Modelling selection for resistance to methods of insect pest control in combination

The development of resistance to insecticides is now widespread among insects. Other methods of pest control are also potentially at risk of encountering resistance. A modelling approach is presented here to evaluate the effects of combining methods of insect pest control on the selection for resistance to the control methods. This analysis is based on partitioning the total mortality acting on a population into its constituent components from all known sources, and these are related to selection for resistance. When two control methods are used in combination, selection for resistance against the two is a linear function if the two don't interact, otherwise it may be sublinear or supralinear. A specific example is presented using a model of the Olive fruit fly (Dacus oleae Gmel.) and employing food-baited and pheromone-baited traps for control. The control methods that appear least likely to encounter resistance are natural enemies and the use of pheromone traps for male annihilation. These should be integrated into a control program where possible to minimize the development of resistance to other control methods being used.     

Modelling the effects of population aggregation on the efficiency of insect pest control

Summary A methodology is developed to assess the effects of spatial distribution on the efficiency of insect pest control. This methodology is especially applicable to pest control methods whose efficiency of action depends either positively or negatively on pest density It is applied here to the sterile insect technique and pheromone trapping for male annihilation, which both depend negatively on density. This methodology relies on quantifying clumps of various size and then relating this to efficiency of control and predicting the total pest production given the information on clump sizes and efficiency of control for each clump size. It is found that control is about four times as difficult for a population that is highly clumped (k of the negative binomial distribution=0.25) as for a regularly dispersed population.     

Combining pheromone-baited and food-baited traps for insect pest control: Effects of additional control by parasitoids

Summary Two age-structured population dynamic models are analyzed in which pheromone-baited trapping and food-baited trapping are used simultaneously to eradicate an insect pest. The pest species is assumed to be under partial control by a host-specific parasitoid species. The two models assume that density-dependent population regulation is accomplished either by host larval competition or by means of oviposition interference among the parasitoids. The two trap types interact in a positive synergistic manner and this combination appears to be very promising as a useful combination of pest control methods. Several features of the system are examined; the feature which appears to cause the greatest problem is the possibility of the parasitoids being attracted to the pheromone or the food traps. In either case, the degree of attraction does not have to be very great to undermine the control effort. It is seen that food trapping becomes indispensible if host pheromone is used by the parasitoids as a host-locating kairomone. If odor in the food traps is used by the parasitoids as kairomone, then the situation appears more optimistic, as the reduction in efficiency of the food traps appears much less than with the pheromone traps when pheromone acts as kairomone.     

The completeness of enumeration in the 1973 census of the population of Colombia

The effort is made to determine the true size and distribution by age and sex of the population of the Republic of Colombia in October 1973. After initially arriving at estimates of the levels of fertility and mortality during the intercensal period and then correcting the 1964 census population for age misreporting and selective undernumeration of males, a hypothetical populaiton corresponding to October 1973 is constructed. Comparing the constructed population with the population observed in the census yelds an estimate of completeness of enumeration in 1973 that is relative to the enumeration of females in 1964. This estimate is obtained under the assumption that net international migration during the period was of negligible importance. As there is reason to believe that this is not a valid assumption and upon examining the limited amount of evidence available, speculaitons are made concerning the amount of net out-migration to have occurred during the 1964-1973 period and the size of the coresponding modificaiton in the estimate of completeness of enumeration. After adjusting for underenumeration of males in 1964 and neglecting the impact of international migration, a theoretical 1973 census population of 23,201,000 was estimated. Apart from the total number of people enumerated, the information that was analyzed from the advance sample appears to be of good quality, at least in relation to prior censuses. The estimates of fertility and mortality reveal an important decline in Colombian fertility. By coming up with separate estimates of infant and childhood and adult mortality, it has been possible to shed new light on the shape and the level of mortality in Colombia. The new Brass method for estimating adult mortality provides reliable results even when mortality has been declining, and there are recognizable distortions in the distribution of the population by age.     

Combining pheromone-baited and food-baited traps for insect pest control: Effects of developmental period

Summary An age-structured population dynamics model is presented that incorporates pheromone-trapping and food-trapping as control methods for an insect pest. The model yields the following results. Low rates of pest survivorship allow lower trapping rates for control. Species with long developmental periods are easier to control than those with shorter developmental periods (other factors being equal) due to lower net survival. The rates of pheromone trapping alone for effective control are usually very high. The combination of pheromone and food trapping allows control with much lower trapping rates than either method alone. Even small amounts of immigration of adult pests into the control area renders pheromone control ineffective, whereas food traps suppress both the immigrants and the resident population. Food- (or odor-) baited traps which attract both males and females are only somewhat more efficient than those which attract females alone. The existence of density-dependent population regulation assists the control program substantially, but this assistance declines as food trapping becomes a more important part of the control program. Larval competition strongly affects the required trapping rates for eradication; species in which all larvae exert strong competition are much easier to control than those in whic the younger larvae contribute little to the total competitive depression.     

A granulosis virus, possible biological agent for control ofAdoxophyes orana (Lepidoptera: Tortricidae) in apple orchards

Summary Based on the results of ecological surveys ofAdoxophyes orana and its natural enemies in apple orchards sprayed with the granulosis virus and control plots, we constructed working models to simulate the population dynamics in three different experimental plots; those treated with chemical insecticides, those with granulosis virus, and controls. The number of individuals killed by predators, parasitoids and by miscellaneous mortality factors could be calculated on the assumption of imperfect density relations; that is, relation of the number killed by each factor with the initial number of larvae was represented by a curve with an upper asymptote. We could estimate the proportion of virus infection using curves with upper asymptotes. Rate of increase from pupa to middle instar larvae of the next generation was subject to strong density-effect. Simulation we proposed in this paper suggests a possibility that a single spray of the virus at 1st generation can reduce not only the number ofA. orana larvae in the 2nd and 3rd generations but also the degree of fruits injured by this insect. Spray of chemical insecticide is considered to be ineffective in reducing the pest density and the degree of injury to low levels in subsequent generations, as compared with untreated plot, where the density of the 1st generation larvae is low.     

Age,period, and cohort effects in demography: a review

This paper considers only the vital events of demographic measurement, the factors influencing the rate at which those events occur and then investigates the consequences of patterns of these events. It reviews the state of the art of age, period and cohort analysis for demographic dependent variables. Major examples of such analyses are given in both mortality and fertility studies. In the area of mortality the conventional approach to such analysis apears to be well suited to a wide range of applications yielding useful results. The reasons for this suitability are: early childhood experience is important in many major disease and death processes, so that cohorts are legitimately viewed as acquiring early on a certain fixed susceptibility; data sometimes stretch back far enough that stationary standards of age patterns can be developed empirically, and applied to later experience; and, logarithmic or logistic transformations linearize comparisons of age schedules or mortality so that standard statistical procedures are suitable. Applications of age, period, and cohort analysis are not always routine; external constraints are required, in the form of theoretically based and mathematically expressed age patterns of mortality, in order to distinguish effectively between period and cohort effects. A set of models of age patterns of mortality that are based on cohort as well as period experience could be constructed with useful applications. With fertility analysis the conventional approach is much less suitable. Once goal directed behavior is introduced, empirical examinations must be based on theories or assumptions about how such goals are formulated and pursued. Conventional analysis might suffice only if one is prepared to accept the assumption that all pertinent goals and strategies are formulated before the initiation of childbearing and remain unaffected by subsequent events. This assumption is untenable for modern developed populations and the forms of analysis appropriate to age period cohort investigations of fertility will have to develop along with theories of reproductive behavior.     

Estimation of average mortality under censoring and truncation

In demography mortality is usually reported through averages over time intervals. If average mortality is estimated from censored or truncated data, then direct methods of estimation may create biases that depend on the censoring or truncation distribution. Such discretization errors may be avoided by estimating survival curves first in continuous time, and then discretizing the estimators. We illustrate the different methods on data of the form obtained from family reconstitution.     

Pest population stability under sterile releases

Summary The stability of a pest population is one of the critical features to be examined when considering a control strategy for a given pest species. Four models involviing sterile male releases are examined for various stability characteristics; the models examined were: (i) a simple one stage model with no species interactions, (ii) a two life-stage model, (iii) a model involving two competing species, (iv) a model in which the pest is under predation. Of the four, the simple model was the most stable and the predation model was the least stable under continued sterile releases.     

A model for analyzing insect stage-frequency data when mortality varies with time

Summary A model is developed for the analysis of insect stage-frequency data which may be applied to populations with age-dependent mortality. The analysis of stage-frequency data is divided into two steps. In the first step, the number of different mortality rates and their values are estimated. The second step provides estimates of developmental rates and variances for each developmental stage and in addition provides estimates of the number of recruits to each stage. The model may be used both in analysis and prediction of insect stage frequencies. Hence, in addition to estimating developmental and mortality rates from stage-frequency data, it may also be used as a simulation model for an insect population. The model is applied to two populations ofHemileuca oliviae Cockerell, a lepidopterous pest of New Mexico grasslands. The model identifies, in the two populations, different mortality rates that are related to plant productivity.     

United Nations/World Health Organization Meeting on Socio-Economic Determinants and Consequences of Mortality,Mexico City, 19-25 June 1979

The objectives of the United Nations/World Health Organization (WHO) Meeting on Socioeconomic Determinants and Consequences of Mortality, held in Mexico City in June 1979, were the following: to review the knowledge of differential mortality and to identify gaps in the understanding of its socioeconomic determinants and consequences; to discuss the methodological and technical problems associated with data collection and analysis; to consider the policy implications of the findings presented and to promote studies on the implications of socioeconomic differentials in mortality on social policy and international development strategies; to formulate recommendations and guidelines for the utilization of the 1980 round of population censuses for in-depth studies of mortality differentials; and to stimulate national and international research on differential mortality. Participants discussed the state of knowledge of socioeconomic differentials and determinants of mortality and described the socioeconomic measures available, the methods of data collection and analysis used, and the findings themselves. A number of characteristics had been employed in the study of differential mortality, and these could be grouped under the following headings: occupation; education; housing; income, wealth; family size; and place of residence. The techniques or methods used to analyze mortality were direct and indirect methods, and these are examined. Inequalities in mortality were found to be closely associated with inequalities in social and economic conditions. Any effort to reduce or remove those inequalities would have to be based on a clear understanding of their causes and interrelationships in order to succeed. Participants indicated a desire to see a resurgence of mortality research, and some research suggestions are outlined.     

Assessing Changes in Household Socioeconomic Status in Rural South Africa, 2001–2013: A Distributional Analysis Using Household Asset Indicators

Understanding the distribution of socioeconomic status (SES) and its temporal dynamics within a population is critical to ensure that policies and interventions adequately and equitably contribute to the well-being and life chances of all individuals. This study assesses the dynamics of SES in a typical rural South African setting over the period 2001–2013 using data on household assets from the Agincourt Health and Demographic Surveillance System. Three SES indices, an absolute index, principal component analysis index and multiple correspondence analysis index, are constructed from the household asset indicators. Relative distribution methods are then applied to the indices to assess changes over time in the distribution of SES with special focus on location and shape shifts. Results show that the proportion of households that own assets associated with greater modern wealth has substantially increased over time. In addition, relative distributions in all three indices show that the median SES index value has shifted up and the distribution has become less polarized and is converging towards the middle. However, the convergence is larger from the upper tail than from the lower tail, which suggests that the improvement in SES has been slower for poorer households. The results also show persistent ethnic differences in SES with households of former Mozambican refugees being at a disadvantage. From a methodological perspective, the study findings demonstrate the comparability of the easy-to-compute absolute index to other SES indices constructed using more advanced statistical techniques in assessing household SES.     

Estimating Mortality Differences in Developed Countries From Survey Information on Maternal and Paternal Orphanhood

In general, the use of indirect methods is limited to developing countries. Developed countries are usually assumed to have no need to apply such methods because detailed demographic data exist. However, the potentialities of demographic analysis with direct methods are limited to the characteristics of available macro data on births, deaths, and migration. For instance, in many Western countries, official population statistics do not permit the estimation of mortality by socioeconomic status (SES) or migration background, or for estimating the relationship between parity and mortality. In order to overcome these shortcomings, I modify and extend the so-called orphanhood method for indirect estimation of adult mortality from survey information on maternal and paternal survival to allow its application to populations of developed countries. The method is demonstrated and tested with data from two independent Italian cross-sectional surveys by estimating overall and SES-specific life expectancy. The empirical applications reveal that the proposed method can be used successfully for estimating levels and trends of mortality differences in developed countries and thus offers new prospects for the analysis of mortality.     

One step back in understanding racial differences in birth weight

In recognition of the biological and social connections in demographic processes, demographers have integrated biological factors into their models of population variation. This new effort has tended to focus on the analysis of fertility and mortality. Edwin J.C.G. van den Oord and David C. Rowe's article, "Racial Differences in Birth Health Risk: A Quantitative Genetic Approach," published in the August 2000 issue of Demography, is part of this effort. These authors use race as a proxy for genetic variation, which subverts even the most positive attempts to understand the impact of genetic variation on demographic processes. The authors' statistical results restate their anachronistic theory of race using latent variables that are not open to empirical testing. Although new data increase the opportunities for the examination of the relationship between biology and demographic processes researchers must be vigilant not to commit the errors of the past by misusing race as a variable.     

A Flexible Bayesian Model for Estimating Subnational Mortality

Reliable subnational mortality estimates are essential in the study of health inequalities within a country. One of the difficulties in producing such estimates is the presence of small populations among which the stochastic variation in death counts is relatively high, and thus the underlying mortality levels are unclear. We present a Bayesian hierarchical model to estimate mortality at the subnational level. The model builds on characteristic age patterns in mortality curves, which are constructed using principal components from a set of reference mortality curves. Information on mortality rates are pooled across geographic space and are smoothed over time. Testing of the model shows reasonable estimates and uncertainty levels when it is applied both to simulated data that mimic U.S. counties and to real data for French départements. The model estimates have direct applications to the study of subregional health patterns and disparities.     

Place and Child Health: The Interaction of Population Density and Sanitation in Developing Countries

A long literature in demography has debated the importance of place for health, especially children’s health. In this study, we assess whether the importance of dense settlement for infant mortality and child height is moderated by exposure to local sanitation behavior. Is open defecation (i.e., without a toilet or latrine) worse for infant mortality and child height where population density is greater? Is poor sanitation is an important mechanism by which population density influences child health outcomes? We present two complementary analyses using newly assembled data sets, which represent two points in a trade-off between external and internal validity. First, we concentrate on external validity by studying infant mortality and child height in a large, international child-level data set of 172 Demographic and Health Surveys, matched to census population density data for 1,800 subnational regions. Second, we concentrate on internal validity by studying child height in Bangladeshi districts, using a new data set constructed with GIS techniques that allows us to control for fixed effects at a high level of geographic resolution. We find a statistically robust and quantitatively comparable interaction between sanitation and population density with both approaches: open defecation externalities are more important for child health outcomes where people live more closely together.     

A life table for a West Indian slave population

This note comments briefly on the system of slave registration set up in the British colonies, and deals in particular with the data tabulated for the British Guiana slave population in the Parliamentary Papers, 1833. From the age distributions given there a life table has been constructed by a census differencing method. This life table shows the extremely high mortality then being experienced by slave populations in the West Indies.     

Life table construction on the basis of two enumerations of a closed population

The author demonstrates that an accurate detailed life table that represents average mortality experience between two censuses can be constructed if the censuses provide accurate records of the single-year age distribution of a closed population. This life table can begin at age zero if accurate data on the annual number of births during the inter-censal period are available; otherwise the first age in the life table must equal the duration of time between the censuses. "The estimation technique involves the calculation of the number of persons attaining each age during the period between the censuses and the determination of the average rate of increase in the number at each individual age. The success of the technique comes from the use of interpolation to calculate how many in each cohort attain each exact age the cohort passes through between the censuses." The estimation technique is tested using two alternative methods of interpolation. Some illustrations based on data for Sweden and China are included.     

For controlling population growth more scientifically]

The February 4, 1982 edition of the People's Daily published a directive of the State Council of the Central Committee of the Chinese Communist Party regarding going a step further in the work of birth control. The spirit of the directive is to adapt to new situations and to push forward the work of birth control. Since the late 1970s, the success of birth control has been seen in the decline of the rate of natural population growth. Birth control work is affected by the new circumstances that rose with the effort to raise economic standards. For instance, the system of fixed responsibility in production that is being implemented in the villages benefits population control. That is, a developing agarian economy can alleviate the problem of supporting the aged, dispel the anxieties of future care of the elderly, and build up a dependable material basis. The spirit of the directive is based on objective truths, as is the control of population growth and the implementation of birth control work. If birth control can succeed in the countryside where 800 million peasants reside, then there is hope for attaining the goals of population control; but, there are differences between urban and rural settings, and the methods for population control cannot be the same for both situations. Nor can it be the same for China's minorities, whose population control programs must be tailored to their particular needs. Meeting the population needs of varying situations with different solutions is more scientific and realistic. The task of controlling population growth is formidable, but the following favorable conditions will facilitate the work: 1) party and governmental support is great, and population planning is an integral part of economic and social planning; 2) birth control organizations exist at all levels; 3) there exists high social and political consciousness among disciplined masses; and 4) there is a body of accumulated experience from which to draw.     

Mortality and fertility in Arctic Communities Greenland - A case study

Summary The purpose of this paper is to estimate the present level of mortality and fertility as well as its history amongst the indigenous population of Greenland during the period 1834-1953 on the basis of a series of censuses taken during that time. Mortality and fertility parameters have been estimated by techniques particularly suited for the analysis of incomplete demographic data - e.g. stable population analysis. During the period studied Greenland was a Danish colony. It did not become constitutionally part of Denmark until 1953. The paper shows that even though the importance of Danish - and other European - influence should not be underestimated, the socio-economic structure of Greenland was relatively stable until 1953. The results show an extremely high mortality and a correspondingly high fertility. There is also evidence that mortality fluctuated considerably during the period. This might also be true of fertility, but it is impossible to establish this by means of the techniques used. These results are supported by an analysis of registrations of births and deaths for part of the period. The paper concludes with an evaluation of the validity of the techniques of estimation, having regard to the nature of the Greenland censuses. It is pointed out that the empirical material from which model stable populations must have been constructed varies somewhat from that applicable to an Arctic population.