An analysis of the population dynamics of the Jamaican sugar-cane pest Saccharosydne saccharivora (Westw.) (Hom., Delphacidae)

1972 ◽  
Vol 62 (1) ◽  
pp. 73-85 ◽  
Author(s):  
J. R Metcalfe
Keyword(s):  
Population Dynamics ◽  
Selective Breeding ◽  
Population Analysis ◽  
Graphical Analysis ◽  
Leaf Nitrogen ◽  
Mortality Factor ◽  
Agricultural Practice ◽  
Mortality Factors ◽  
Density Dependent ◽  
Key Factor

The Varley & Gradwell method of population analysis is applied to data on populations of Saccharosydne saccharivora (Westw.), comprising 51 generations from 21 fields, obtained in Jamaica in 1961–62. Populations were estimated at five points in each generation, namely, maximum potential natality, and numbers of eggs laid, instar 1, peak instars 3–5, and of normal reproducing adults. Taking maximum potential natality as the first point in each life budget, graphical analysis showed that the key factor was mortality between instar 1 and reproducing adults or between peak instars 3–5 and reproducing adults. Reduced fecundity, due to submaximal leaf nitrogen, was density independent or possibly inversely density dependent; one egg parasite, Tetrastichus sp., was inversely density dependent while another, Anagrus flaveolus Waterh., and an undetermined egg mortality factor were density independent; parasitism of nymphs and presumably adults also by Stenocranophilus quadratus Pierce was density dependent, and was Considered to be the only regulating factor. The key factor was density independent, and it is concluded that, of the separate mortality factors contained within it, dispersal of adults is the most important. This itself depends on crop characters which could be altered by selective breeding or agricultural practice.

scholarly journals A generic population model for the African tick Rhipicephalus appendiculatus

Parasitology ◽  
1997 ◽  
Vol 115 (3) ◽  
pp. 265-279 ◽  
Author(s):  
S. E. RANDOLPH ◽  
D. J. ROGERS
Keyword(s):  
South Africa ◽  
Population Model ◽  
Egg Production ◽  
Population Analysis ◽  
Rhipicephalus Appendiculatus ◽  
Mortality Factors ◽  
Density Dependent ◽  
Tick Abundance ◽  
Annual Range ◽  
Parameter Values

We present a simulation population model for the African tick Rhipicephalus appendiculatus, based on previous analyses of the mortality factors most closely correlated with observed population changes at 11 sites in equatorial and South Africa. The model incorporates temperature-dependent rates of egg production and development, climate-driven density-independent mortality rates, particularly during the adult-larval stage, and density-dependent regulation of both nymphs and adults. Diapause is also included for tick populations in southern Africa. The model successfully describes both the seasonality and annual range of variation in numbers of each tick stage observed at each of 4 test sites in Uganda, Burundi and South Africa. Sensitivity analysis showed that the final version of the model is robust to 4-fold variation in most parameter values (that were per force based on informed guesses), but is more sensitive to the regression coefficients determining density-dependent interstadial mortality (that were derived from analysis of field data). The model is able to predict the seasonality of ticks from a site in Kenya where a full prior population analysis was not possible because only adults and nymphs had been counted. The model is potentially applicable to other species of ticks, both tropical and temperate, to predict tick abundance and seasonality as risk factors for tick-borne diseases.

scholarly journals Population dynamics of Saissetia oleae. II. Life-tables and key-factor analysis

2017 ◽  
Vol 8 ◽  
pp. 59 ◽  
Author(s):  
E. T. Kapatos ◽  
E.T. Stratopoulou
Keyword(s):  
Factor Analysis ◽  
Population Dynamics ◽  
Population Change ◽  
Life Tables ◽  
Population Fluctuations ◽  
Mortality Factors ◽  
Population System ◽  
Key Factor ◽  
Key Factor Analysis ◽  
Table Data

A series of life-tables for the population of Saisselia oleae (Oliv.) (Homoptera: Coccidae) during five yearly generations (1981-86) were constructed in Corfu. Key-factor analysis carried out on the life-table data indicated that mortality of young stages during summer, caused mainly by the high temperatures, and mortality during spring, caused mainly by predation, determine total population change within each generation. These two mortality factors are the predominant factors of the population dynamics of S. oleae determining population fluctuations. The other mortality factors of the population system of S. oleae were less important. Summer parasites and egg predators, in particular, do not play any significant role on the population dynamics of S. oleae.

Major Factors in Survival of the Immature Stages of Pieris rapae (L.)

1966 ◽  
Vol 98 (6) ◽  
pp. 653-662 ◽  
Author(s):  
D. G. Harcourt
Keyword(s):  
Population Dynamics ◽  
Survival Rate ◽  
Pieris Rapae ◽  
Pupal Stage ◽  
Population Data ◽  
Life Tables ◽  
Immature Stages ◽  
Mortality Factors ◽  
Key Factor ◽  
Major Factors

AbstractDetailed studies on the population dynamics of the imported cabbageworm, Pieris rapae (L.), have been carried out at Merivale, Ontario, since 1959. A method for preparing life tables is described and a mean life table is presented for 18 generations of the species on cabbage. Population data for the preadult period show that there are three age intervals during which extensive mortality may occur: (1) between hatching and the second moult, (2) instars three to five, and (3) during the pupal stage. The analysis of successive age-interval survivals in relation to generation survival showed that the latter is largely determined by the survival rate for (2). Examination of the life tables revealed that a granulosis of the larvae caused by a capsule virus is the key factor in generation survival. Major mortality factors include rainfall and parasites.

scholarly journals Whitefly population dynamics in okra plantations

2005 ◽  
Vol 40 (1) ◽  
pp. 19-25 ◽  
Author(s):  
Germano Leão Demolin Leite ◽  
Marcelo Picanço ◽  
Gulab Newandram Jham ◽  
Márcio Dionízio Moreira
Keyword(s):  
Population Dynamics ◽  
Visual Inspection ◽  
Leaf Nitrogen ◽  
Trichome Density ◽  
Mortality Factors ◽  
Total Rainfall ◽  
Bottom Part ◽  
Lack Of Information ◽  
Insect Migration ◽  
Biotype B

The control of whitefly Bemisia tabaci (Gennadius) biotype B (Hemiptera: Aleyrodidae) on okra (Abelmoschus esculentus L.) consists primarily in the use of insecticides, due to the lack of information on other mortality factors. The objective of this study was to evaluate the spatial and temporal population dynamics of the whitefly B. tabaci biotype B on two successive A. esculentus var. "Santa Cruz" plantations. Leaf chemical composition, leaf nitrogen and potassium contents, trichome density, canopy height, plant age, predators, parasitoids, total rainfall and median temperature were evaluated and their relationships with whitefly on okra were determined. Monthly number estimates of whitefly adults, nymphs (visual inspection) and eggs (magnifying lens) occurred on bottom, middle and apical parts of 30 plants/plantation (one leaf/plant). Plants senescence and natural enemies, mainly Encarsia sp., Chrysoperla spp. and Coccinellidae, were some of the factors that most contributed to whitefly reduction. The second okra plantation, 50 m apart from the first, was strongly attacked by whitefly, probably because of the insect migration from the first to the second plantation. No significant effects of the plant canopy on whitefly eggs and adults distribution were found. A higher number of whitefly nymphs was found on the medium part than on the bottom part.

POPULATION DYNAMICS OF LEPTINOTARSA DECEMLINEATA (SAY) IN EASTERN ONTARIO: III. MAJOR POPULATION PROCESSES

1971 ◽  
Vol 103 (7) ◽  
pp. 1049-1061 ◽  
Author(s):  
D. G. Harcourt
Keyword(s):  
Population Dynamics ◽  
Leptinotarsa Decemlineata ◽  
Food Resource ◽  
Weather Conditions ◽  
Density Dependent ◽  
Natural Agents ◽  
Potato Beetle ◽  
Key Factor ◽  
Leptinotarsa Decemlineata Say ◽  
Population Processes

AbstractAn appraisal of population processes in the Colorado potato beetle, Leptinotarsa decemlineata (Say), on its principal host plant showed that the insect has no natural agents that act in a manner that prevent it from overshooting its food supply. It is little affected by weather conditions or predators, and its only parasite, the tachinid Doryphorophaga doryphorae (Riley), is inversely density dependent in its action. Once the beetle has exploited its food resource, the larvae starve and the adults emigrate in quest of other hosts.The analysis of age interval survivals showed that populations are both regulated and disturbed by the principal key factor, adult migration, which is density dependent but overcompensating. A predictive model based on density relationships explained 94% of the variance in population trend.

A key-factor analysis of population fluctuations in Andraca bipunctata Walker (Lepidoptera: Bombycidae)

1979 ◽  
Vol 69 (1) ◽  
pp. 195-201 ◽  
Author(s):  
B. Banerjee
Keyword(s):  
Factor Analysis ◽  
Statistical Tests ◽  
Population Fluctuations ◽  
Female Mortality ◽  
Mortality Factors ◽  
Density Dependent ◽  
Key Factor ◽  
Key Factor Analysis ◽  
Insect Populations ◽  
Sampling Procedures

AbstractThe causes of fluctuation and stabilisation in a population of Andraca bipunctata Wlk. on tea in India were assessed over three years using the technique of key-factor analysis. Failure to produce the maximum complement of eggs, together with female mortality and adult migration, is shown to be the key-factor. Other mortality factors include non-viability of eggs and parasitism of the caterpillars by the tachinid Cylindromyia sp. Mortality of the female pupae tends to stabilise the population by compensating for losses due to the key-factor, but neither this nor any other mortality factors appear to be significantly density-dependent. The need for devising specialised sampling procedures and statistical tests for tropical insect populations is discussed.

Argentine stem weevil (Listronotus bonariensis, Coleoptera: Curculionidae) population dynamics in Canterbury, New Zealand dryland pasture

2010 ◽  
Vol 101 (3) ◽  
pp. 295-303 ◽  
Author(s):  
S.L. Goldson ◽  
M.C. Barron ◽  
J.M. Kean ◽  
C. van Koten
Keyword(s):  
Population Dynamics ◽  
New Zealand ◽  
Population Analysis ◽  
Larval Survival ◽  
Compensatory Response ◽  
The North ◽  
Key Factor ◽  
Listronotus Bonariensis ◽  
Pupal Mortality ◽  
Microctonus Hyperodae

AbstractThe Argentine stem weevil (Listronotus bonariensis) was an economically important pest in New Zealand pastures until the release of the parasitoidMicroctonus hyperodae. This contribution uses historical data to investigate the regulation of the pest populations prior to, and somewhat during, the establishment of this parasitoid in dryland Canterbury, New Zealand. Thus, a significant goal of this study is to provide anL. bonariensispopulation dynamics baseline for any future work that aims to analyse the full effects ofM. hyperodaeon the weevil, now that equilibrium with the weevil host has been reached.The population dynamics ofL. bonariensis, based on a life-table approach, were investigated using data collected regularly for eight years from populations in Canterbury, New Zealand. The key factor affecting end-of-seasonL. bonariensisdensity was found to be variation in second generation fourth instar prepupal and pupal mortality. This may have been caused by arrested development and ongoing mortality resulting from the onset of cooler autumnal conditions.A compensatory response was found in recruitment to the second summer weevil generation, whereby the realised fecundity of the emergent first summer generation of weevils was found to be negatively related to the density of adult weevils per ryegrass tiller. This is the first time that this has been found via long-term population analysis ofL. bonariensis, although indications of this have been found elsewhere in caging, pot and small plot experiments.In this study, the effect of the parasitoid biocontrol agentMicroctonus hyperodaeonL. bonariensispopulation dynamics was unclear, as the analysis covered a period when the parasitoidMicroctonus hyperodaewas introduced and still establishing. It does, however, raise important questions for future analysis in terms of the interaction between parasitism and unrealised fecundity.The results in this contribution also highlighted regional differences. Overwintering mortality of adult weevils in Canterbury was constant between years, whilst earlier studies in the North Island Waikato region indicated this mortality was density dependent. In addition, the availability of tillers in endophyte-free ryegrass pastures in Canterbury had no influence on egg and early-instar larval survival, which contrasts with the finding from endophytic Waikato pastures.

Contemporaneous Mortality Factors in Population Dynamics

1965 ◽  
Vol 97 (11) ◽  
pp. 1173-1184 ◽  
Author(s):  
R. F. Morris
Keyword(s):  
Population Dynamics ◽  
Statistical Inference ◽  
Direct Observation ◽  
General Equation ◽  
Population Data ◽  
Interaction Coefficient ◽  
Field Population ◽  
Population Trend ◽  
Mortality Factor ◽  
Mortality Factors

AbstractThe effect of any mortality factor on population trend is influenced greatly by other factors that operate contemporaneously within the same age interval, and by the extent to which it interacts with these other factors. A general equation which makes provision for different degrees of interaction is proposed as a simplified first step in the study of interaction, and some theoretical examples are presented to illustrate the importance of the interaction coefficient. Methods for obtaining estimates of the coefficient, both through statistical inference from field population data and through direct observation and experimentation, are discussed.

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