The making of a pest: recruitment of Meligethes aeneus onto oilseed Brassicas

Populations of the rapeseed pollen beetle Meligethes aeneus F. (Col., Nitidulidae) from areas with 0–16 years of history of intensive rapeseed growing were compared for key ecological characters. During the first 16 years of rapeseed cultivation the reproductive success of M. aeneus increased 200–300% over that of the beetles living on the natural host plants, cruciferous weeds. The increase was linear over time and statistically highly significant, and it did not appear to be related to food quality or to the size of the beetles. During the same period the tolerance to intraspecific competition decreased, possibly due to the relative absence of such competition on the new crop. Furthermore, the optimum population density for M. aeneus to maximize the size of its next generation on summer turnip rape was determined to be 0.5–1.0 beetles/plant, which is slightly below the economic threshold for chemical control (1 beetle/plant). Therefore the practical protection of the rapeseed yield also ensures the highest possible pest population size for the next year. These mechanisms may in part explain the particular noxiousness of the species as a pest all over Europe. In general these data show that after the introduction of a new crop plant into a region, significant changes during the recruitment process in a pestiferous insect may take place, contributing to the future pest status of the insect. It is suggested that such genetic and ecological changes in insects may be a more common mechanism than previously thought in initiating and sustaining pest outbreaks, and that conventional pest management methods may enhance that effect.     

高原鼠兔种群恢复过程中的洞穴分布动态

高原鼠兔洞穴系统的恢复是其种群恢复的关键指标之一,洞穴分布的变化可以反映种群的动态。本研究于2014-2016年在青海省祁连县对2.79 hm2高寒草甸内高原鼠兔(Ochotona curzoniae)种群密度、洞穴密度和洞穴的相对位置进行跟踪观测。其中包括6个50m×50m 的灭鼠堵洞处理、6个30m×30m 的灭鼠处理和3个50m×50m的对照处理。分别采用平均最近邻指数和平均拥挤度指数分析洞穴系统中有效洞、弃洞、粪坑和嬉戏坑的分布模式及洞系表现面积,并对各参数进行描述性和相关性分析。结果显示：高原鼠兔种群密度恢复过程中（1）有效洞的空间格局由随机向离散分布转变,弃洞由随机向聚集分布转变,粪坑和嬉戏坑无明显变化趋势;有效洞和弃洞分布格局的恢复都朝向灭鼠前状态,但恢复的都不充分;（2）有效洞最近邻指数与其自身密度正相关;弃洞最邻近指数与其自身密度负相关;粪坑、嬉戏坑最近邻指数与其自身密度无显著相关性;其中,仅粪坑的分布最近邻指数与高原鼠兔种群密度呈显著负相关;（3）有效洞与粪坑、嬉戏坑表现面积的变化情况较为一致,与弃洞呈互补态势;洞系表现面积的变异性远小于洞穴密度。结果说明：（1）高原鼠兔洞穴分布格局和洞穴密度的恢复具有滞后性;（2）有效洞、弃洞的分布格局主要受洞穴密度的影响;（3）高原鼠兔种群的恢复过程中对洞系面积的需求优先于洞口数量。     

大尺度下褐飞虱种群空间结构初步分析

褐飞虱是我国主要的水稻害虫,有着复杂的空间结构.地统计学可用来分析空间相关变量的结构和插值模拟空间相关变量的分布.运用地统计学中的变差函数和克立格插值法对广东省褐飞虱种群3个主要世代在早稻田间的空间结构进行分析和模拟的结果表明,大尺度的褐飞虱田间种群的空间分布为聚集型,不同世代褐飞虱种群的局部空间结构有差异,聚集的范围分别为400、200和205km;空间分布模拟地图能反映褐飞虱种群在田间的具体分布情况,广东西部地区每一世代褐飞虱的发生密度均高于东部地区.     

大尺度下褐飞属种群空间结构初步分析

褐飞虱是我国主要的水稻害虫,有着复杂的空间结构,地统计学可用来分析空间相关变量的结构和插植模拟空间相关变量的分布,运用地统计学中的变差函数和克立格插值法对广东省褐飞虱种群3个主要世代在早稻田间的空间结构进行分析和模拟的结果表明,大尺度的褐飞虱田间种群的空间分布为聚集型,不同世代群在田间的具体分布情况,广东西部地区第一世代褐飞虱的发生密度均高于东部地区。     

A model descriptive of gregariousness of colonial insect larvae

A model is constructed to describe gregariousness of colonial insect larvae which occure in discrete natural habitat units. The model is based on the assumption that the distribution of individuals in a clump is determined by a balance between aggregative and dispersing movements of individuals. The model includes three parameters, i.e., clump size, carrying capacity of habitat units and intensity of aggregation against dispersal. The modes of effects of these parameters on the distribution of individuals are analyzed. Several methods are developed to estimate these parameters from observed data, and their applicabilities are investigated. Application of these methods are described on the larval distribution of a colonial insect Pryeria sinicaMoore .     

Characterization of western corn rootworm (Coleoptera: Chrysomelidae) population dynamics in relation to landscape attributes

Abstract 1 The western corn rootworm (WCR), Diabrotica virgifera virgifera Leconte (Coleoptera: Chrysomelidae), creates economic and environmental concerns in the Corn Belt region of the U.S.A. To supplement the population control tactics of the Areawide Pest Management Program in Brookings, South Dakota, Geographical Information Systems (GIS) were used to examine the spatial relationships from 1997 to 2001 between WCR population dynamics, habitat structure, soil texture and elevation. 2 Using the inverse distance weighted interpolation technique, WCR population density maps were created from georeferenced emergence and post‐emergence traps placed in maize fields. For each year, these maps were overlaid with vegetation, soil and elevation maps to search for quantitative relationships. 3 Through visual interpretation and correlation analysis, shifts in landscape structure, such as size, number and arrangement of patches, were shown to associate with WCR population abundance and distribution in varying degrees. Contingency analysis showed that WCR population abundance is associated with soil texture and elevation. 4 An understanding of the interactions between WCR population dynamics and landscape variables provides information to pest managers, and this can be used to identify patterns in the landscape that promote high insect population density patches to improve pest management strategies.     

Biological Control of the Cassava Mealybug in Africa: A Review

Among several natural enemies introduced to combat the cassava mealybug, Phenacoccus manihoti (Homoptera: Pseudococcidae), the neotropical parasitoid Apoanagyrus (Epidinocarsis) lopezi (Hymenoptera: Encyrtidae) was the most successful. It established in 26 African countries, causing a satisfactory reduction in the population density of P. manihoti in most farmers' fields. Four conclusions concerning the possible application of the research results to other biological control projects are discussed. (1) Foreign exploration was intensive and should be maintained at this level in other projects, if necessary at the cost of other activities. (2) In the controversy about the amount of research results needed before first releases are made, an understanding of the proper role of quarantine is essential. Whereas quarantine (preferably outside the continent) guarantees nonnoxiousness of natural enemies, only research in the experimental release sites can determine whether a given natural enemy will be efficient. It was confirmed that the released exotic insects did not affect the diversity of the indigenous fauna. Modalities used in this project for the execution of releases, i.e., always on request by and in collaboration with national programs, are recommended for adoption in future projects. (3) Laboratory and field studies established the scientific basis for quantifying the impact of the pest insect and its control by A. lopezi. This was expressed as reduction in pest population levels and yield loss and gain in revenue. Behavior of adult females in searching and choosing hosts was identified as a better predictor of efficiency of a species in the field than life table studies under controlled temperatures. (4) It is concluded that biological control is the basis for integrated pest management. Other interventions, such as cultural methods or the use of resistant varieties, need to be in harmony with biological control because the impact of natural enemies cannot usually be manipulated by the farmer. To achieve sustainability, the aim is to optimize tritrophic interactions among the plant, the phytophagous pest organisms, and their natural enemies, rather than to maximize the effect of a single intervention.     

Vertical stratification in the spatial distribution of the beech scale insect (Ultracoelostoma assimile) in Nothofagus tree canopies in New Zealand

Abstract. 1. The degree of infestation by New Zealand sooty beech scale insects (Ultracoelostoma assimile, Homoptera: Margarodidae) varies dramatically among adjacent southern beech trees (Nothofagus spp., Fagaceae), but has previously been assumed to be uniformly or randomly distributed within individual host trees. In this study, a full‐census survey was conducted from ground level to canopy level on 14 naturally occurring, canopy‐dominant red beech (Nothofagus fusca) trees (size range 38.7–107.6 cm diameter at breast height) to determine the degree of within‐tree heterogeneity in herbivore density. 2. The within‐tree distribution of the sooty beech scale was vertically stratified and highly heterogeneous, with the greatest densities occurring on bark surfaces in the canopy rather than on the trunk, and on the lower rather than upper sides of the branches. The spatial distribution was strongly negatively correlated with trunk and branch diameter, and increasing bark thickness (as a function of diameter) provides a plausible explanation for differences in the establishment and population density of sooty beech scale insects with trunk and branch size. Furthermore, there was a significant change in the spatial distribution of scale insect populations on trunks and branches of trees of increasing diameter at breast height. This indicates a strong temporal component to the spatial dynamics of the sooty beech scale insect driven by changing host phenology. Future studies on phytophagous insects infesting large host trees need to consider more explicitly changes in population dynamics through space and time. 3. Because of the high degree of within‐tree heterogeneity in population density, the total population size of scale insects on an individual tree could not be predicted from any measure of population density low on the trunk. However, the dry weight biomass of sooty mould fungi growing on the ground beneath infested trees was a remarkably accurate predictor of the total population size of scale insects. The use of sooty mould fungi as a relative measure of population size could be incorporated into studies of other honeydew‐producing hemipterans, since the growth of sooty mould is a distinctive feature synonymous with high concentrations of honeydew production worldwide.     

Release of genetically engineered insects: a framework to identify potential ecological effects

Genetically engineered (GE) insects have the potential to radically change pest management worldwide. With recent approvals of GE insect releases, there is a need for a synthesized framework to evaluate their potential ecological and evolutionary effects. The effects may occur in two phases: a transitory phase when the focal population changes in density, and a steady state phase when it reaches a new, constant density. We review potential effects of a rapid change in insect density related to population outbreaks, biological control, invasive species, and other GE organisms to identify a comprehensive list of potential ecological and evolutionary effects of GE insect releases. We apply this framework to the Anopheles gambiae mosquito – a malaria vector being engineered to suppress the wild mosquito population – to identify effects that may occur during the transitory and steady state phases after release. Our methodology reveals many potential effects in each phase, perhaps most notably those dealing with immunity in the transitory phase, and with pathogen and vector evolution in the steady state phase. Importantly, this framework identifies knowledge gaps in mosquito ecology. Identifying effects in the transitory and steady state phases allows more rigorous identification of the potential ecological effects of GE insect release.     

On numerical uncertainty in evaluation of pest population size

Obtaining reliable estimates of pest insect species abundance is an essential part of ecological monitoring programs. It is often the case that data available for obtaining such estimates are sparse which in turn makes achieving an accurate evaluation difficult. This is especially true for strongly heterogeneous pest population density distributions. In our paper we discuss the accuracy of a mean density estimate when a certain class of high aggregation density distributions is considered and a standard statistical method is employed to handle sparse sampled data. It will be shown in the paper that conventional conclusions about the accuracy of the pest population size evaluation do not work when the data are sparse and a new approach is required. Namely, if the number of traps is small, an estimate of the mean density becomes a random variable with an error of high magnitude and we have to compute the probability of an accurate estimate rather than computing the estimate itself. We have obtained a probability of an accurate estimate based on the assumption that only one trap falls within a sub-domain where the pest population density is different from zero. The probability has been calculated for the one-dimensional and the two-dimensional problem.     

The utility of microsatellite DNA markers for the evaluation of area-wide integrated pest management using SIT for the fruit fly, Bactrocera dorsalis (Hendel), control programs in Thailand

The oriental fruit fly, Bactrocera dorsalis (Hendel), is a key pest that causes reduction of the crop yield within the international fruit market. Fruit flies have been suppressed by two Area-Wide Integrated Pest Management programs in Thailand using Sterile Insect Technique (AW-IPM-SIT) since the late 1980s and the early 2000s. The projects’ planning and evaluation usually rely on information from pest status, distribution, and fruit infestation. However, the collected data sometimes does not provide enough detail to answer management queries and public concerns, such as the long term sterilization efficacy of the released fruit fly, skepticism about insect migration or gene flow across the buffer zone, and the re-colonisation possibility of the fruit fly population within the core area. Established microsatellite DNA markers were used to generate population genetic data for the analysis of the fruit fly sampling from several control areas, and non-target areas, as well as the mass-rearing facility. The results suggested limited gene flow (m < 0.100) across the buffer zones between the flies in the control areas and flies captured outside. In addition, no genetic admixture was revealed from the mass-reared colony flies from the flies within the control area, which supports the effectiveness of SIT. The control pests were suppressed to low density and showed weak bottleneck footprints although they still acquired a high degree of genetic variation. Potential pest resurgence from fragmented micro-habitats in mixed fruit orchards rather than pest incursion across the buffer zone has been proposed. Therefore, a suitable pest control effort, such as the SIT program, should concentrate on the hidden refuges within the target area.     

Landscape refuges delay resistance of the European corn borer to Bt-maize: a demo-genetic dynamic model

We constructed a reaction-diffusion model of the development of resistance to transgenic insecticidal Bt crops in pest populations. Kostitzin’s demo-genetic model describes local interactions between three competing pest genotypes with alleles conferring resistance or susceptibility to transgenic plants, the spatial spread of insects being modelled by diffusion. This new approach makes it possible to combine a spatial demographic model of population dynamics with classical genetic theory. We used this model to examine the effects of pest dispersal and of the size and shape of the refuge on the efficiency of the “high-dose/refuge” strategy, which was designed to prevent the development of resistance in populations of insect pests, such as the European corn borer, Ostrinia nubilalis Hübner (Lepidoptera, Crambidae). We found that, with realistic combinations of refuge size and pest dispersal, the development of resistance could be considerably delayed. With a small to medium-sized farming area, contiguous refuge plots are more efficient than a larger number of smaller refuge patches. We also show that the formal coupling of classical Fisher–Haldane–Wright population genetics equations with diffusion terms inaccurately describes the development of resistance in a spatially heterogeneous pest population, notably overestimating the speed with which Bt resistance is selected in populations of pests targeted by Bt crops.     

Measuring Home-Range Changes Following Density Reduction of Australian Brushtail Possum

It is not clear whether animals consistently change their home ranges in response to density reduction. This is important to understand for better management of pest species where sustained control is required. Our objective was to measure whether home ranges of Australian brushtail possums (Trichosurus vulpecula) change following density reduction, using global positioning system (GPS) tracking. We experimentally reduced the densities of 2 populations (1 high-density at 7 possums/ha and 1 low-density at 1.5 possums/ha) and did not manipulate another population. We then monitored home ranges of individual possums. The high-density manipulated population had a significant increase in home-range size and overlap within 5 weeks following reduction, whereas the other 2 populations did not. This research suggests that changes in possum home ranges following control are likely influenced by the initial density of the pest population. © 2019 The Wildlife Society.     

Landscape features and spatial distribution of adult northern corn rootworm (Coleoptera: Chrysomelidae) in the South Dakota areawide management site

The northern corn rootworm, Diabrotica barberi Smith & Lawrence (Coleoptera: Chrysomelidae), creates economic and environmental concerns in the Corn Belt. To supplement the population control tactics of the Areawide Pest Management Program in Brookings, SD, geographic information systems were used from 1997 to 2001 to examine the spatial relationships between D. barberi population dynamics and habitat structure, soil texture, and elevation. Using the inverse distance weighted interpolation technique, D. barberi population density maps were created from georeferenced emergence and postemergence traps placed in maize, Zea mays L., fields. For each year, these maps were overlaid with vegetation, soil, and elevation maps to search for quantitative relationships between pest numbers and landscape structure. Through visual interpretation and correlation analysis, shifts in landscape structure, such as size, number, and arrangement of patches were shown to associate with D. barberi population abundance and distribution in varying degrees. D. barberi were found in greater proportions than expected on loam and silty clay loam soils and on elevations between 500 and 509 m. An understanding of the interactions between D. barberi population dynamics and landscape variables provides information to pest managers, which can be used to identify patterns in the landscape that promote high insect population density patches to improve pest management strategies.     

Larger wildflower plantings increase natural enemy density,diversity, and biological control of sentinel prey,without increasing herbivore density

1. An important means of conserving beneficial insects in resource‐limited habitats is to meet their ecological requirements, which may be achieved by providing areas containing flowering plants that bloom throughout the season, but little is known about the importance of wildflower plot size for supporting natural enemies or the biological control they provide. 2. Wildflowers were established in plots of sizes ranging from 1 to 100 m², and found that natural enemy density, group richness, and diversity of natural enemy groups increased with plot size. 3. The density of insect herbivores was lower in all flower plots than in the control samples, whereas the diversity of herbivore groups was significantly higher in flower plots. 4. Comparing population growth of sentinel soybean aphids (Aphis glycines Matsumura) among plot sizes, aphid colonies were smaller as plot size increased. 5. Providing beneficial insects with flowering resources resulted in significantly more natural enemies and greater pest control than in smaller flower plots or mown grass areas. 6. These results indicate that the density, diversity, and function of natural enemies are sensitive to the size of wildflower plantings, even at relatively small scales. Therefore, larger wildflower plots are more suitable for the conservation of beneficial insects and their provision of natural pest control.     

温度对昆虫繁殖力的影响及其生理生化机制

生殖是昆虫维持种群繁衍的基本生命活动,温度是重要的影响因素之一。温度偏离正常生长温度会影响昆虫性腺发育和能量代谢,从而导致昆虫生殖生理异常,具体表现为产卵数降低、性比偏移、产卵前期变化、孵化率降低等。温度影响昆虫繁殖可能的生化与分子机制主要有性外激素、蜕皮激素、保幼激素及其他内分泌神经肽和热激蛋白等的参与,但该方面的研究尚处在初步探索阶段,多不成系统,需要进一步深入。研究温度对于昆虫繁殖力的影响对害虫爆发预测具有重要作用,可为害虫防治提供新思路;而且研究温度对繁殖力的影响可以预测在全球变暖的背景下昆虫种群密度的新变化和新分布情况,为全球生态系统的动态变化提供参考。     

Theory,Technology, and Practice of Site-Specific Insect Pest Management

Insects are usually unevenly distributed throughout an area in nature. Despite this knowledge, analytical methods and technology have limited insect pest management to uniform management decisions in the field. Recently, the methods and technology to map and analyze insect spatial distribution have been developed to a level where the uneven nature of insect populations can be considered for application of pest management tactics. This new approach to insect management is termed site-specific pest management. Site-specific pest management utilizes spatial information about pest distribution to apply control tactics only where pest density is economically high within a field. This review will detail the current status of site-specific insect pest management in agriculture, technological requirements, its limitations, and future potential.     

Distribution of Insect Attacks in Biological Control of Weeds: Infestation of Centaurea virgata Flowerheads by a Gall Fly

The success of biological control efforts to reduce weed density through release of insects may depend as much on the distribution of insect attacks among individual plants or plant parts as on the mean level of infestation. We used an index of dispersion to describe the distribution of Urophora quadrifasciata (Diptera: Tephritidae) galls among squarrose knapweed (Centaurea virgata) flowerheads at 18 west central Utah sites in the first 5 years following introduction of the biological control agent. Two thirds of the samples showed a significantly aggregated distribution of galls among flowerheads. Statistical analysis showed that site and year accounted for relatively small proportions of the variance in the index of dispersion. The degree of gall aggregation among flowerheads was positively correlated with the mean flowerhead quality (mean number of seeds per flowerhead; P = 0.013) and tended to be negatively correlated with the mean fly density per flowerhead at a site in a given year (P = 0.097). Our data suggest that higher quality flowerheads, and possibly higher quality plants, are preferentially attacked by U. quadrifasciata and therefore are more heavily subject to reduced reproductive potential through biological control. However, an aggregated distribution of fly attacks may undercut the potential of the fly to reduce seed production by the weed population as a whole. Understanding both the distribution of insect attacks among individual plants and the behavioral mechanisms producing such distribution patterns is important to the biological control of weeds.     

Clump size selection: A field test with two species of Dipodomys

Summary Seed distribution (clump size) selection has been proposed as a possible mechanism of resource subdivision for competing heteromyid rodent species. To test this hypothesis, field experiments were conducted over two years during both richer and sparser seasons of the year. None of the predictions derived from the hypothesis were supported by our results. Though some selectivity was displayed by both Dipodomys spectabilis and D. merriami, the patterns of selectivity did not match the expected patterns. Our results further indicate that clump selection may be influenced by variables other than the density of seeds within a clump. These results have led us to conclude that clump size selection is unlikely to play a role in the coexistence of different species of the genus Dipodomys.     

Habitat heterogeneity affects predation of European pine sawfly cocoons

Habitat heterogeneity is thought to affect top‐down control of herbivorous insects and contribute to population stability by providing a more attractive microhabitat for natural enemies, potentially leading to reduced population fluctuations. Identifying the parameters that contribute to habitat heterogeneity promoting top‐down control of herbivorous insects by natural enemies could facilitate appropriate management decisions, resulting in a decreased risk of pest insect outbreaks because of a higher level of predation. In our study, we measured the top‐down pressure exerted by small mammals on the cocoons of a notorious pest insect in pine forests, the European pine sawfly (Neodiprion sertifer), which is known to be regulated by small mammal predation. The forest stands used differed in heterogeneity measured in terms of differences in tree diversity and density, understory vegetation height, presence/absence, and density of dead wood. We found higher predation in more dense spots within forest stands. Further, the effect of dead wood on sawfly cocoon predation depended on the pine proportion in forest stands. The addition of dead wood in a manipulation experiment had a slight positive effect on cocoon predation, while dead wood removal caused a clear decrease in predation rate, and the decrease was more pronounced when the proportion of pine increased. Our results show that habitat heterogeneity affects predation by generalist predators on herbivorous insects. This knowledge could be applied to reduce the risk of insect outbreaks by applying management methods that increase heterogeneity in perennial systems such as forests and orchards, thus decreasing the levels of insect damage.