摘要:

A simulation model (REPO–PERM) was developed to predict the rate of resistance development in Colorado potato beetle,Leptinotarsa decemlineata(Say), using field data on permethrin selection to initialize a number of ecological and genetic parameter values. Model explorations indicated that sex–linked traits, like permethrin resistance in Colorado potato beetle, respond to directional selection faster than autosomal traits, and that the distribution of individuals in the plant canopy can influence selection intensity and the rate of adaptation. Model predictions for rates of adaptation to permethrin under conditions typical of Virginia and North Carolina are consistent with documented development of resistance in these areas.

ISSN:1754-5692    

DOI:10.1093/ee/24.2.167

出版商:Oxford University Press    

年代:1995

数据来源: OUP

摘要:

In paired–choice assays, two treatments are presented simultaneously to each subject. Data from such arrays should not be considered to be independent, and correct statistical analysis must account for the correlation. A statistical test that often is appropriate for these assays is the paired–samplet–test. I present curves showing the extent to which statistical power of this test is affected by sample size, effect size (i.e., magnitude of treatment differences), and correlation. For a given effect size and replication, positive correlation between paired observations substantially improves power of the test, whereas negative correlation reduces power. I conducted a literature survey of paired–choice assays to determine whether there are patterns in effect sizes and correlation that might assist in designing studies or in predicting minimum sample sizes necessary to achieve reasonable statistical power; experiments were categorized according to whether they were feeding or oviposition assays. The review indicated that correlation was highly variable and ranged between strongly negative and strongly positive values. Oviposition assays showed larger positive correlations than did feeding assays, resulting in larger effect sizes (adjusted for correlation); however, feeding assays tended to use larger sample sizes than oviposition assays, hence estimated statistical power was similar between the two types of assays. Oviposition assays often used multiple insects per arena, apparently sacrificing replication, whereas feeding assays tended to use a single insect per arena. Approximately 45% of experiments failed to detect significant treatment effects. The majority of nonsignificant assays had too few replications to detect even a large effect size with a reasonable statistical power. Literature examples are presented to show that assay methodology (specifically number of insects per arena, distance between paired choices, and assay duration) can affect correlation, effect size, and statistical power. Finally, scatter plots of the data, although rarely presented, are shown to provide insight into methodological, statistical, and biological aspects of paired–choice assays.

ISSN:1754-5692    

DOI:10.1093/ee/24.2.179

出版商:Oxford University Press    

年代:1995

数据来源: OUP

摘要:

Three different gypsy moth,Lymantria dispar(L.), sampling techniques were compared for their spatial correlation with regional defoliation maps. Counts of gypsy moth pupae and egg masses under burlap bands, and counts of male moths in pheromone–baited traps were taken in a network of 150 plots distributed irregularly throughout Massachusetts. These counts were compared with aerial sketch maps of gypsy moth defoliation collected during the same period and digitized into cells (2 by 2 km) cells in a geographic information system. The spatial correlation between counts of the three gypsy moth life stages and defoliation was examined using indicator cross–correlograms. A cross–correlogram quantifies the spatial covariation between two variables by plotting the cross–correlation for a series of interpoint distances. Cross–correlograms indicated that there was substantial correlation between egg mass counts and subsequent defoliation. These correlations extended to 10 cells (20 km) in some cases. Similar patterns were observed for counts of pupae. In contrast, there was little cross–correlation between defoliation and counts of male moths. These results indicate that counts of egg masses (or pupae) under burlap bands may be the most suitable variable to measure for predicting gypsy moth defoliation on a regional scale. The lack of correlation between male moth counts and regional defoliation is discussed.

ISSN:1754-5692    

DOI:10.1093/ee/24.2.193

出版商:Oxford University Press    

年代:1995

数据来源: OUP

摘要:

A sampling plan to estimate population levels ofLiriomyza huidobrensis(Blanchard) larvae and total mining damage was developed for use in celery. Dispersion indices from Taylor's power law were calculated from 1992 data obtained from whole plant samples collected from commercial fields at two times during the cropping season and utilizing one of three different leafminer management strategies. Analysis of covariance indicated that variance–to–mean relationships were consistent among petiole position among plants, pest management strategies, and time of growing season for liveL. huidobrensislarvae and total numbers of mines per petiole. In an attempt to develop a presence–absence sampling plan, all equation was derived to relate the proportion of petioles infested,P(l), to the mean number of live larvae or the mean number of mines per petiole. However, predicted frequencies of infested petioles delivered from this equation were significantly greater than the frequencies of petioles infested with live larvae or infested with mines observed in validation studies. This lack of fit between predicted and expected frequencies precludes use of a presence–absence sampling plan to predict mean densities from the proportion of leaves infested. The results from Taylor's dispersion analysis were also used to evaluate a constant precision–level sampling plan. Validation tests of this sampling plan indicated that the formula used to ca1culate critical stoplines accurately predicted the observed cumulative totals of live larvae or total numbers of mines. Implementation of a sequential sampling plan forL. huidobrensislarvae with a 0.25 level of precision and with a possible maximum sample size of 100 petioles (to compensate for the prohibitively large sample sizes necessary at low densities) should greatly reduce the amount of labor necessary to achieve accurate estimates of population densities and to facilitate the use of action thresholds based upon these estimates.

ISSN:1754-5692    

DOI:10.1093/ee/24.2.204

出版商:Oxford University Press    

年代:1995

数据来源: OUP

摘要:

A rangeland grasshopper model (HopMod) was developed to incorporate phenological development, forage destruction, natural mortality, and control option efficacy (of the current registered treatments) for a a complex of rangeland grasshopper species. These factors must be considered to make economically based management decisions for rangeland grasshoppers. The phenology component is based on heat accumulation for populations under field conditions. Phenology parameters were developed directly from field data from Montana over many sites and years for the species complexes of interest. In addition, HopMod phenology and density can be initialized with real–time field data to improve accuracy. Therefore, the model has potential application over broad geographic areas where similar species complexes occur. This is important because it is very expensive and impractical to collect data necessary to develop site–specific models over such large areas in the western United States. In addition to phenology, there are components to simulate forage consumption, oviposition, natural mortality, and control mortality (including chemical and biological control). The population dynamics component was validated with field data from western North Dakota. Forage consumption was verified by comparing HopMod with previously described methods to estimate grasshopper forage consumption. HopMod was designed to run on a microcomputer (MS–DOS, written in Borland Pascal) as part of a larger decision support system, but can also run as a stand–alone program. The decision support system uses results from HopMod to determine economic utility of treatments suggested by an expert system.

ISSN:1754-5692    

DOI:10.1093/ee/24.2.212

出版商:Oxford University Press    

年代:1995

数据来源: OUP

摘要:

Spider mite outbreaks following the application of insecticides have been associated with changes in mite dispersal behavior. Dispersal responses of twospotted spider mite,Tetranychus urticaeKoch, and Banks grass mite,Oligonychus pratensis(Banks), were studied when mites were exposed to various sublethal concentrations of insecticides on maize under laboratory conditions. Insecticides tested were formulated materials of permethrin and methyl parathion. The study was conducted under direct exposure of mites to pesticides and exposure to their residues. Mites showed greater dispersal behavior when exposed to pesticides directly compared with residual exposure. Spin–down was the predominant mode of dispersal when mites were exposed to insecticides directly, whereas mites that were exposed to the residues dispersed mainly by walk–off. An increase in dispersal of both species of spider mites was observed as concentrations of insecticides increased from LC50to LC50. At LC50, methyl parathion caused greater dispersal of Banks grass mites compared with twospotted spider mites by both direct and indirect exposure. In contrast, at LC50permethrin caused greater dispersal of twospotted spider mites compared with Banks grass mites by both conditions of exposure.

ISSN:1754-5692    

DOI:10.1093/ee/24.2.226

出版商:Oxford University Press    

年代:1995

数据来源: OUP

摘要:

Within–tree distribution of pear thrips,Taeniothrips inconsequens(Uzel), in Sugar maple,Acer saccharumMarsh., was determined in six nonflowering trees in 1990 and six flowering trees in 1992. During budburst, vegetative (1990) and flower (1992) buds were sampled from four cardinal quadrants, two canopy positions (inside and outside), and three crown levels (upper, middle, and lower) of sugar maples in a plantation in central Pennsylvania and examined for thrips eggs and adults. Almost all thrips adults were identified asT. inconsequens(94.9% in 1990 and 97.0% in 1992) and all eggs were likely to be fromT. inconsequensbecause of their position in bud tissues and their morphology. Few larvae were present. Thrips eggs and adults were found in vegetative and flower buds throughout all levels, positions and quadrants. There were few significant differences in relation to any part of the tree in either year. In 1990 significantly more eggs (but not adults) were found in the middle level, compared with the lower and the upper levels. There was a significant interaction between height and quadrant for eggs (but not adults) in 1992. Within–tree distribution of pear thrips is likely to be affected by the synchrony between thrips emergence from ovelwintering sites and the timing of budburst in a particular position within the tree, and the distribution and density of flowers.

ISSN:1754-5692    

DOI:10.1093/ee/24.2.233

出版商:Oxford University Press    

年代:1995

数据来源: OUP

摘要:

The objective of this study was to examine the effects of theB. thuringiensisbased MVP biopesticide on the development of baculoviruses inSpodopteralarvae. The sensitivity of both the beet armyworm,Spodoptera exigua(Hübner) and the fall armyworm,S. frugiperda(J. E. Smith), to the CryIA(c) toxin present in MVP was temporary; upon reaching the third instar, both species were much less susceptible to the CryIA(c) toxin. The sublethal effects of MVP onSpodoptera, reflected by a delay in larvae development, did not alter the dose response of these insects to their respective nuclearpolyhedrosisvirus. However, feeding the virus infected Spodoptera larvae MVP amended diet (10 mg/ml) did increase the number of second instars succumbing to virus infection. Microscopic examination of the larva killed by the MVP baculovirus demonstrated normal virus inclusion formation. In snmmary, onr laboratory bioassays suggested thatB. thuringiensisdelta endotoxins, applied at rates that are sublethal, should not interfere with baculovirus development inB. thuringiensistolerant hosts such asS. exiguaandS. frugiperda.

ISSN:1754-5692    

DOI:10.1093/ee/24.2.239

出版商:Oxford University Press    

年代:1995

数据来源: OUP

摘要:

We used the spatial distribution of white grubs in 100 observations to simulate, in a computer program, the potential mortality caused by 221 different hole patterns of commercial turfgrass aerators. Hole patterns arranged in a distribution (5.08–cm × 5.08–cm) with tine diameters of 2.54 and 1.90 cm were able to produce a grub mortality of>40%. The efficiency of these designs, as measured by the overall percentage of mortality under moderate and light grub infestation was considerably high. The results also show that the percentage area made by aerator holes is not directly proportional to mortality; the distribution of holes is as important as the area affected by them. The use of turfgrass aerators with appropriate hole patterns can reduce subterranean pest populations to manageable levels and should be considered in integrated pest management programs.

ISSN:1754-5692    

DOI:10.1093/ee/24.2.243

出版商:Oxford University Press    

年代:1995

数据来源: OUP

摘要:

Soil arthropod communities were surveyed and compared in litter layers of selectively harvested and nonharvested forests of coast redwood,Sequoia sempervirens, to assess impact of a l5-yr selective timber harvest cycle. Abundance of four guilds (microphytophages, panphytophages, macrophytophages, and predators) were estimated from litter samples taken from three forest classes: uncut old growth, mature second growth last harvested before 1920, and selectively harvested forest sampled 14 yr after harvest. Microphytophage and panphytophage abundance did not vary significantly among forest classes. Macrophytophages showed significantly higher abundance in selectively harvested forest, whereas predators showed significantly reduced abundance in selectively harvested forest. Because no significant differences in macrophytophage and predator abundance were found between old growth and mature second growth classes, observed differences are attributed to the selective timber harvest regime. Furthermore, since selectively harvested forest was sampled for arthropods 14 yr after harvest, it appears that the 15-yr cycle is of insufficient duration to allow full recovery of soil arthropod communities from the effect of selective timber harvest. In addition, it is likely that species are at high risk of extinction, based on the striking observation that an entire order, Diplura, was absent from all samples taken from selectively harvested sites. Possible explanations for observed differences in guild abundance and potential implications for long-term maintenance of soil arthropod diversity are discussed.

ISSN:1754-5692    

DOI:10.1093/ee/24.2.246

出版商:Oxford University Press    

年代:1995

数据来源: OUP