Initial Population Density Research Articles

Pathogenicity and Host-Parasite Relationships of Meloidogyne arenaria in Sweet Basil.

Stunted growth of sweet basil (cv. Genovese) associated with large patches and severe soil infestations by the root-knot nematode Meloidogyne arenaria race 2 were observed in open fields at the end of the crop-growing season in Albenga, province of Savona, Northern Italy by early September 2007. Observed morphological traits of nematode life stages and results of analysis of isozyme electrophoretic patterns and differential host tests were used for nematode species and race identification. Nematode-induced mature galls (either in naturally infected plants or in artificially inoculated root tissues) were spherical or ellipsoidal and confluent along the root axis, containing usually several females, males, and egg-masses with eggs. Feeding sites were characterized by the development of giant cells that contained several hypertrophied nuclei and nucleoli. Giant cell cytoplasm was aggregated along the thickened cell walls. Vascular elements within galls appeared disorganized and disrupted. Due to the heavy damage observed, the relationships between the initial population density and growth of basil plants was also tested in a greenhouse experiment in which inoculum levels varied from 0 to 512 eggs and juveniles/cm3 of soil. Height and top fresh weight data of the inoculated and control plants was fitted to Seinhorst's model. Tolerance limits with respect to plant height and fresh top weight of basil cv. Genovese plants to M. arenaria race 2 were estimated as 0.15 eggs and juveniles/cm3 of soil. The minimum relative values (m) for plant height and top fresh weight were 0.39 and 0.19 at initial nematode population density (Pi) ≥16 eggs and juveniles/cm3 of soil, respectively. The maximum nematode reproduction rate (Pf/Pi) was 448.7 times at an initial population density of 4 eggs and second-stage juveniles/cm3 of soil.

Response of Old and New Soybean Cultivars to Heterodera glycines Ichinohe

Soybean [Glycine max (L.) Merr.] cyst nematode (Heterodera glycines Ichinohe; SCN) causes significant yield loss each year. New cultivars (released since 1997) have superior yield compared with older cultivars (released between 1938 and 1983), but responses to SCN have not been evaluated. Studies were established at three locations in Iowa for 2 yr to measure yield loss of 23 cultivars that differed in year of release and SCN resistance in locations with varying SCN population density and Heterodera glycines Type (HG Type). Initial SCN population densities (Pi) were <1000 eggs 100 cm−3 (HG Type 2.7) at Whiting, between 1000 and 4000 eggs 100 cm−3 (HG Type 1.2.5.7 and 2.5.7) at Nevada, and between 4000 and 12,500 eggs 100 cm−3 (HG Type 0 and 7) at De Witt in 2005 and 2006. Analysis of simple effects from year × location interactions consistently showed that new SCN‐resistant cultivars had lower final SCN population densities (Pf) and reproduction factors (Rf) compared with old and new SCN‐susceptible cultivars. Among all locations, seed yield of new SCN‐resistant cultivars was 14% greater than new SCN‐susceptible cultivars and 32% greater than old SCN‐susceptible cultivars. Yield increase was a result of increased seed production (seeds m−2) and not from a change in seed mass. Yield of new SCN‐susceptible cultivars was 18% greater than old SCN‐susceptible cultivars but did not provide greater control of SCN. These data indicate that yield increases with new SCN‐susceptible cultivars are not the result of improved SCN management. Data support the selection of SCN‐resistant cultivars for fields in which SCN has been identified, regardless of Pi or HG Type to increase yield and reduce SCN population densities.

오이 시설재배시 고구마뿌리혹선충의 경제적피해한계

고구마 뿌리혹선충(Meloidogyne incognita)의 시설재배 오이에 대한 경제적 피해한계를 조사하기 위하여 비닐하우스 내에 합판으로 만든 박스(<TEX>$30{\times}40{\times}15cm$</TEX>)를 묻고 박스 내 토양 <TEX>$100cm^3$</TEX>당 뿌리혹선충 유충의 밀도를 0, 10, 30, 100, 300, 600마리로 조정된 토양을 넣었다. 각 박스에는 '장수신토좌'에 접붙인 '슈퍼만촌'오이 23일 묘를 8월 1일 1포기씩 심고 11월까지 각 구당 오이 수확량을 조사하였다. 뿌리혹선충의 유충밀도와 수량과의 회귀식은 <TEX>$Y=0.82-0.04{\cdot}Log_{10}$</TEX>(Pi+1)로 방제 비용을 감안한 경제적 피해 허용 수준은 정식전 뿌리혹선충 유충의 밀도가 토양 <TEX>$1,000cm^3$</TEX>당 5마리이면 살선충제 입제 살포가 경제적이고, 유충의 밀도가 토양 <TEX>$1,000cm^3$</TEX>당 25마리 이상이면 훈증제를 처리하는 것도 고려해 볼 수 있다. 오이 시설재배시 뿌리혹선충의 피해를 방지하기 위해서는 최소한 정식 수개월 전에 미리 토양 선충 밀도를 조사해야 할 것이다. To determine the economic threshold level of Meloidogyne incognita on cucumber in greenhouse conditions, cucumber seedlings(Cucumis sativa L. cv. 'Super Manchon') grafted on 'Jangsushintozoa'(Cucurbita maxima x Cu. moschata) were planted in wooden boxes(<TEX>$30{\times}40{\times}15cm,\;L{\times}W{\times}D$</TEX>) under a plastic house in August 01 and harvested from Sep. 01-Oct. 30, 2006. The initial nematode population densities(Pi) in the wooden boxes were adjusted to 0, 10, 30, 100, 300, and 600 second-stage juveniles(J2)/100 <TEX>$cm^3$</TEX> soil. The relationship of total fruit yield to Pi level could be adequately described by a linear regression equation, <TEX>$Y=0.82-0.04{\cdot}Log_{10}$</TEX>(Pi+1). Initial nematode densities(Pi) before planting in excess of 5 J2/1,000 <TEX>$cm^3$</TEX> soil caused in total yields loss that is equivalent to the costs of granular nematicide application; Pi level in excess of 25 J2/1,000 <TEX>$cm^3$</TEX> soil caused in total yields loss that exceed the costs for application of fumigants at current control costs. We propose two different management strategies depending on nematode densities, (i) application of non-fumigant granular nematicides for M. incognita Pi level of 5 J2/1,000 <TEX>$cm^3$</TEX> soil and (ii) fumigant treatment with Pi level over 25 J2/1,000 <TEX>$cm^3$</TEX> soil. Soil samples to determine population density of Meloidogyne spp. for advisory purposes should be taken several months before planting time, which allows a period of time enough for implementing management procedures.

Purple Deadnettle (Lamium Purpureum) Emergence and Removal Time Effects on Soybean Cyst Nematode (Heterodera Glycines)

Abstract Purple deadnettle is an obligate winter annual weed and an alternate host of soybean cyst nematode (SCN). Field experiments were conducted using microplots to determine (1) the effect of purple deadnettle planting date and (2) the effect of purple deadnettle removal time on SCN egg population density in continuous no-tillage soybean. A population change factor (PCF) to assess treatment effects on SCN population densities was calculated by dividing the SCN population density at each sampling time (Pf) by the initial population density before treatments were applied (Pi). In the planting date experiment, purple deadnettle seeded on October 3, 11, and 18 resulted in PCF values ranging from 7.28 to 11.41, which were three- to fivefold higher than the PCF values for the weed-free control or purple deadnettle seeded on September 6, 20, and 27. Self-thinning of purple deadnettle seeded in September may have resulted in higher levels of SCN mortality compared to later seeding dates. In the removal time e...

Population extinction and survival in a hostile environment

We study the conditions for extinction and survival of populations living in a patch surrounded by a hostile environment. We find analytic expressions for the steady states when population dynamics is described by diffusion and reaction is driven by compensation, depensation, or critical depensation growths. The role of initial population density is studied, and the complete bifurcation diagrams are constructed and validated numerically for the three cases studied.

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.

Soil Population of Helicotylenchus multicinctus under Pueraria phaseoloides, Flemingia macrophylla and Natural Bush Fallows and their Effect on Plantain Yield in the Humid Forest Zone of Southern Cameroon

ABSTRACT Soil population densities of Helicotylenchus multicinctus (Cobb) Golden were assessed under Flemingia macrophylla [(Willd.) Merrill] and Pueraria phaseoloides (Roxb.) Benth, and natural bush fallows over 24 months in three villages in southern Cameroon. Also assessed was the effect of H. multicinctus on yield of plantain. Trials were set up in four to five year-old Chromolaena odorata (L.) R. M. King & H. Rob. dominated natural bush fallow. Initial H. multicinctus population density at Ngoumou (512 100 cm−3 soil) was (p < 0.05) higher than at Mfou (241 100 cm−3 soil) and Nkometou (70 100 cm−3 soil). H. multicinctus population was correlated with (i) total annual rainfall (r = 0.79; p = 0.01) and (ii) clay content (r = 0.95; p < 0.001). At 12 months after planting (MAP), P. phaseoloides and F. macrophylla supported (p < 0.01) lower population densities of H. multicinctus (88 and 152 100 cm−3 soil, respectively) compared with the natural regrowth (287 100 cm−3 soil). Comparing the initial population with that at 12 MAP for each of the three fallow systems, both P. phaseoloides and F. macrophylla reduced density of H. multicinctus (p < 0.05). However, when the initial population density was compared with that at 24 MAP only under P. phaseoloides was the reduction maintained. Contrarily, population density under F. macrophylla was comparable between the initial and 24 MAP. This is the first report of the nematode reducing effect of P. phaseoloides. Plantain flowering and subsequent harvesting was earliest under P. phaseoloides, different from that under F. macrophylla (p < 0.05). Plant bunch weight was positively correlated with the length of the fruit filling period (r = 0.67) which in turn was positively correlated with the non damaged root index (NDRI) (r = 0.58). Plantain under P. phaseoloides had the highest NDRI and consequently recorded the greatest yield (p < 0.05). There was no difference in plantain yield between the natural regrowth and F. macrophylla. Pueraria phaseoloides could be used as one component for the biological control of H. multicinctus.

Suppression of root-knot nematode damage to succeeding sweet potato by summer-sown cultivation of an oat variety, "Tachiibuki"

Reproduction of four populations of Meloidogyne incognita on ten oat varieties was examined in a greenhouse. Eggmass numbers produced on oat roots inoculated with 500 J2 were counted. Eggmasses of all nematode populations were present on all oat varieties but“Tachiibuki”had the lowest number (1.8 - 11.8 eggmasses / root system). Summersown cultivation of four early forage oat varieties sown in September and a fallow treatment were examined in a field infested with M. incognita and M. arenaria. The final / initial population density of J2 (Pf / Pi) in December for varieties “Haeibuki”,“Super Hayate Hayabusa”, “Tachiakane”,“Tachiibuki”and the fallow were 36.5, 34.7, 23.9, 1.9 and 0.2, respectively. Yield of succeeding sweet potato planted in May of the next year and harvested in September was highest in the plot that was previously cropped with the variety “Tachiibuki”, and in the “Tachiakane” plot which also received a nematicide treatment (1.5% a.i. fosthiazate, 20 kg / 10 a) before planting. Sweet potato storage roots from the “Haeibuki”, “Super Hayate Hayabusa” and fallow plots were significantly damaged by root-knot nematode with similar low yields. Damage to storage roots caused by the nematode was significantly reduced by the preceding “Tachiibuki” cropping to an extent similar to the nematicide treatment.

Competition between the Rotifer Brachionus calyciflorus and the Cladoceran Moina macrocopa in Relation to Algal Food Concentration and Initial Rotifer Population Density

ABSTRACT The rotifer Brachionus calyciflorus occurs simultaneously with the cladoceran Moina macrocopa in tropical water bodies, and mass cultures of M. macrocopa are sometimes contaminated with B. calyciflorus. The effects of algal food concentration (Chlorella vulgaris) and initial rotifer population density on the competition between B. calyciflorus and M. macrocopa were tested using population growth experiments, and the influence of adult M. macrocopa on the instantaneous reproductive rates, egg ratios, and survivorship of B. calyciflorus females was investigated in short-term experiments. M. macrocopa rapidly excluded B. calyciflorus from mixed-species cultures but was itself unaffected by the presence of the rotifers, regardless of the algal food concentration or initial rotifer population density. Adult M. macrocopa imposed significant negative effects on the instantaneous reproductive rates, egg ratios, and survivorship of newborn individuals of B. calyciflorus. The magnitude of effects imposed by M. macrocopa increased with decreased food level and increasing density of adult M. macrocopa.

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 &lt;I&gt;Ephestia kuehniella&lt;/I&gt; and &lt;I&gt;Plodia interpunctella&lt;/I&gt; (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.

No effect of body condition at weaning on survival and reproduction in prairie voles

The physiological state of an animal may have a significant impact on its reproductive success because individuals in good body condition are generally considered to be competitively superior to individuals in poor body condition. In this study, we tested if body condition at weaning affected survival and reproduction of prairie voles ( Microtus ochrogaster (Wagner, 1842)) living under ecologically relevant conditions at two different initial population densities. We detected no evidence that better body condition at weaning was associated with either enhanced survival or reproduction. Moreover, genetic analysis of parentage found that mating between males and females was random with respect to body condition. Results of this study indicate body condition at weaning was not a reliable predictor of future survival or reproduction in prairie voles. This may be because body condition at weaning does not accurately forecast the energetic state of prairie voles at later ages, or because other factors have a greater effect on an individual’s survival and reproductive success at the densities observed in this study.

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.

Density-Dependent Response of the Pea Aphid (Hemiptera: Aphididae) to Imidacloprid

A study was conducted to determine the influence of initial population density on the effects of pesticides on pea aphid, Acyrthosiphon pisum (Harris), populations. Three initial starting densities of pea aphids (147, 295 and 590 aphids per m2) were exposed to no pesticide or imidacloprid at rates of 1 or 5 g ai/ha on broad bean plants, Vicia faba L., in a greenhouse. Ten days later, population size was assessed. In general, higher initial aphid population density resulted in a higher final population density for all imidacloprid concentrations. However, population growth rates for populations started with the highest density (590 aphids per m2) were significantly lower than those with initial densities of 147 and 295 aphids per m2. This was due to a relative reduction in population number. Populations begun with 147 aphids per m2 were 50% lower after exposure to the highest concentration of imidacloprid, whereas the populations begun with 295 and 590 aphids per m2 were 42 and 25% of the starting population size, respectively. Therefore, the pesticide actually had a greater impact on the population started with the highest density. This can be explained by a synergistic effect of the pesticide and crowding. The lower growth rate observed in the population started with the highest density was probably due to crowding, whereby aphids approached the carrying capacity and were stressed. Even though these populations were reduced, final density was still sufficiently high to limit resources. These results indicate that the response of organisms to stress is influenced by population density at the start of a stressful event, such as a pesticide exposure. Therefore, different experimental designs may result in different outcomes and starting population densities must be carefully considered when designing population-level toxicological experiments.

Modification of the data-processing method for the turbidimetric bioassay of nisin

The data processing method of the turbidimetric bioassay of nisin was modified to facilitate its industrial application. The influence of the initial indicator concentration was minimized by a redefined specific dose of the bacteriocin as the quotient between the titer of the added bacteriocin and the initial population density of the indicator in the suspension. It was found that dc = 0.125 microg ml(-1) was the critical dose of nisin that can cause a complete inhibition of the indicator, Pediococcus acidilactici UL5, with an initial OD of 0.135. To eliminate the interference of the cell debris, an equation, epsilonI = ODi(1-di)/OD0 = epsilonA(1-di/dc), exploiting dc, was formulated to obtain the intrinsic survival proportion. The use of the specific dose of the bacteriocin and the intrinsic survival proportion as parameters of the dose/response curve greatly enhanced its repeatability and feasibility. A dual-dosage approach was developed to further simplify the conventional standard dose/response curve method.

Effects of Cover Cropping, Solarization, and Soil Fumigation on Nematode Communities

Impacts of sustainable soil-borne pest management strategies on the soil ecosystem were compared to that of methyl bromide fumigation using nematode community analysis. A field experiment was conducted in 2003 and repeated in 2004. Soil treatments carried out in summer months included methyl bromide (MB) fumigation, solarization (S) for 6 weeks, cowpea (Vigna unguiculata) cover cropping for 3 months (CP), combination of solarization and cowpea cover cropping (S + CP), and a weedy fallow throughout the summer used as a control (C). All treated plots were planted to pepper (Capsicum annuum) after the application of the treatments at the end of the summer. In general, responses of nematode communities to soil treatments were more obvious at pepper planting than at 4 months after planting. In 2003, initial population densities of bacterivores and fungivores at pepper planting followed a hypothesized pattern of MB > S > S + CP > CP > C. However, this perturbation did not persist after a cycle of vigorous growth of a pepper crop. Omnivorous nematodes were the most sensitive nematode trophic group, with impact from soil treatment lasting until the end of the pepper crop. Nematode community indices such as ratio of fungivores to fungivores plus bacterivores, richness, and structure index were especially useful in detecting impacts by the various soil treatments. While disturbance from MB on the nematode communities lasted at least until the end of the pepper crop, that from the solarization often reduced or disappeared at the end of the experiment. The CP treatment enhanced many of the beneficial nematodes but failed to suppress the final population densities of herbivorous nematodes at pepper harvest (Pf). However, CP + S consistently reduced the Pf of herbivores to levels equivalent to MB in both years, whereas, this level of suppression could not be achieved by either CP or solarization alone.

Seasonality and Adult Habitat Use by FourDiabroticaSpecies at Prairie-Corn Interfaces

Although Diabrotica pest species have been well studied in field corn, Zea mays L., relatively little is known about adult habitat use by pest and nonpest species at prairie-corn interfaces. Therefore, the objective of this work was to compare seasonal patterns of beetles of four Diabrotica species and their use of remnant prairie and adjacent field corn habitats in southeastern Nebraska. The study was conducted at five sites in 2001 and continued at three sites in 2002. The Diabrotica species included D. barberi Smith and Lawrence, D. cristata (Harris), D. virgifera virgifera LeConte, and D. undecimpunctata howardi Barber. Cucurbitacin vial traps were used to monitor Diabrotica populations. Available flowers and Diabrotica use of these flowers were also documented. The virgifera group species (D. barberi, D. cristata, and D. v. virgifera) were closely tied to a primary habitat, corn or prairie, but moved to secondary habitat if relative attractiveness of food sources in the primary habitat decreased; these three species had high initial population densities that decreased over the season. The one fucata group species (D. u. howardi) was found in various habitats, with low initial densities that increased over the season. Habitat type and contrasts in plant phenology seem to be key factors that influenced habitat choice by Diabrotica species; this especially affected the level of noncorn habitat use by pest species D. v. virgifera and D. barberi. Use of crop and noncrop parts of the agroecosystem by pest species suggests that a more holistic approach rather than a single field view may be appropriate when managing corn rootworms.

The effect of the Holling type II functional response on apparent competition

This article analyzes the classical 2-resource–1-consumer apparent competition community module with the Holling type II functional response. Two types of resource regulation (top-down vs. combined top-down and bottom-up) and two types of consumer behaviors (inflexible consumers with fixed preferences for resources vs. adaptive consumers) are considered. When resources grow exponentially and consumers are inflexible foragers, one resource is always outcompeted due to strong apparent competition. Density dependent resource growth relaxes apparent competition so that resources can coexist. As multiple attractors (either equilibria or limit cycles) coexist, population dynamics and community composition depend on initial population densities. Population dynamics change dramatically when consumers forage adaptively. In this case, the results both for top-down, and combined top-down and bottom-up regulation are similar and they show that species persistence occurs for a much larger set of parameter values when compared with inflexible consumers. Moreover, population dynamics will be chaotic when resource carrying capacities are high enough. This shows that adaptive consumer switching can destabilize population dynamics.

Maximum value of the pulse energy of a passively Q-switched laser as a function of the pump power

The finite recovery time Ts of the bleached absorber is presented as one of the possible mechanisms accounting for the increase-maximum-decrease in pulse energy E with the pumping rate Wp in cw-pumped passively Q-switched solid-state lasers, by analytically evaluating the sign of the derivative partial differentialE/ partial differentialWP. The results show that, in the low pump regime (T>Ts, T is the interpulse period), the initial population density ni remains constant, the final population density nf decreases with Wp, and this results in a monotonic increase of E with Wp. In the high pump regime (T<Ts), ni decreases but nf remains the same with Wp; this results in a monotonic decrease of E with Wp. At the critical region (T approximately Ts), E reaches its maximum value. A cw-pumped Yb:YAG laser passively Q switched by a Cr4+:YAG absorber is demonstrated to confirm this model. The theoretical model is also applied to the analysis of three previously reported passive Q switching solid-state [Nd:GdVO4, Nd+:LaSc3(BO3)4 (Nd+:LSB), and Nd:YAG] lasers experiments.

Time Delay and Initial Population Density Affect Interactions Between &lt;I&gt;Encarsia pergandiella&lt;/I&gt; Howard and &lt;I&gt;Eretmocerus mundus&lt;/I&gt; Mercet (Hymenoptera: Aphelinidae)

Differences in dispersal abilities between parasitoid species sharing a host may result in asynchronous colonization of host patches and periods of time (delays) when hosts are exploited in the absence of potential competitors. Previous field cage studies showed Eretmocerus mundus Mercet and Encarsia pergandiella Howard were able to coexist for the duration of a field season when released simultaneously and at the same rate on whitefly-infested cotton plants, and interspecific competition did not influence their ability to suppress their host. The objectives of this study were to investigate the effects of time delay and initial population density on the population dynamics of En. pergandiella and Er. mundus and their abilities to suppress Bemisia argentifolii Bellows and Perring. Field cages enclosing cotton plants were inoculated with whitefly adults and treated by releasing Er. mundus and En. pergandiella either in sequence (one before the other), at two release rates (1× or 3×), and both in sequence and at two release rates. The sequence of release alone did not affect parasitoid population dynamics. However, when released at two rates, or in sequence and at two rates, the density of En. pergandiella was higher at the high rate and when released first. Results suggest that early colonization of host patches is favorable to En. pergandiella without a negative impact on host suppression. Results provide insight to explain the observed patterns of establishment and population dynamics of Aphelinid parasitoids assemblages in agroecosystems.