There are numerous examples of relatively minor insect species that have become important pests as a result of environmental change. The alfalfa butterfly Colias eurytheme presents a similar story. By its very nature, modern agriculture provides opportunities for insect populations that they would never encounter under "natural" conditions.
In Depth Tutorials and Information Population Ecology Insects Population ecology deals with questions related to the density or number of individuals of a species in a habitat or location.
Insect population ecologists try to understand why population densities of some insects fluctuate dramatically, but others show little variation in density. They want to know why some species are rare, whereas others are common.
They seek to understand the mixture of factors affecting mortality and fecundity that together determine the characteristic density of a species and whether the density will decline or increase. Applied population ecologists try to understand the conditions that allow densities of pest insects to reach damaging levels, and they seek to modify those conditions to keep the densities below those levels.
To isolate the effects of particular variables from the multitude of factors influencing population growth and survival, population ecol-ogists apply a range of tools to understand population systems, including gathering data on density, fecundity, and mortality from natural populations, construction of mathematical models of population interactions, and experimental manipulation of populations in the field.
When the habitat has definable boundaries, we can estimate the number of individuals in the population. More frequently, we estimate density or number of individuals per unit of habitat. Sampling methods vary tremendously with habitat type.
Specialized sampling techniques have been developed for insects that live in the soil, in the air, on foliage, and on vertebrate hosts. A large scientific literature exists on the methods developed for each of these habitats.
One can make several general distinctions about different methods of sampling insects.
Most insects are maintained at very low population levels by "natural control" and are not viewed as pest species. Only 10, to 30, of the one million insect species known are pests. These pests feed on crops, forests, pasture lands, or livestock or menance our health, comfort or possessions. A commonly used technique to estimate the population density is based on the mark-release-recapture method (e.g. Seber, ), which is effective in scientific studies but is impractical for the purposes of pest monitoring where the number of traps per unit area is usually small and release of pest insects can hardly be justified. POPULATION DYNAMICS OF MAJOR INSECT PESTS OF COTTON IN RELATION TO ABIOTIC FACTORS Sadre Alam Fakhri, M. and Khowaja Jamal Department of Zoology, Aligarh Muslim University, Aligarh (India) pest population in the high density crop could mainly be.
One of these is to distinguish between absolute and relative measures of density. Absolute measures quantify numbers per unit area or volume of habitat. Examples are numbers of grasshoppers per square meter in quadrat samples or numbers of Collembola per cubic centimeter of soil. Relative measures express numbers per sample unit, such as numbers of insects captured in a sweep-net sample or numbers of male moths captured in pheromone-baited traps.
Relative measures may or may not reflect absolute density. They are frequently much easier to obtain than absolute measures, but they may be influenced by many factors e.
Consequently, much research is needed to be sure that relative measures give an accurate indication of differences in absolute population density.
In addition, there are population indices, which are indirect measures of density, such as measures of defoliation. Examples of the latter include sweep-net samples, quadrat samples, and insecticide knockdown samples.
Such instantaneous samples are susceptible to the effects of time of day or weather conditions at the time of sampling, which in turn may influence the number captured.
Continuous samples may also be influenced by weather conditions but, because capturing occurs over an extended interval, these effects are averaged over a range of such conditions. Any investigator planning a sampling program must think carefully about how the samples will be selected.
Consultations with statisticians with expertise in experimental design prior to collection of data is always wise, as is preliminary sampling or pilot testing to estimate the expected amount of sample variability.
Most sampling schemes may be classified as random, systematic, or stratified random designs.
In random sampling, the sample units are chosen or placed at randomly selected locations in the sample area. Random selection is typically done by choosing coordinate points from a table or list of random numbers. In a systematic design, sample units are placed at regular intervals across the sample universe e.
Systematic samples are frequently much easier to conduct, and they ensure that the samples are distributed evenly across the sample universe. However, systematic samples violate the requirement that samples be selected independently and at random from the sample universe, imposed by most statistical analyses.
Whether violation of this requirement leads to erroneous conclusions in any particular system is usually debatable. A reasonable compromise between the two approaches is a stratified random or randomized block design in which the sample universe is divided into regularly spaced subunits or blocks and samples are selected at random from each block.
Differences in density between subunits caused by edge effects or density gradients across the field can be detected with appropriate statistical analysis. Mark-recapture techniques are sometimes used to estimate insect abundance. Individuals are marked with a permanent mark that does not significantly alter the behavior of the insect or affect its survival.
Marked individuals are counted and released into a population. If one assumes that M, the number of marked individuals in the population, is equal to the number released, then the population size N can be calculated directly: This calculation is known as the Lincoln index or Peterson estimate.
As a rule, it cannot be assumed that M is equal to the number of marked individuals released because some of them will have died or emigrated in the interval between release and recapture.
Several fairly elaborate techniques involving multiple rounds of mark and recapture have been developed to estimate M when it is unknown.POPULATION DYNAMICS OF MAJOR INSECT PESTS OF COTTON IN RELATION TO ABIOTIC FACTORS Sadre Alam Fakhri, M. and Khowaja Jamal Department of Zoology, Aligarh Muslim University, Aligarh (India) pest population in the high density crop could mainly be.
Population Density of Major Insect Pest as Influenced by Spatial Arrangement in Pechay Words | 7 Pages population density of major insect pest as influenced by spatial arrangement in pechay by ABSTRACT Spatial arrangement in pechay production could be used as an strategic pest management.
Population ecology deals with questions related to the density or number of individuals of a species in a habitat or location. Insect population ecologists try to understand why population densities of some insects fluctuate dramatically, but others show little variation in .
In view of this, adequate information is very important on population density of insect pests associated with watermelon in southern guinea savanna agro ecological zone, Ogbomoso.
based on this it was ranked as the second major insect during the late planting season. The least population density of Z.
insects could have an important effect on plant popUlation dynamics. The flaws in these arguments are numerous and have been discussed elsewhere (36, 62, ). Effect of plant trapping on the population density of soybean insect pests Soybean, G.
max seeds (variety Crawford; obtained from the Field Crops Research Institute, M.O.A.) were sown during the first week of May in and seasons.