonal populations of Achnanthidium minutissimum and two potential competitors (Cocconeis Placentula var. lineata and Cymbella cistula) were examined in laboratory experiments. Growth rate of A. minutissimum was compared at low and high initial population densities and when in competition with C. p.lineata or C. cistula. In addition, four treatment combinations of nutrients and light were used. Intraspecific rather than interspecific competitive effects regulated A. minutissimum growth rates. C. p. lineata grew very slowly in cultures. C. cistula grew well in culture, formed stalks, and overgrew A. minutissimum. Facilitation by C. cistula stalks, providing substratum for colonization, may have countered interspecific competition on A. minutissimum.

Reproductive performance of the great cormorant (Phalacrocorax carbo sinensis) in three Greek colonies

Several breeding parameters of the great cormorant (Phalacrocorax carbo sinensis) were studied in Greece in 2001 and 2002 and were found to be generally higher at Lake Kerkini than in the other colonies. Fledging success (proportion of hatched eggs that led to fledged nestlings) was significantly higher at Lake Kerkini and in the Axios Delta in both years than at Lake Mikri Prespa in 2002. Mean fledgling production (the number of young fledged per initiated clutch) was significantly higher at Lake Kerkini than at Lake Mikri Prespa in 2002. The high fledgling production (2.15–2.75 fledglings on average in this study), the high food availability and the low initial population density allowed the total Greek breeding population to grow at a fast rate (19.0% per annum) in the 1990s. Given the scarcity of information on great cormorant nesting in Greece, basic breeding parameters are important for modelling population dynamics.

Quality damage on carrots (Daucus carota L.) caused by the root-knot nematode Meloidogyne chitwoodi

AbstractIn the Belgian provinces Antwerp and Limburg, the root-knot nematode, Meloidogyne chitwoodi, is widespread. These regions are important production areas of carrot, Daucus carota, for the processing industry. Nineteen carrot cultivars were screened for potential resistance for M. chitwoodi. Egg masses of M. chitwoodi were found on all cultivars. However, there were no egg masses on more than 80% of plants of cvs Berlanda, Bolero, Chantenay, Nantucket and Parmex. By contrast, on cvs ABK, Douceur, Maxi and Merida egg masses were formed on all of the tested plants. To gain information about the damage caused by M. chitwoodi, carrots were grown in soil infected with different densities of nematodes. There was no effect of M. chitwoodi on the length, width and weight of the carrot taproot. Damage caused by M. chitwoodi was manifested by severe galling near the lenticels. Inoculation of nematodes 6 weeks after the carrots emerged resulted in a higher percentage of infected carrots and damaged taproots compared with earlier inoculation times. The effect of the time of harvest on nematode infection and damage was examined. When harvested 100 days after sowing in soil with low nematode densities (two second-stage juveniles (J2)/100 g soil), no damage was reported. Harvesting 120 and 140 days after sowing resulted in 10 and 20% damaged carrots, respectively. With initial M. chitwoodi densities of 25 J2/100 g soil, the percentage of damaged taproots increased from 10% when harvested 100 days after sowing to 70% when harvested 140 days after sowing. In a field trial, 11.5% of the carrots were damaged after a field period of 139 days and the initial M. chitwoodi population increased from 3 to 111 J2/100 g soil. It is recommended that growing carrots in M. chitwoodi-infested fields should be avoided. However, damage can be limited in fields with low initial nematode populations when the growing period is reduced.

Evaluation of Long-Term Mating Disruption of Ephestia kuehniella and Plodia interpunctella (Lepidoptera: Pyralidae) in Indoor Storage Facilities by Pheromone Traps and Monitoring of Relative Aerial Concentrations of Pheromone

The potential for pheromone-based mating disruption (MD) of Ephestia kuehniella (Walker) and Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae) was investigated in two flour mills and a pet food distributor. Plastic sachets emitting 2–3 mg per d (Z,E)-9,12-tetradecadienyl acetate, the major pheromone component of both moth species, were used as MD dispensers, which were applied in grid systems resulting in one dispenser per 100 m3 of air volume. Pheromone traps with sticky inserts were used to monitor moth population fluctuations. To monitor pheromone levels in the air before, during, and after the treatment, electroantennographic (EAG) measurements were performed using a portable device. All localities showed decreased trap catches after application of MD. In two localities with low initial population densities, trap catches were reduced immediately after application of MD and remained very low, even several months after the MD treatment was terminated. In contrast, in a locality with a higher initial population density the reduction in trap catches was slower, and trap catches increased again soon after the termination of the MD treatment. Electrophysiological data showed not only increased aerial levels of pheromone during the treatment period but also levels that were higher than during pretreatment, even 12 mo after removal of MD dispensers. The localities had good ventilation, and the memory effect observed indicates that the pheromone adhered to surfaces that subsequently functioned as secondary dispensers. Customer complaints registered by one of the mills were 49% less in 2004, after 2 yr of MD compared with 2002, the year before the treatments began.

Evaluation of Long-Term Mating Disruption of <I>Ephestia kuehniella</I> and <I>Plodia interpunctella</I> (Lepidoptera: Pyralidae) in Indoor Storage Facilities by Pheromone Traps and Monitoring of Relative Aerial Concentrations of Pheromone

The potential for pheromone-based mating disruption (MD) of Ephestia kuehniella (Walker) and Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae) was investigated in two flour mills and a pet food distributor. Plastic sachets emitting 2-3 mg per d (Z,E)-9,12-tetradecadienyl acetate, the major pheromone component of both moth species, were used as MD dispensers, which were applied in grid systems resulting in one dispenser per 100 m(3) of air volume. Pheromone traps with sticky inserts were used to monitor moth population fluctuations. To monitor pheromone levels in the air before, during, and after the treatment, electroantennographic (EAG) measurements were performed using a portable device. All localities showed decreased trap catches after application of MD. In two localities with low initial population densities, trap catches were reduced immediately after application of MD and remained very low, even several months after the MD treatment was terminated. In contrast, in a locality with a higher initial population density the reduction in trap catches was slower, and trap catches increased again soon after the termination of the MD treatment. Electrophysiological data showed not only increased aerial levels of pheromone during the treatment period but also levels that were higher than during pretreatment, even 12 mo after removal of MD dispensers. The localities had good ventilation, and the memory effect observed indicates that the pheromone adhered to surfaces that subsequently functioned as secondary dispensers. Customer complaints registered by one of the mills were 49% less in 2004, after 2 yr of MD compared with 2002, the year before the treatments began.

Moving to High Quality of Life

The U.S. population has been migrating to places with high perceived quality of life. A calibrated general-equilibrium model shows that such migration follows from broad-based technological progress. Rising national wages increase demand for consumption amenities. Under a baseline parameterization, a place with amenities for which individuals would pay 5 percent of their income grows 0.3 percent faster than an otherwise identical place. Productivity is shown to be a decreasingly important determinant of local population. The faster growth of high-amenity places is considerably strengthened if they have low initial equilibrium population density underpinned by low relative productivity. Places with identical amenities asymptotically converge to an identical population density, regardless of their relative productivity levels. An implication is that the high growth rates of high-amenity localities should eventually taper off.

Host–parasite relationships of Meloidogyne incognita on spinach

Host–parasite relationships in root‐knot disease of spinach caused by Meloidogyne incognita race 1 were studied under glasshouse conditions. Nematode‐induced mature galls were large and usually contained one or more females and egg masses with eggs. Feeding sites were characterized by the development of giant cells containing granular cytoplasm and many hypertrophied nuclei. The cytoplasm in these giant cells was aggregated alongside the thickened cell walls. Stelar tissues within galls appeared disorganized. The relationship between initial nematode population density (Pi) in a series from 0–128 eggs and second‐stage juveniles per cm3 soil and growth of spinach cv. Symphony F1 seedlings was tested under glasshouse conditions. A Seinhorst model [y = m + (1 − m)zP–T] was fitted to fresh top‐ and total plant‐weight data for inoculated and control plants. Tolerance limits (T) of spinach cv. Symphony F1 to M. incognita race 1 for fresh top and total plant weights were 0·25 and 0·5 eggs and second‐stage juveniles per cm3 soil, respectively. The minimum relative values for fresh top and total plant weights were zero in both cases at Pi ≥ 32 eggs and second‐stage juveniles per cm3 soil. Root galling was least at low initial population densities and greatest at 16 eggs and second‐stage juveniles per cm3 soil. Maximum nematode reproduction rate was 33·1‐fold at the lowest Pi.

Influence of agitation, inoculum density, pH, and strain on the growth parameters of Escherichia coli O157:H7—relevance to risk assessment

Foods may differ in at least two key variables from broth culture systems typically used to measure growth kinetics of enteropathogens: initial population density of the pathogen and agitation of the culture. The present study used nine Escherichia coli O157:H7 strains isolated from beef and associated with human illness. Initial kinetic experiments with one E. coli O157:H7 strain in brain–heart infusion (BHI) broth at pH 5.5 were performed in a 2×2×3 factorial design, testing the effects of a low (ca. 1–10 colony-forming units [CFU]/ml) or high (ca. 1000 CFU/ml) initial population density, culture agitation or no culture agitation, and incubation temperatures of 10, 19, and 37 °C. Kinetic data were modeled using simple linear regression and the Baranyi model. Both model forms provided good statistical fit to the data (adjusted r 2>0.95). Significant effects of agitation and initial population density were identified at 10 °C but not at 19 or 37 °C. Similar growth patterns were observed for two additional strains tested under the same experimental design. The lag, slope, and maximum population density (MPD) parameters were significantly different by treatment. Further tests were conducted in a 96-well microtiter plate system to determine the effect of initial population density and low pH (4.6–5.5) on the growth of E. coli O157:H7 strains in BHI at 10, 19, and 37 °C. Strain variability was more apparent at the boundary conditions of growth of low pH and low temperature. This study demonstrates the need for growth models that are specific to food products and environments for plausible extrapolation to risk assessment models.

Spatial variation in net nitrate production in a N-saturated coniferous forest soil

In this study the spatial variation in nitrate and ammonium production was investigated within a Scots pine forest soil. Geostatistical analysis using isopleths was used to determine spatial clustering of biological activity. The effect of inhibiting and limiting substances was tested to explain locally low nitrification. Nitrate and ammonium were determined in leachates from intact soil cores, collected from a 20×20 m 2 homogeneous plot in a Scots pine forest. These cores were incubated under controlled conditions (constant temperature and moisture) and leachable inorganic nitrogen concentrations were determined after 3 weeks incubation at 18 °C. Both nitrate and ammonium leaching showed high spatial variation (coefficient of variation 75 and 52%, respectively). Possible limitation in low nitrate producing columns was investigated after addition of nutrients. Leachate from low nitrate leaching columns was added to high nitrate producing columns to test for water-soluble inhibiting factors of nitrate production. A mixture of phenols was added to high nitrate producing columns. Low nitrate leaching was not significantly increased by addition of nutrients compared to the control and the addition of leachate or phenols did not decrease net nitrate production compared to the control. A significant negative correlation was found between organic carbon and nitrate leaching, suggesting that denitrification was important at sites with low nitrate leaching. No significant differences were observed in nitrate leaching from cores at the end of the incubation compared to high initial variation. This indicates that low initial populations of nitrifiers could have been responsible for low nitrate production.

Detection and Isolation of Listeria monocytogenes from Food Samples: Implications of Sublethal Injury

Detection of L. monocytogenes is often limited by the performance of the enrichment media used to support bacterial growth to detectable levels. Because Listeria may exist at extremely low levels in foods, sample enrichment protocols must amplify these low initial populations to detectable limits. Listeria may also exist in an injured state in food products as a result of processing treatments such as heating, freezing, exposure to acids, or exposure to sanitizing compounds. Selective agents in enrichment media normally used for recovery of Listeria may inhibit repair and detection of sublethally injured Listeria, which may go on to repair, grow, and regain pathogenicity. Simple modifications to existing regulatory protocols, such as those that use more than one enrichment broth, raise sensitivity of detection to 90%. This review shows the efficacy of repair/enrichment strategies, which increase sensitivity of detection to 97.5-98.8% compared with 65-70% by standard regulatory protocols. Ribotype analysis of isolates obtained from meat samples reveals a complex microbial ecology, with striking differences in both number and distribution of distinct genetic types of Listeria, depending upon whether samples are enriched in selective or repair/enrichment media. In studies on enrichment of dairy environmental samples in University of Vermont medium and Listeria repair broth (UVM and LRB), combining these 2 primary enrichment media into a single tube of Fraser broth for dual secondary enrichment yielded a significantly higher percentage (p < 0.05) of Listeria-positive samples than did use of either LRB or UVM alone. Refinement of conventional Listeria recovery methods should consider the importance of the enrichment step, the nutritional needs of specific genetic types, and the physiological condition of Listeria isolates in foods.

Biological control of the Western flower thripsFrankliniella occidentalis in cucumber using the entomopathogenic fungusMetarhizium anisopliae

Biological control of the western flower thrips (WFT)Frankliniella occidentalis, using the entomopathogenicMetarhizium anisopliae-7 (M. a-7) strain was studied in three consecutive seasons under greenhouse conditions. Cucumber plants infested with WFT were sprayed with spore suspension of the fungusM. a-7 (0.5 g m-2), or the soil was treated with dry powder of the fungus (0.5 g m-2); the control was without fungus application. In the 1997 spring experiment, when the cucumber plants were initially infested with only three or four insects per leaf, the spore suspension spray caused a significant reduction in growth of the thrips population compared with the other treatments and the control. However, in the 1997 summer experiment, when the plants were initially heavily infested with WFT (10–15 insects per leaf), the spray treatment caused only a modest reduction in WFT population growth, and only after 4 weeks of treatment was the reduction significant. In the 1999 experiment, with a low initial WFT population of three or four insects per leaf, the spray treatment was effective in reducing the population growth to a lower level than in the other treatments or control. TheM. a-7 strain was found to be effective in reducing the population growth of WFT under greenhouse conditions, particularly when the initial thrips population was low to moderate.