The Life System of Cardiaspina Albitextura (Psyllidae), 1950-74.

1975 ◽  
Vol 23 (4) ◽  
pp. 523 ◽  
Author(s):  
LR Clark ◽  
MJ Dallwitz
Keyword(s):  
Population Density ◽  
Natural Enemies ◽  
Average Rate ◽  
The Other ◽  
Population Densities ◽  
Insect Abundance ◽  
Complete Development ◽  
Rate Of Increase ◽  
Adverse Weather ◽  
Survival And Reproduction

In 1958-63 and 1964-71 the life systems of four kinds of test-forming psyllid that coexist on Eucalyptus blakelyi were investigated intensively in a comparative study of insect abundance. This paper deals mainly with C. albitextura, which was kept under observation from 1950 to 1974. (The others were two species of Glycaspis, Spondyliaspis sp, and Creiis costatus.) The results indicate that the differences in maximal abundance reached by the four kinds of psyllid are mainly the outcome of differences in their ability tg utilize the leaves of the host plant as a source of food, C. albitextura being much more effective than the other species. For the latter, it appears that the principal environmental determinant of abundance was the number of feeding places where nymphs could survive long enough to complete development. That number varied according to foliage and weather. C. albitextura also differed from the other species by having its population densities held for long periods far below the levels at which the food supply would be limiting, by restrictions imposed upon reproduction by adverse weather and foliage conditions (the latter being due partly to poor synchronization between the emergence of adults in spring and the occurrence of foliage attractive for oviposition), and by high mortalities due to natural enemies. The life system of C. albitextura lacks an element that can stabilize abundance at low population densities, but adverse environmental influences usually limit the rate of increase greatly when abundance is low. The magnitude of the average rate of increase to high levels of population density, and the length of time for which high average densities are maintained, depend upon the frequency with which favourable conditions of weather, foliage and predation combine to promote both survival and reproduction.

Estimating Population Densities of Root Lesion Nematodes, Pratylenchus spp., from Soil Samples Using Dual Active and Passive Assays

2012 ◽  
Vol 13 (1) ◽  
pp. 4 ◽  
Author(s):  
Ann E. MacGuidwin ◽  
Breann E. Bender
Keyword(s):  
Population Density ◽  
Soil Samples ◽  
Scaling Factor ◽  
The Other ◽  
Testing Methods ◽  
Population Densities ◽  
Lesion Nematodes ◽  
The Mean ◽  
Time Of Year ◽  
Root Lesion Nematodes

Root lesion nematodes are versatile parasites that move freely between root and soil habitats. Most laboratories conduct separate assays for soil or root tissue, using time-of-year as the selecting factor. We used a dual assay that simultaneously extracts nematodes from soil and root fragments in soil samples to identify the value of soil versus root tests using 920 research samples collected 1 April to 15 May, and 853 clinic samples collected year round. Nematodes were recovered from both soil and root fragments regardless of the time of year or origin of the sample. When the data were summarized by cohort, the mean percentage of nematodes recovered from root fragments was 65% for the research samples, 59% for clinic samples submitted 1 March to 15 June, 56% for clinic samples submitted 16 June to 31 July, and 49% for clinic samples submitted after 1 August. Both the incidence and population density of root lesion nematodes was underestimated if only the soil or only the root fraction was considered, indicating the need for testing methods that consider both habitats. The variability among samples for the distribution of nematodes between root and soil habitats was high, negating the option of running one assay and using a constant scaling factor to account for the other. Accepted for publication 30 October 2012. Published 20 November 2012.

The effect of topdressed superphosphate on changes in nitrogen:carbon:sulphur: phosphorus and pH on a red earth soil during a long term grazing experiment

Soil Research ◽  
1977 ◽  
Vol 15 (2) ◽  
pp. 147 ◽  
Author(s):  
GD Kohn ◽  
GJ Osborne ◽  
GD Batten ◽  
AN Smith ◽  
WJ Lill
Keyword(s):  
Average Rate ◽  
C:N Ratio ◽  
Rate Of Change ◽  
The Other ◽  
Wagga Wagga ◽  
Grazing Experiment ◽  
Rate Of Increase ◽  
Red Earth ◽  
Stocking Rates

Increases in total nitrogen in a grazing experiment at Wagga Wagga (N.S.W.) over the years 1962-1966 were related to the levels of superphosphate applied (0-375 kg ha-1), the average rate of increase being 59 kg ha-1 year-1. The rate of change varied between years and was negative in a dry year. Total sulphur levels were not influenced by phosphate treatments (mean 150 ppm), but sulphate sulphur was only maintained by the highest superphosphate level. Total, aluminium, iron, calcium and 'available' phosphate increased with superphosphate levels. The level of aluminium-bound phosphate increased more rapidly than the other fractions. In the treatments without applied phosphate the aluminium bound phosphate declined more rapidly than the other fractions. Organic carbon was not influenced by treatments but showed an increase with time. The C:N ratio declined from 13 to 11.8 during the experiment. Soil pH declined by 0.18 pH units, but this was not affected by superphosphate levels. Stocking rates had no effect on these parameters of soil fertility.

Expression of autogeny in relation to larval population density of Sarcophaga bullata Parker (Diptera: Sarcophagidae)

1973 ◽  
Vol 51 (11) ◽  
pp. 1189-1193 ◽  
Author(s):  
J. A. Baxter ◽  
A. M. Mjeni ◽  
P. E. Morrison
Keyword(s):  
Population Density ◽  
The Other ◽  
Larval Rearing ◽  
Population Densities ◽  
Larval Population ◽  
Sarcophaga Bullata ◽  
Other Hand ◽  
Rearing Conditions

The expression of autogeny in S. bullata was influenced by the larval rearing conditions. Low larval population densities resulted in large flies that were autogenous. On the other hand, high larval population densities produced small flies that were anautogenous, In anautogenous females the size and stage to which the follicles developed varied with the size of the fly. When reared on a sucrose–water diet, the females from an intermediate larval population density possessed larvae, mature eggs, degenerate follicles, or undeveloped follicles.

Skin follicle types, ratios, and population densities in Rajasthan sheep breeds

1960 ◽  
Vol 11 (3) ◽  
pp. 408 ◽  
Author(s):  
S Narayan
Keyword(s):  
Population Density ◽  
The Other ◽  
Population Densities ◽  
Primary Follicle ◽  
Sheep Breeds ◽  
Body Regions ◽  
Three Body

Observations are reported of skin follicle types, ratios, population densities, and percentages of medullated fibres in four Rajasthan sheep breeds – Chokla, Marware, Jaisalmere, and Malpura. Data from three body regions – shoulder, side, and breech – were available for a total of 21 sheep, and for 12 more there were observations for at least one of the three regions. The Chokla breed had the highest total and highest primary follicle population density (9.4 and 3.1 per mm2 respectively), as well as the highest ratio of secondary to primary follicles (2.1) and the lowest percentage medullation (24 per cent. of all fibres, 2 per cent. of secondary fibres). The Malpura breed had the lowest total and lowest primary follicle population density (5.6 and 2.5 per mm2), and was equal with the Marware breed for the lowest ratio (1.3). The Malpura breed had the highest percentage medullation (77 per cent. of all fibres, 60 per cent. of secondary fibres). Of the three body regions studied, the side had the highest ratio of secondary to primary follicles in all four breeds, while the breech had the highest percentage of medullated secondary fibres. The percentage of medullated primary fibres in the breech was equal to or greater than that in either of the other regions.

scholarly journals Determining carrying capacity from foraminiferal time-series

2012 ◽  
Vol 31 (2) ◽  
pp. 111-119 ◽  
Author(s):  
Brent Wilson ◽  
Benjamin P. Horton
Keyword(s):  
Time Series ◽  
Population Density ◽  
Carrying Capacity ◽  
Rate Of Change ◽  
Negative Slope ◽  
Population Densities ◽  
Intraspecific Interactions ◽  
Rate Of Increase ◽  
Capita Rate ◽  
Per Capita

Abstract. The carrying capacity K is the equilibrium population density of a species that an area can support while adequately meeting the needs of every individual. Although widely used in ecology, it has yet to be applied rigorously to living foraminifera. K is readily determined from time-series of population densities. Given that Nt+1 = Nt + RNt, in which Nt is the population densities at time t, Nt+1 is the density at a subsequent time t+1 and R is the per capita rate of change in population density, then linear regression gives Rt = Rm − sNt, in which Rt is the per capita rate of increase at time t, the constant Rm is the maximum possible individual rate of increase, and the negative slope s represents the strength of intraspecific interactions. Setting Rt = 0, so that Nt = K and Rm – sK = 0, gives K = Rm/s, which is applicable in aseasonal environments. There are two carrying capacities in seasonal environments, depending on whether the season is favourable (Kmax) or unfavourable (Kmin). Values of Kmax and Kmin are estimated for Nonion depressulus in the Exe estuary, UK (25 monthly samples), Quinqueloculina spp. in the Indian River Lagoon, USA (60 monthly samples) and Haynesina germanica in Cowpen Marsh, UK (25 fortnightly samples). The most precise estimate was for H. germanica, but it was unclear if this was due to the high rate of sampling or the large number of replicates used to erect this time-series.

Ambient Humidity Affects Development, Survival, and Reproduction of the Invasive Fall Armyworm, Spodoptera frugiperda (Lepidoptera: Noctuidae), in China

2021 ◽  
Author(s):  
Limei He ◽  
Shengyuan Zhao ◽  
Abid Ali ◽  
Shishuai Ge ◽  
Kongming Wu
Keyword(s):  
Spodoptera Frugiperda ◽  
Fall Armyworm ◽  
Intrinsic Rate ◽  
Intrinsic Rate Of Increase ◽  
Reproduction Rate ◽  
Ambient Humidity ◽  
Rate Of Increase ◽  
Population Forecasting ◽  
Survival And Reproduction ◽  
Net Reproduction

Abstract Ambient humidity can directly affect the water balance in insects. The migratory fall armyworm, Spodoptera frugiperda Smith, has spread to more than 60 countries and regions in Africa, Asia, and Oceania that have a great difference in average ambient humidity. Understanding the effects of ambient humidity changes on its development, survival, and reproduction can help to predict its population dynamics in different habitats. Therefore, we evaluated the effects of atmospheric relative humidity (RH) on the development, survival, and reproduction and soil moisture on the pupation and emergence of fall armyworm. As a result, survival and pupal mass increased significantly with increasing RH. Among the five RHs tested, 80% RH was the most suitable for fall armyworm with the highest intrinsic rate of increase (r), finite rate of increase (λ), and net reproduction rate (R0). The population growth at the different RHs in decreasing order was 80 > 100 > 60 > 40 > 20%. A relative moisture (RM) of soil from 6.80 to 47.59% was suitable for fall armyworm pupation, survival, and eclosion, but fall armyworm could not pupate normally in soil with 88.39 and 95.19% RM. The survival and emergence rate of fall armyworm pupae were reduced by irrigation that increased the RM after the mature larvae entered the soil. These findings may be helpful for refining laboratory rearing protocols, population forecasting, and management of fall armyworm.

scholarly journals Intercropping Rosemary (Rosmarinus officinalis) with Sweet Pepper (Capsicum annum) Reduces Major Pest Population Densities without Impacting Natural Enemy Populations

Insects ◽  
2021 ◽  
Vol 12 (1) ◽  
pp. 74
Author(s):  
Xiao-wei Li ◽  
Xin-xin Lu ◽  
Zhi-jun Zhang ◽  
Jun Huang ◽  
Jin-ming Zhang ◽  
...  
Keyword(s):  
Integrated Pest Management ◽  
Pest Management ◽  
Pest Control ◽  
Natural Enemies ◽  
Natural Enemy ◽  
Sweet Pepper ◽  
Population Densities ◽  
Pest Population ◽  
Major Pest ◽  
Population Suppression

Intercropping of aromatic plants provides an environmentally benign route to reducing pest damage in agroecosystems. However, the effect of intercropping on natural enemies, another element which may be vital to the success of an integrated pest management approach, varies in different intercropping systems. Rosemary, Rosmarinus officinalis L. (Lamiaceae), has been reported to be repellent to many insect species. In this study, the impact of sweet pepper/rosemary intercropping on pest population suppression was evaluated under greenhouse conditions and the effect of rosemary intercropping on natural enemy population dynamics was investigated. The results showed that intercropping rosemary with sweet pepper significantly reduced the population densities of three major pest species on sweet pepper, Frankliniella intonsa, Myzus persicae, and Bemisia tabaci, but did not affect the population densities of their natural enemies, the predatory bug, Orius sauteri, or parasitoid, Encarsia formosa. Significant pest population suppression with no adverse effect on released natural enemy populations in the sweet pepper/rosemary intercropping system suggests this could be an approach for integrated pest management of greenhouse-cultivated sweet pepper. Our results highlight the potential of the integration of alternative pest control strategies to optimize sustainable pest control.

Effects of crop sequence and rainfall on population dynamics of Fusarium solani f.sp. phaseoli in soil

1992 ◽  
Vol 70 (10) ◽  
pp. 2005-2008 ◽  
Author(s):  
Robert Hall ◽  
Lana Gay Phillips
Keyword(s):  
Population Dynamics ◽  
Phaseolus Vulgaris ◽  
Population Density ◽  
Fusarium Solani ◽  
Population Densities ◽  
Total Rainfall ◽  
Colony Forming Units ◽  
Bean Crop ◽  
Previous Summer ◽  
Crop Sequence

Evidence is presented that population dynamics of Fusarium solani f.sp. phaseoli in soil depend on the effects of crop sequence and rainfall on parasitic activities of the pathogen. In a rotation trial started in 1978 and conducted over 14 years, population densities (colony-forming units/g) of the fungus in soil remained below 50 in treatments (fallow, repeated corn, repeated soybean) where the preferred host plant (common bean, Phaseolus vulgaris) was not grown. Where bean was grown every 3rd year or every year, population densities reached 475 and 660, respectively, by 1984. Thereafter, population densities of the fungus fluctuated widely from year to year in both rotation and repeated bean treatments. In the rotation treatment, peaks in population density of the pathogen coincided with the years of bean production. In repeated bean plots between 1985 and 1991, population density of the fungus in June was significantly correlated (r = 0.77, p = 0.04) with total rainfall received during the previous summer (June–August). It is postulated that higher rainfall during the growing season of the bean crop stimulated root growth and root infection, leading to the accumulation of higher levels of potential inoculum in infected tissue and the release of higher levels of inoculum into the soil by the following June. Key words: Fusarium solani f.sp. phaseoli, bean, Phaseolus vulgaris, rainfall, crop rotation.

Population Densities Allowed Around Dutch SEVESO Establishments

2000 ◽  
Author(s):  
G. M. H. Laheij ◽  
B. J. M. Ale ◽  
J. G. Post
Keyword(s):  
Population Density ◽  
The Netherlands ◽  
Individual Risk ◽  
Population Densities ◽  
Planning Policy ◽  
Relative Contribution ◽  
Societal Risk ◽  
Dangerous Substances ◽  
The Individual ◽  
Uniform Population

Abstract In the Netherlands, the individual risk and societal risk are used in efforts to reduce the number of people exposed to the effect of an accident at an establishment with dangerous substances. To facilitate the societal risk planning policy an investigation was carried out for the Dutch SEVESO establishments to investigate the possibility of determining a generic uniform population density for the zone between the individual risk contours of 10−5 and 10−6 per year. The indicative limit for the societal risk at this density was not to be exceeded. Also there was to be enough space left for a significantly higher population density outside the individual risk contour of 10−6 per year. The RORISC methodology and the actual data for the 124 Dutch SEVESO establishments were used to determine the generic uniform population density. Based on the data available it can be concluded that the maximum allowed uniform population density in the zone between the individual risk contours of 10−5 and 10−6 per year is lower than one person per hectare. At this density there is no space left for a higher population density outside the individual risk contour of 10−6 per year. For uniform population densities the relative contribution to the societal risk has been found significant up to the individual risk contour of 10−7 per year.

Sign in / Sign up

Export Citation Format

Share Document