Initial Egg Density Research Articles

Contest competition in Drosophila subobscura

AbstractThe role of larval intraspecific competition in laboratory populations of Drosophila subobscura was investigated. Mortality is density‐independent during the first 3 days after hatching but becomes density dependent as development proceeds to pupation. Although total biomass per patch was independent of initial egg density, competition between Drosophila larvae leads to the formation of smaller pupae. This resulted in a population that was dominated by suppressed individuals. Development rate of D. subobscura larvae was not affected by high larval densities. Smaller pupae give rise to females with fewer eggs in their ovarioles. A simple simulation model, predicting the effects of intraspecific competition on the fecundity of the next Drosophila generation is described.

Relative susceptibilities of eleven potato cultivars and breeders' clones toGlobodera pallida pathotype Pa 3, with a discussion of the interpretation of data from pot experiments

Curves according to the equationPf=M′ (1-e −aPi/M′ ) fitted well to the relations according to Seinhorst's (1993) modelPf=y e y h M(1-e −aPi/M ) between initial egg densities of potato cyst nematodes (Globodera rostochiensis, G. pallida)Pi up to 5T h (T h =the tolerance limit of haulm weight) andPf at the end of the growing season (a=maximum rate of reproduction,M, M′=different theoretical maximum egg densities). Variation of estimates ofM′, due to variation of the parameters of the submodelsy e andy h for the effect of weight reduction of haulms (and, therefore, of roots) on cyst production and damage to root tissue on egg production, respectively, was small enough to be ignored relative to experimental error. Therefore, ratios of values ofM′, determined in simultaneous pot experiments with different potato cultivars, are reliable measures of the relative host status of these cultivars at initial egg densitiesPi of these nematodes up to about 5T h . Variation between potato cultivars of growth reduction and damage to root tissue by the nematodes reduces the reliability of ratios of rates of relative susceptibility of these cultivars. The ratios between the maximum rates of reproduction ofG. pallida, pathotype Pa 3, on 8 out of 9 cultivars and one breeder's clone of potatoes and this rate on the susceptible cvs Bintje and Irene (relative susceptibilitiesrs a ) could be considered to be equal to the ratios of maximum population densitiesM′ on these cultivars (relative susceptibilitiesrs M′ ) (relative susceptibilities independent of initial egg density). The latter ratios were 0.59 times the first (relative susceptibilities negatively correlated with initial egg density) in one cultivar and one breeder's clone. Relative susceptibilitiesrs a andrs M′ of the tested cultivars and breeders clones suggest the existence of continuous ranges of both relative susceptibilities between 0.50 and 0.15 with, in a great majority of cases,rs a =rs M′ .

Field Population Dynamics of Soybean Cyst Nematode on Resistant and Susceptible Soybeans and Their Blends

Soybean cyst nematode (Heterodera glycines Ichinohe) (SCN) become an increasing problem in the upper midwest. In order to develop appropriate practices to manage SCN populations it is important to understand the population dynamics of SCN under field conditions. Soybean cyst nematode population dynamics were determined in naturally infested commercial soybean [Glycine max (L.) Merr.] fields in southern Minnesota on a monthly basis during 1991 and 1992 for an adapted susceptible (S) and a SCN Race 3 resistant (R) cultivar and three blends (25% R:75% S; 50% R:50% S; 75% R: 25% S). Population dynamics differed between sites and years. In 1991, fields with similar initial cyst densities were compared. Densities of second‐stage juveniles (J2) peaked in August at one site and gradually declined throughout the growing season at the other. Total cyst production was lower at the site where J2 densities declined. In 1992, fields with high and low initial egg densities were compared. SCN population densities increased when initial densities of J2 and eggs were low and decreased when initial J2 and egg densities were high. Physiological race of the nematode influenced population dynamics on resistant plants. The cyst index under field conditions for the resistant cultivar was 10 (moderately resistant) against Race and 32 (moderately susceptible) against Race 1. The blends generally lowered SCN population densities, but not significantly. Final egg density and cyst production for the resistant cultivar were significantly lower than the susceptible cultivar at each site. The use of SCN resistant cultivars alone or in a 75:25% mixture with a susceptible cultivar (25%) is recommended as a SCN population management strategy to delay shifts from one race to another thus prolonging the effectiveness of resistant cultivars.

Garden Herbs as Hosts for Southern Root-knot Nematode [Meloidogyne incognita (Kofoid & White) Chitwood, race 3

Twenty herb species were exposed to root-knot nematode under greenhouse conditions. The root systems were examined for root gall development and nematode reproduction as an indication of host suitability. The herbs evaluated were balm (Melissa officinalis L.), basil (Ocimum basilicum L.), catnip (Nepeta cataria L.), chamomile (Matricaria recutita L.), coriander (Coriandrum sativium L.), dill (Anethum graveolens L.), fennel (Foeniculum vulgare Mill.), hyssop (Hyssopus officinalis L.), lavender (Lavandula augustifolia Mill.), oregano (Origanum vulgare L.), peppermint (Mentha ×piperita L.), rocket-salad (Erurca vesicaria L.), rosemary (Rosmarinus officinalis L.), rue (Ruta graveolens L.), sage (Salvia officinalis L.), savory (Satureja hortensis L.), sweet marjoram (Origanum majorana L.), tansy (Tanacetum vulgare L.), thyme (Thymus vulgaris L.), and wormwood (Artemisia absinthium L.). Peppermint, oregano, and marjoram consistently were free of root galls after exposure to initial nematode populations of two or 15 eggs/cm3 of soil medium and were considered resistant. All other herb species developed root galls with accompanying egg masses, classifying them as susceptible or hypersusceptible to root-knot nematode. The highest initial nematode egg density (15 eggs/cm3) significantly decreased dry weights of 14 species. The dry weights of other species were unaffected at these infestation densities after 32- to 42-day exposure.

The regulation of numbers of cysts and eggs per cyst produced by Globodera rostochiensis and G. pallida on potato roots at different initial egg densities: correction and supplementary information

The regulation of numbers of cysts and eggs per cyst produced by Globodera rostochiensis and G. pallida on potato roots at different initial egg densities: correction and supplementary information

Modeling Growth and Survival in an Age-0 Fish Cohort

We applied an individual-based model to an age-0 cohort of smallmouth bass Micropterus dolomieu to simulate the cohortˈs growth and survivorship through its first growing season. The purpose was to determine whether the stock–recruitment characteristics of the age-0 fish could be predicted. The model smallmouth bass were exposed to size-dependent predation, size-independent mortality, and starvation mortality resulting from depletion of their prey supply. Survivorship curves were produced by model simulations. When survivorship at a given time was plotted against initial egg density during the early growing season, the curve resembled the peaked pattern of a Ricker-type curve. In contrast, curves for survivorship during the late growing season had no noticeable peak or maximum. Other results showed (1) strong density dependence of the mortality rate early in the growing season and density independence late in the growing season; (2) a distinct critical time (CT) during which the slope of the survivorship curve changed from a steep to a shallow decline, and (3) a decrease in CT as a function of the initial egg density. Competition for and overexploitation of prey during the early growing season produced these results. The model simulation results resembled patterns of some empirical data.

The Regulation of Numbers of Cysts and Eggs Per Cyst Produced By Globodera Rostochiensis and G. Pallida On Potato Roots At Different Initial Egg Densities

The relation between initial egg density Pi of Globodera rostochiensis pathotypes Ro 1 and Ro 3 and of G. pallida pathotype Pa 3 and the number of cysts producted per g dry haulm (considered to be proportional to size of the food source of the nematodes) Pf on various potato cultivars in ten pot experiments with ranges of initial egg densities was in accordance with the equation Pf = M(1 - e-x) with x = aPiM-1. This indicates a distribution of feeding sites of equal size for female juveniles in the roots according to Nicholson's competition model and adjustment of the population size in the roots by elimination of excess female juveniles by an active mechanism, thus preventing reduction of the size of the surviving females and their mortality by crowding, which would be an inefficient use of the food source. However, relative numbers of eggs per cyst y, were reduced according to the equation ye = me + (1 - me) 0.9z with z = PiT-1e-1 for Pi > Te and y = 1 for Pi < Te because of the adverse effect on the quality of the food source by invasion of the roots by much larger numbers of juveniles than could survive. Te varied between pathotypes, cultivars and experiments and was generally larger than T in the equation for the relation between Pi and final total plant weight. Therefore, the mechanism reducing the average number of eggs per cyst operates independently of that reducing plant size.

Enclosure Experiments on Survival and Growth of Black Drum Eggs and Larvae in Lower Chesapeake Bay

Experiments in 2.2 m3, in situ mesocosm enclosures indicate that black drum, Pogonias cromis, eggs and larvae potentially can survive in the lower Chesapeake Bay at ambient microzooplankton prey levels (≈200 prey 1−1) in the absence of predators. In growth experiments, larva mean growth rates to 10 d posthatch were similar (0.17 mm d−1 and 0.18 mm d−1) when fed at prey levels of 50 prey 1−1 and 200 prey 1−1. Individual growth rates, however, were more variable at 50 prey 1−1. Mortality rates also were comparable in 50 (27% d−1) and 200 (23% d−1) prey 1−1 enclosures. In a second experiment, the predation potentials of the hydromedusa Nemopsis bachei and the lobate ctenophore Mnemiopsis leidyi were estimated in relation to initial black drum egg prey density, presence of alternative <1 mm zooplankton prey, and estimated daily abundance of the jellyfish on the black drum spawning grounds. Mortality rates per medusa and ctenophore were similar (0.02–0.03 d−1), were not affected by presence of alternative prey, and were directly related to initial egg density. Results suggest that the gelatinous predators, especially the hydromedusa, could have cleared a high (≈38%) but variable fraction of the water column daily of fish eggs and yolk-sac larvae during the black drum spawning season. We hypothesize that the poor or episodic recruitment success of black drum in Chesapeake Bay results from a short spawning season that often coincides with abundance peaks of gelatinous predators and that predation on eggs and yolk-sac larvae may control recruitment.

The Relation Between Rate of Reproduction and Average Number of Eggs Per Cyst in Globodera Rostochiensis and G. Pallida

Pooled rates of reproduction of Globodera rostochiensis (five pathotypes) and of G. pallida (three pathotypes) from several pot experiments in four years on potato cv. Irene at initial population densities of 1 egg and 5 eggs/g soil were, per nematode species, proportional to average number of eggs per cyst and per pot and, per initial egg density, not correlated with number of cysts produced per egg in the inoculum. This also applied to rates of reproduction of pathotype Ro 1 on cvs Bintje and Mentor in four field experiments at initially 1 egg/g soil. The average number of cysts produced per egg in an inoculum of 5 eggs/g soil by G. rostochiensis in pots was 1.7 times that produced by G. pallida. At initially I egg/g soil the ratio was 1.5. Numbers of cysts of G. rostochiensis pathotype Ro 1 produced per egg in an inoculum of 5 eggs/g soil were proportional to dry haulm weight per pot. At initially 1 egg/g soil pathotype Ro 1 produced more cysts per egg in the inoculum than pathotype Ro 3 but not at initially 5 eggs/g soil. This indicates that the maximum cyst density per g dry haulms of the latter pathotype on cv. Irene was larger than that of the first. No differences between G. pallida pathotypes were apparent.

Hatching and Reproduction of the Potato Cyst Nematode, Globodera Rostochiensis, From Potato Fields in Western Australia as Influenced By Soil Temperature

The optimum hatching temperature for the Western Australian population of Globodera rostochiensis was 22°C in picrolonic acid with a maximum total hatch of 88 ± 6% after 42 days. In pots, under conditions simulating temperatures at the infestation sites, there were two peaks of hatching at 10-40 days and 110-140 days. Females and their eggs were first observed in the roots at 35 and 49 days respectively with most males in soil at 60 days. No second generation of eggs was observed following the second peak of juveniles in soil. Females on plants transferred from 15/10°C at 35 days after sowing developed between 5-30°C but the optimum temperature for egg development was 15°C. The relationship between initial and final egg density was as reported previously.

Growth and survival of bay anchovy Anchoa mitchilli larvae in mesocosm enclosures

Factors that affect sunrival and growth of bay anchovy Anchoa mitchilli larvae in the Chesapeake Bay, USA, were studied in situ in 3.2 m3 mesocosm enclosures. Experiments tested the effects of variable prey level and anchovy egg and larvae densities on growth and survival of larvae to at least 16 d post-hatching. Eggs were stocked at 100 m-3 with microzooplankton (< 150 ~m) prey added at nominal levels of 50, 500, 1500, or 5000 1-l. In a second series of experiments, eggs were stocked at 10, 100, or 2 1000 m-3 and prey level was maintained near 500 1-l. Larvae growth was rapid (0.39 to 0.63 mm d-l), even at the lowest prey levels and highest initial egg stocking densities. Growth rates tended to decrease as egg density increased. Instantaneous mortality rates were high (0.08 to 0.23 d-l) but lower than those reported for bay anchovy larvae from estuaries with gelatinous zooplankton and fish predators present. Highest mortality unexpectedly occurred in mesocosms with the highest prey level and lowest mortality occurred in enclosures with the highest initial egg stocking densities. Relative production decreased as prey level increased but Gw:Z ratios were above unity for all except the highest prey level experiment. In the stocking density experiments, highest production occurred in enclosures with the lowest initial egg densities. Some unexpected results may have been induced by effects of the mesocosm enclosures.

The initial density of avian eggs derived from the tables of Schönwetter

Two independent sources are presented which show that in spite of differences in relative yolk content, the density of egg content is virtually the same, namely, 1.031 g/cm3, SD=0.003, n=41. This constant allows one to calculate egg volume provided egg mass, shell thickness, shell mass, and surface area of the egg are known and to predict the initial egg density (egg mass/egg volume) using the surface area equation ofPaganelli et al. 1974. Measured initial egg densities reported in the literature for 53 species are compared with calculated values, using for each species the egg dimensions reported in Schonwetter's tables. The mean difference=−0.04 %, SD=0.8 %. Initial egg density values were calculated for all species listed inSchonwetter's Handbuch, and for extant, non-passerine birds ranged from 1.049 to 1.19 g/cm3 (n=3217). Density changes during incubation are discussed.

Natural Mortality of the Lesser Cornstalk Borer (Lepidoptera: Pyralidae) in a Peanut Agroecosystem

Lesser cornstalk borer (LCB), Elasmopalpus lignosellus (Zeller), populations were monitored for 3 yr in commercial peanut, Arachis hypogaea L., fields in an intensively cultivated area of Comanche County, Tex. Population census raw data were standardized to make LCB density estimates comparable among generations and years. Partial ecological life tables were constructed from standardized census estimates for five pivotal stages: eggs, just-hatched larvae, medium larvae, large larvae, and pupae. Mortality factors were classified as parasitism, disease, and unexplained. Identified mortality agents included an entomopoxvirus, a fungus, 13 primary parasites, and five predators. Survivorship curves implied a constant mortality rate with total generation mortality ranging from 87.1 to 96.5%. Keyfactor analysis revealed unexplained mortality was the major contributor to overall mortality, with unexplained mortality of large larvae the key mortality factor. Three methods of analyzing mortality–density relationships showed mortality was density independent, with initial egg density rather than mortality determining the resulting larval and pupal population densities.

FOLIAR APPLICATIONS OF BEAUVERIA BASSIANA (BALSAMO) VUILLEMIN FOR CONTROL OF THE COLORADO POTATO BEETLE, LEPTINOTARSA DECEMLINEATA (SAY) (COLEOPTERA: CHRYSOMELIDAE): AN OVERVIEW OF PILOT TEST RESULTS FROM THE NORTHERN UNITED STATES

AbstractAn overview of data from five research groups participating in a 3-year pilot test on the efficacy of foliar applications of Beauveria bassiana (Balsamo) Vuillemin for control of Colorado potato beetle, Leptinotarsa decemlineata (Say), populations in the northern United States is presented. Four treatments were used at each site: high and low B. bassiana dosages (5 × 1013 colony forming units (CFU) per hectare (ha) and 5 × 1012 CFU/ha), the recommended insecticide for each region, and an untreated check. The primary response variable was potato yield. For analyses considering test sites as replicates, during all 3 years the highest yields were produced in plots treated with insecticides. Within test sites, yields from plots receiving B. bassiana applications were greater than control plot yields in 8 of 24 trials but in only two of these instances, B. bassiana plot yields also did not differ from insecticide plot yields. Evaluating 1983 data from all states together, no differences were found between either high or low B. bassiana treatments and controls. The 1983 study design allowed no plot replication within states. In 1985, an altered plot design providing within-site replication demonstrated increased yield with increased dosage of B. bassiana when initial egg density was used as a covariate.Potato yields greater than control plot yields were noted with a minimum of 5.39 and 6.62 × 1011 CFU/ha B. bassiana. The lowest B. bassiana concentration producing yields not significantly different from insecticide plot yields was 6.62 × 1012 CFU/ha (Rhode Island, 1984). Defoliation ratings did not differ between B. bassiana treatments and controls in 1984 and 1985, although variability was found between yields.

Impact of the Egg Parasitoid, Anaphes sordidatus (Hymenoptera: Mymaridae), on the Carrot Weevil (Coleoptera: Curculionidae)

Objectives of the study were to evaluate impact of the egg parasitoid, Anaphes sordidatus (Girault), on its host, the carrot weevil, Listronotus oregonensis (LeConte), in the field. Mortality of carrot weevil larvae, in the absence of parasitism, was found to be density-dependent, with an average of 1–2 eggs surviving per carrot plant, regardless of initial egg density. Larval density averaged 1.5 per infested plant over the season. A. sordidatus adults emerged from 22.3% of eggs collected (maximum 49.3% on 1 August). There was no significant correlation between percentage of parasitism and egg density or plant growth characteristics. Since density-dependent mortality occurred in the absence of parasitism, the concept of effective parasitism (reduction in damage or larval survival) was developed to predict the overall effect of A. sordidatus on the carrot weevil.

Argentine stem weevil (Listronotus bonariensis) survival in the central North Island

Abstract Argentine stem weevil (Listronotus bonariensis (Kuschel)) populations in the central North Island were similar to Waikato populations and consisted of 2 complete generations per year, with negligible flight activity. There was a small spring and a larger summer generation. Populations had a higher overwintering survival, similar to that recorded in Canterbury. Overwintering survival was similar on several different ryegrass cultivars and over a wide range of host plant Acremonium endophyte infections. At the population densities often encountered on recently sown pastures in the Volcanic plateau, population survival (egg to adult) was not influenced by the proportion of ryegrass plants infected with Acremonium endophyte. The presence of endophyte deters adult weevils from ovipositing on infected ryegrasses but the presence of alternative hosts allows the population to develop. Population survival (egg to adult) was not associated with the ryegrass cultivar but was related to the initial egg density.

Numerical Changes and Population Regulation in Young Migratory Trout Salmo trutta in a Lake District Stream, 1966-83

(1) This 18-year study of numerical changes in a trout population is part of a general study on the population dynamics, growth and distribution of migratory trout, Salmo trutta L., in Black Brows Beck, a stony stream in the English Lake District. (2) Earliest and latest spawning dates were 3 November and 7 December; larger females spawned earlier than smaller females. Eggs per redd and mean egg weight increased with female size and decreased with time from the start of the spawning period. Migratory trout produced more and larger eggs per unit length of fish than did resident trout in a neighbouring stream. (3) In laboratory and stream experiments, 50% of eggs hatched and 50% of alevins emerged after 444? days and 852? days from fertilization, respectively. Egg weight positively affected alevin size at hatching and emergence from the gravel, but not development times. Survival times of newly-emerged fish kept in the laboratory without food were positively related to weight at emergence. (4) Population densities of eggs and alevins were very similar within but differed between year-classes (range: 12-133 eggs m-2). The dominant factor affecting population densities of young trout was the population density of eggs, and hence alevins, at the start of each year-class. Alevin emergence time, weight of eggs or alevins, water temperature, numbers of older trout and numbers of other fish species (chiefly Cottus gobio L.) had no obvious effect. The number of recruits to each year-class was related to the initial egg density by the Ricker, dome-shaped, stock-recruitment curve. Maximum recruitment was estimated as 7.2 fish m-2 (95% CL = 6.5-8.0) soon after the fry stage ended in May/early June and 2*0 (? 0-5) fish m-2 in late August/September. Optimum egg densities for these values were estimated as 40.0 m-2 (95% CL = 38.5-41-7) and 62.5 m-2 (55.6-71-4) respectively. (5) Mortality was very low for eggs and alevins but high for young trout trying to establish feeding territories. The instantaneous mortality rate was linearly related to egg density and hence was density-dependent. The mortality rate for June to August was also negatively related to, and appeared to compensate for, the high mortality rate in May/early June.

Population studies on pea cyst‐nematode Heterodera goettingiana Liebs.

SUMMARYChanges in populations of Heterodera goettingiana Liebs. were studied in microplots containing three kinds of soil. Starting with an artificially uniform population, varieties of pea which matured quickly induced smaller numbers of cysts and eggs than later‐maturing varieties although there was ample time for completion of the life cycle on the former. Field bean was comparable with the late‐, and broad bean with the early‐maturing pea varieties.When one variety of pea was grown on all plots of a group, yield decreased in proportion to the density of the population before planting. The relationship between yield and initial population over a narrow population range was expressed equally well by the simple equations Y=a+bx or Y=a+blogx, where Y= yield, x= the number of eggs, a= the Y intercept and b the regression coefficient. For plots with a wide range of initial populations (4–359 eggs/g. soil), neither equation was adequate and the relationship was best fitted by a sigmoid curve.In two sets of plots, the influence of two population levels, nitrogen versus no nitrogen, and light versus heavy soil, was tested. Soils and populations affected yield significantly; nitrogen was ineffective on light soil but increased yield on the heavy soil. Only soil type affected the final population, that in the heavy soil which gave the greater yield being twice as large.When peas were grown, the final population rose to a ceiling level independent of the initial population size. In the plots with widest initial population range, the ceiling level was determined by the number of females (new cysts) formed. Their number was almost constant over the whole initial population range and they produced on average 129 eggs/cyst which was the maximum theoretically possible rate of increase under the conditions of the experiment. At small initial egg densities (4 eggs/g.) about 50% of the eggs became female and at great densities (359 eggs/g.) only 1% or less.Final populations in the microplots bore no relationship to yield of peas. It is suggested that the size and form of the central part of the root system determines how many females the roots can support and that root size is one of the factors that determines ceiling levels.Nematicides used to decrease numbers of cyst‐nematode eggs or larvae in soil tend to remove only those surplus to the carrying capacity of root systems. Nematicides or enemies able to kill established females before they produce eggs would control reproduction more effectively.

A Population Experiment With Heterodera Goettingiana Lieb. and a Relatively Inefficient Host, Broad Bean

Broad beans (Vicia faba L.) grown in garden plots gave a negative linear regression for yield on the logarithm of the initial egg density of pea root eelworm (Heterodera goettingiana Lieb.). It was confirmed that broad beans can only support a low population of this eelworm. It is suggested that maximum production of new eggs occurred at an intermediate initial egg density, with few new eggs above an initial density of 400 eggs/g.

The Effects of Red Beet and of Hesperis Matronalis L. On a Population of Heterodera Schachtii Schm

The effect on a population of beet eelworm of growing Hesperis matronalis was tested in microplots in 1956. For comparison, two other treatments were used: fallow, and red beet. Linear regressions of final on initial eelworm densities were made, with modification of the usual analysis to allow for the errors of measurement in the initial population. The rate of decay for eggs with H. matronalis increased with higher initial egg density, but was never sufficiently greater than the rate with fallow to be worthwhile for controlling infestations of beet eelworm. Red beet acted as a trap-crop in this year; few if any new cysts were formed, and the rate of decay was similar to that of H. matronalis.