Effects of host density and instar stage on mass-rearing efficiency of Microplitis manilae (Hymenoptera: Braconidae)

Effects of host density and plant species diversity on populations of Colorado potato beetle, Leptinotarsa decemlineata (Say), were studied in experimental field plots. Hosts were grown at two densities and four levels of plant diversity: potato monoculture, potato/bean biculture, potato/bean/weed triculture, and potatoes grown in fallow plots. All life stages of the beetle were affected by both host density and plant diversity. Numbers of beetles per plant were highest in low-diversity cultures of low host density; higher host density or plant diversity was accompanied by a reduction in numbers of beetles per plant. Differences in host-plant size among treatments were partially responsible for these trends. When beetle densities were expressed as numbers per unit leaf area, treatment effects were lessened or lost. Changes in beetle density among treatments were accompanied by differences in fecundity among treatments, but not by differences in survival. Fecundity, calculated as numbers of eggs deposited per adult, was lower in high-diversity than in low-diversity plots. Survival rates (egg to late instar) and predation on eggs were not affected by plant species diversity.

Effects of tick population dynamics and host densities on the persistence of tick-borne infections

Journal Article Effects of Arena Size on Laboratory Evaluations of the Egg Parasitoids Trichogramma minutum, T. pretiosum, and T. exiguum (Hymenoptera: Trichogrammatidae) Get access Kevin W. Thorpe, Kevin W. Thorpe Search for other works by this author on: Oxford Academic PubMed Google Scholar Galen P. Dively Galen P. Dively Search for other works by this author on: Oxford Academic PubMed Google Scholar Environmental Entomology, Volume 14, Issue 6, 1 December 1985, Pages 762–767, https://doi.org/10.1093/ee/14.6.762 Published: 01 December 1985

1. Host density is hypothesized to be a major driver of variability in the responses and outcomes of wildlife populations following pathogen invasion. While the effects of host density on pathogen transmission have been extensively studied, these studies are dominated by theoretical analyses and small-scale experiments. This focus leads to an incomplete picture regarding how host density drives observed variability in disease outcomes in the field. 2. Here, we leveraged a dataset of hundreds of replicate amphibian populations that varied by orders of magnitude in host density. We used these data to test the effects of host density on three outcomes following the arrival of the amphibian-killing fungal pathogen Batrachochytrium dendrobatidis (Bd): the probability that Bd successfully invaded a host population and led to a pathogen outbreak, the magnitude of the host population-level decline following an outbreak and within-host infection dynamics that drive population-level outcomes in amphibian-pathogen systems. 3. Based on previous small-scale transmission experiments, we expected that populations with higher densities would be more likely to experience Bd outbreaks and would suffer larger proportional declines following outbreaks. To test these predictions, we developed and fitted a Hidden Markov Model that accounted for imperfectly observed disease outbreak states in the amphibian populations we surveyed. 4. Contrary to our predictions, we found minimal effects of host density on the probability of successful Bd invasion, the magnitude of population decline following Bd invasion and the dynamics of within-host infection intensity. Environmental conditions, such as summer temperature, winter severity and the presence of pathogen reservoirs, were more predictive of variability in disease outcomes. 5. Our results highlight the limitations of extrapolating findings from small-scale transmission experiments to observed disease trajectories in the field and provide strong evidence that variability in host density does not necessarily drive variability in host population responses following pathogen arrival. In an applied context, we show that feedbacks between host density and disease will not necessarily affect the success of reintroduction efforts in amphibian-Bd systems of conservation concern.

In some hosts of avian brood parasites, several populations apparently escape parasitism, while others are parasitized. Many migratory specialist brood parasites like common cuckoos, Cuculus canorus, experience a short breeding season, and in order to maintain local parasite populations host densities should be sufficiently high to allow efficient nest search. However, no studies have investigated the possible effect of host density on presence of cuckoo parasitism among populations of a single host species. Here, we investigated possible predictors of common cuckoo parasitism in 16 populations of reed warblers, Acrocephalus scirpaceus, across Europe. In more detail, we quantified the effect of host density, number of host breeding pairs, habitat type, mean distance to nearest cuckoo vantage point, predation rate and latitude on the presence of cuckoo parasitism while controlling for geographical distance among study populations. Host density was a powerful predictor of parasitism. We also found a less pronounced effect of habitat type on occurrence of parasitism, while the other variables did not explain why cuckoos utilize some reed warbler populations and not others. This is the first study focusing on patterns of common cuckoo-host interactions within a specific host species on a large geographic scale. The results indicate that if host density is below a specific threshold, cuckoo parasitism is absent regardless of the state of other potentially confounding variables.

Host density, host body size and ambient temperature have all been positively associated with increases in parasite infection. However, the relative importance of these factors in shaping long‐term parasite population dynamics in wild host populations is unknown due to the absence of long‐term studies. Here, we examine long‐term drivers of gill lice (Copepoda) infections in Arctic charr (Salmonidae) over 32 years. We predicted that host density and body size and water temperature would all positively affect parasite population size and population growth rate. Our results show that fish size was the main driver of gill lice infections in Arctic charr. In addition, Arctic charr became infected at smaller sizes and with more parasites in years of higher brown trout population size. Negative intraguild interactions between brown trout and Arctic charr appear to drive smaller Arctic charr to seek refuge in deeper areas of the lake, thus increasing infection risk. There was no effect of host density on the force of infection, and the relationship between Arctic charr density and parasite mean abundance was negative, possibly due to an encounter‐dilution effect. The population densities of host and parasite fluctuated independently of one another. Water temperature had negligible effects on the temporal dynamics of the gill lice population. Understanding long‐term drivers of parasite population dynamics is key for research and management. In fish farms, artificially high densities of hosts lead to vast increases in the transmission of parasitic copepods. However, in wild fish populations fluctuating at natural densities, the surface area available for copepodid attachment might be more important than the density of available hosts.

PDF HTML阅读 XML下载 导出引用 引用提醒 农业景观格局与麦蚜密度对其初寄生蜂与重寄生蜂种群及寄生率的影响 DOI: 10.5846/stxb201204190561 作者: 作者单位: 宁夏大学,宁夏大学 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金资助项目(30860164,31260429) Effects of host density on parasitoids and hyper-parasitoids of cereal aphids in different agricultural landscapes Author: Affiliation: Ningxia University、,Ningxia University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:农业景观格局与过程能够强烈影响寄生蜂对寄主的寻找及寄生作用,寄主密度亦是影响寄生蜂分布的重要因素,然而农业景观的格局和寄主密度对寄生蜂寄生率的相互影响是一项值得研究的工作。在简单与复杂2种麦田农业景观结构下,调查了麦蚜的分布格局与2种寄主密度下麦蚜的初寄生率与重寄生率,分析了景观结构对麦蚜密度的影响、景观格局与麦蚜密度对寄生蜂寄生率与重寄生率的影响及交互作用。结果表明:景观结构的复杂性对麦蚜分布和寄生蜂初寄生率与重寄生率的影响均不明显,但寄主密度与景观结构的复杂性对寄生蜂的影响存在着明显的交互作用,寄主密度与寄生率呈正相关,寄主密度较低时烟蚜茧蜂为优势种,寄主密度较高时燕麦蚜茧蜂为优势种。麦蚜初寄生蜂与重寄生蜂对寄主密度的反应与其形态学、体型大小以及生活史特征相关,初寄生蜂与重寄生蜂的群落组成显著影响其对麦蚜的寄生率,而与景观结构的复杂性关系不大。 Abstract:Several studies have shown positive responses of parasitism to either host density or landscape complexity. Many semi-natural arable habitats (Grasslands, woodlands, and wetlands) have been shaped by centuries of farming in China and worldwide. Established parasitoid populations have been recognized to provide pest management due to their high rates of consumption and precedence in wheat fields. However, no previous experiments have manipulated host density in agricultural landscapes of various complexity. Here we report the results of a field experiment conducted to determine how agricultural landscape complexity affects cereal aphids and how host density and agricultural landscape complexity jointly affect the parasitism, hyper-parasitism, and species diversity of parasitoids. Parasitism and hyper-parasitism were assessed by experimentally adding cereal aphids at low and high densities to commercial wheat fields located in two different agricultural landscapes in order to detect parasitism therein. Results showed that landscape complexity did not influence population density in cereal aphids. Landscape structure also did not influence parasitism and hyper-parasitism, contrary to our expectations. Increased host densities caused a trend of increasing abundance and species diversity in parasitoids and hyperparasitoids. Aphidius avenae Haliday parasitized a significantly greater proportion of hosts at low-host densities, while the opposite effect occurred for Aphidius gifuensis Ashmead. The discrepancy in responses of these parasitoids and hyper-parasitoids to host density is discussed in relation to differences in morphological traits, body size, and historical characteristics. The specific composition of parasitoid and hyper-parasitoid assemblage could significantly alter parasitism at various host densities at which landscape complexity and habitat composition impart negligible influence. Future studies should both evaluate plants with a more diverse range of traits and behaviors in landscapes with non-crop herbivore densities and span over more years to fully understand the impact of agricultural landscapes on species diversity and biological control service of parasitoids. 参考文献 相似文献 引证文献

The ecological factors that influence key life‐history traits such as brood size and sex ratio are enormously important to the survival and population dynamics of insect species.The effects of host density on life‐history characteristics of a parasitoid,Pteromalus apum, were examined in a field experiment conducted in the Åland Islands, Finland. This gregarious parasitoid preys on two co‐occurring butterfly species,Melitaea cinxiaandMelitaea athalia. The abundances of both butterfly species contribute to host density for the parasitoid.The goals of the study were to: (i) test sex allocation theory in a field setting by evaluating how host density and species affect parasitoid brood size and sex ratio; and (ii) understand how parasitoid foraging behaviour and co‐occurrence of multiple host species relate to life‐history traits of the parasitoid.Local host density and species were experimentally manipulated and natural parasitism was then allowed to occur. Larger brood sizes were found at low host density due to higher rates of superparasitism. Further, parasitoid brood size and sex ratio (proportion male progeny) were positively related, with a much stronger effect at low host density.These results illustrate that host density affects life‐history and population‐level traits of parasitoids. The fact that low host density was associated with high superparasitism (larger brood size) supports predictions based on the ‘apparent commensal’ indirect interaction between the host species. This work highlights the value of research that integrates interactions between species with the study of foraging behaviour and life‐history traits.

Effect of host density and location on the percentage parasitism, fertility and induced mortality of Aganaspis daci (Hymenoptera: Figitidae), a parasitoid of Ceratitis capitata (Diptera: Tephritidae)

High Host Density Promotes Ash Dieback

The effect of host density on parasitism byTrichogramma pretiosum Riley was studied by exposing groups of 150, 300, 600 or 1200 eggs of potato tuber moth to 2, 4 or 8 female parasites per group. The parasite exhibited a type 2 functional response. As host density increasedT. pretiosum parasitised more hosts, but at a decreasing rate. The attack coefficient (a′) decreased as parasite density increased, whereas the handling time (T h ) remained almost constant. The search rate (a) decreased with increasing host density.T. pretiosum responded to increasing host density by increasing the number of its encounters with hosts and the number of hosts it parasitised only up to host density of 300 when the parasite density was 2 and up to host density of 600 when the parasite densities were greater and then remained almost constant. The observed incidence of parasitism was higher than that expected on the assumption that the parasites behaved the same at higher host densities as at the lowest. When parasite density was raised from 2 to 8 females per group the percentage of female progeny fell from about 73 to about 48%. A 2-fold increase in the number of female progeny was observed when parasite density was reduced from 8 to 2 and also when the host density was raised from 150 to 1200 eggs.

In some hosts of avian brood parasites, several populations apparently escape parasitism, while others are parasitized. Many migratory specialist brood parasites like common cuckoos, Cuculus canorus , experience a short breeding season, and in order to maintain local parasite populations host densities should be sufficiently high to allow efficient nest search. However, no studies have investigated the possible effect of host density on presence of cuckoo parasitism among populations of a single host species. Here, we investigated possible predictors of common cuckoo parasitism in 16 populations of reed warblers, Acrocephalus scirpaceus , across Europe. In more detail, we quantified the effect of host density, number of host breeding pairs, habitat type, mean distance to nearest cuckoo vantage point, predation rate and latitude on the presence of cuckoo parasitism while controlling for geographical distance among study populations. Host density was a powerful predictor of parasitism. We also found a less pronounced effect of habitat type on occurrence of parasitism, while the other variables did not explain why cuckoos utilize some reed warbler populations and not others. This is the first study focusing on patterns of common cuckoo‐host interactions within a specific host species on a large geographic scale. The results indicate that if host density is below a specific threshold, cuckoo parasitism is absent regardless of the state of other potentially confounding variables.

Parasitoid reproduction is often limited by disposable time for accessing hosts or egg availability. In the case of synovigenic parasitoids (which mature eggs during their lifetime), theory predicts that egg limitation is infrequent because they are able to replenish their egg supply throughout life. However, this theory does not contemplate the effect of superparasitism on egg load. If superparasitism is applied as a strategy for modulating offspring sex ratio, as extra eggs are normally deposited in each host, it is to be expected that females experience egg limitation, especially when host density is high. In this article, the effect of host density on egg load, oviposition, and sex ratio in the tephritid parasitoid Diachasmimorpha longicaudata (Ashmead) was investigated. Specifically we analyzed the rate of oviposition per host and adjustments in offspring sex ratio in response to changes in host density and how these affect egg load. Parasitoids maintained a similar rate of oviposition, independent of host densities, except when host density fluctuated between 25 and 5 hosts per day. Females increased their oviposition rate and parasitism when confronted with 5 hosts, after having experienced a density of 25 hosts. Offspring sex ratio was biased in favor of females at high host density and with increasing prevalence of superparasitism. Results suggest that parasitoids have a strategy for maintaining high egg load in order to mitigate egg limitation, and for adjusting oviposition rate and offspring sex ratio with reference to previous oviposition experience.

Mass rearing of Habrobracon hebetor Say (Hymenoptera: Braconidae) on larvae of the Indian meal moth, Plodia interpunctella (Lepidoptera: Pyralidae): effects of host density, parasitoid density, and rearing containers

The foraging behavior of populations of Diadegma spp. (Hymenoptera: Ichneumonidae) attacking the diamondback moth, Plutella xylostella L. (Lepidoptera: Plutellidae), was studied in the field. The effect of host density on percentage parasitism was investigated at two spatial scales: that of the individual plant, as well as a “cluster of plants” at low, medium and high densities. Using binoculars, parasitoid searching was observed on host plants at different host densities over an 8-h period. Behavior was compared to that predicted under the Patch Selection Theory. Percentage parasitism was independent of host density at both spatial scales. However, the behavioral studies showed parasitoid aggregation behavior at higher host densities. The population displayed an imperfect preference for higher host densities in the first 4 h of foraging. In the second 4-h period, no preference was observed.