Local predator composition and landscape affects biological control of aphids in alfalfa fields

The biological control service supplied to croplands is a result of the predator community present within a focal crop, which is likely influenced by surrounding landscape composition and configuration. In this study, using cage experiments in two regions near Santiago, we determined if predator communities supplied a significant biological control service in alfalfa fields, examined how the abundance of exotic and native coccinellids, as well as other key predator groups, influenced biological control of aphids and measured how landscape composition and heterogeneity at three spatial scales influenced this service. We found that predators significantly suppressed aphid populations in both regions, but the relative importance of predators versus landscape variables on biological control differed between regions. In the region where predators were abundant, biological control was higher and related to the abundance of native coccinellids and syrphids, highlighting the importance of native species as providers of crucial ecological services. In the region where predators were not abundant, biological control was lower, and it was related to landscape composition, being positively associated with the abundance of woodlots and urban habitats, and negatively associated with fruit crops in the landscape. Therefore, landscape effects on biological control service may be weaker than local factors, and only become important when local predator abundance is low.     

Mitigating the effects of insecticides on arthropod biological control at field and landscape scales

Integrated pest management (IPM) programs emphasize the combination of tactics, such as chemical and biological control, to maintain pest populations below economic thresholds. Although combining tactics may provide better long-term sustainable pest suppression than one tactic alone, in many cases, insecticides and natural enemies are incompatible. Insecticides can disrupt natural enemies through lethal and sub-lethal means causing pest resurgence or secondary pest outbreaks. Legislative actions such as the Food Quality Protection Act (US) and the Directive on Sustainable Use of Pesticides (EU) have placed greater restrictions on insecticides used in agriculture, potentially enhancing biological control. Here we focus on the effects of insecticides on biological control, and potential mitigation measures that can operate at different scales. At the farm scale, natural enemies can be conserved through the use of selective insecticides, low doses, special formulations, creation of refugia, special application methods, and targeted applications (temporal or spatial). At the landscape scale, habitat quality and composition affect the magnitude of biological control services, and the degree of mitigation against the effects of pesticides on natural enemies. Current research is teasing apart the relative importance of local and landscape effects of pesticides on natural enemies and the ecosystem services they provide, and the further development of this area will ultimately inform the decisions of policy makers and land managers in terms of how to mitigate pesticide effects through habitat manipulation.     

Natural flightless morphs of the ladybird beetle Adalia bipunctata improve biological control of aphids on single plants

The challenge of using ladybird beetles for biological control of insect pests such as aphids is that the adult beetles tend to fly away from the host plants. Therefore, flightless ladybirds might improve biocontrol. There are several artificial ways to obtain flightless beetles, but it may be preferable to use natural variation in flight ability. We investigated, for the first time, biocontrol by inundative augmentation of natural flightless morphs of the ladybird beetle Adalia bipunctata. Microcosm experiments using single leaves with one of three species of aphid revealed no differences in consumption behavior between flightless and winged beetles. Monitoring for 48 h of single, caged pepper plants infested with aphids of Myzus persicae nicotianae or Aulacorthum solani showed that flightless beetles had a longer residence time on the plants than winged beetles. This only translated into significantly better biocontrol of M. persicae. Despite their difference in residence time, both beetle morphs reduced the population growth of A. solani. This is probably explained by the tendency of A. solani to drop from the plant upon disturbance, and we predict that flightless beetles may outperform winged ones in the long term. Overall, our results provide a proof of principle that natural flightless A. bipunctata can improve biocontrol of aphids by ladybird beetles. However, we recognize that the effect of biocontrol will vary with the species of aphid used and that further examination in long term and large scale experiments is required.     

北京东北旺农田景观步甲群落结构的时空动态比较

2000年5～10月在北京海淀区东北旺实验基地,采用陷阱法对林地、农田边界和农田3类生境共14个处理的步甲进行了取样。并在此基础上分析了不同生境和不同季节步甲科昆虫群落的动态分布特征。结果表明,林地和农田边界类生境相对于农田类生境拥有更多的步甲个体数和物种数;无论是优势种还是稀有种都趋向于在林地和边界处生活;边界对相邻农田步甲群落的多样性有积极影响;对边界进行适度的干扰(秋季翻耕)有利于提高步甲群落的个体数量;农田生境中灌溉、施肥和秸秆还田对农田中步甲群落的个体数量和物种数量的空间分布均无显著影响。此外,还结合步甲的时空分布特性对步甲受威胁状况进行了初步的分析。     

Age-dependent functional response of Aphidius matricariae (Hymenoptera: Braconidae) on tobacco aphid,Myzus persicae nicotianae (Hemiptera: Aphididae)

This study was performed to investigate the age-dependent functional response of Aphidius matricariae Haliday (Hymenoptera: Braconidae) at varying densities of tobacco aphid, Myzus persicae nicotianae Blackman (Hemiptera: Aphididae). Six densities (2, 4, 8, 16, 32, and 64 numbers) of third instar nymphs of M. persicae nicotianae were daily exposed to one pair of 1-day-old A. matricariae until the parasitoid female died. Each host aphid density was replicated 10 times. The experiments were conducted at constant environmental conditions (25 ± 1 °C, 70 ± 5% RH and 16:8h L:D photoperiod). The logistic regression model demonstrated that the functional response of A. matricariae was type III in the second day and type II in the first day and from third to the end of adult parasitoid lifetime. The handling time (T_h) was lowest in the first day (0.2305 h) and highest in the sixth day (2.9296 h) of the parasitoid’s life. The searching efficiency (a) values were 0.0573, 0.0649, 0.0503, 0.0229, and 0.0077 h^?1 in the first, third, fourth, fifth, and sixth days of the parasitoid’s life, respectively. Also, the b value for type III functional response was 0.0147 in the second day. The values of maximum attack rate (T/T_h) ranged from 104.12 nymphs/24 h in the first day to 19.8 nymphs/24 h in the sixth day of parasitoid’s life. Based on the results, A. matricariae showed a high potential to control the population of tobacco aphid and the highest efficiency gained in the first half of the female parasitoid life.     

Looking deeply into the nature of biological control

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Why two species of parasitoids showed promise in the laboratory but failed to control the soybean aphid under field conditions

Following the rapid spread of soybean aphid, Aphis glycines in North America in the early 2000’s, biological control was identified as a cost-effective approach for management of this invasive pest. Two parasitoid species, Binodoxys communis and Aphidius colemani, were considered as potential candidates for classical and inundative biological control, respectively. The objectives of the present study were to determine the overwintering capacity of B. communis under climatic conditions prevailing in northeastern North America, and to measure parasitism and dispersal capacity of A. colemani when released in soybean fields. Field and laboratory assessments showed that the Chinese strain of B. communis, Harbin 2002, has a very poor capacity to enter into diapause (<0.8%), and thus to establish in North America. We suggest that this strain has gradually lost its ability to enter diapause during the extended periods of quarantine and laboratory confinement, during which it was continuously exposed to non-diapause rearing conditions. A. colemani did not show strong potential to control A. glycines. Following the release of approximately 8400 females in experimental plots, only 113 mummies were recovered within a radius of 60 m from the release point. Although both parasitoids were promising in controlled environments, the B. communis Harbin 2002 strain and the A. colemani commercial strain did not show strong potential to control A. glycines populations in soybean fields.     

陕北黄土高原景观破碎化的时空动态研究

景观破碎化受到自然环境背景及社会经济活动的影响,并限制区域发展.为揭示景观破碎化的时空变化特征,整合了MODIS(中分辨率成像光谱仪)影像逐旬数据与多时段景观类型数据,并对其进行了分析.比较1987～2002年景观破碎化的年际差异表明,陕北黄土高原的景观破碎化过程较缓慢,但具有区域差异,且与景观类型组成息息相关.结果表明,林地的破碎化水平变化显著,而农、草地的破碎化水平变化相对缓慢.年际变化分析有助于说明区域景观破碎化的趋势,而年内季节变化则能帮助认识景观破碎化过程的周期规律.     

Potential for biotic interference of a classical biological control agent of the soybean aphid

The degree to which resident biota can inhibit the ability of an introduced biological control agent to establish and be effective is termed biotic interference. Studying biotic interference prior to a release using the actual agent is logistically difficult, however, due to quarantine restrictions. An alternative solution is to study biotic interference against a surrogate species in the intended range of introduction, with the expectation that biotic interference against the actual agent will be similar. This study assessed how biotic interference, mostly by generalist predators, may affect establishment of classical biological control agents of the soybean aphid, Aphis glycines Matsumura, in North America. The parasitoid Aphidius colemani Viereck was used as a surrogate for Asian aphidiine braconids such as Binodoxys communis (Gahan). We conducted a factorial field experiment that measured the effect of releasing A. colemani and of excluding resident natural enemies using field cages on soybean aphid populations. We also conducted molecular gut-contents analyses on predators collected in release plots to determine which species fed upon A. colemani. Releasing A. colemani in open field plots increased soybean aphid control beyond that observed in open field plots alone, despite indications that intraguild predation of A. colemani occurred. Thus, biotic interference was not sufficient to eliminate the contribution of A. colemani on soybean aphid suppression during the course of our experiment. Molecular gut-contents analysis revealed that at least two predators, Harmonia axyridis (Pallas) and Chrysoperla carnea Stephens, engaged in intraguild predation against A. colemani. The prolonged effect of intraguild predation on parasitoid establishment remains to be determined.     

Stable oscillations in mathematical models of biological control systems

Summary Oscillations in a class of piecewise linear (PL) equations which have been proposed to model biological control systems are considered. The flows in phase space determined by the PL equations can be classified by a directed graph, called a state transition diagram, on anN-cube. Each vertex of theN-cube corresponds to an orthant in phase space and each edge corresponds to an open boundary between neighboring orthants. If the state transition diagram contains a certain configuration called a cyclic attractor, then we prove that for the associated PL equation, all trajectories in the regions of phase space corresponding to the cyclic attractor either (i) approach a unique stable limit cycle attractor, or (ii) approach the origin, in the limitt→∞. An algebraic criterion is given to distinguish the two cases. Equations which can be used to model feedback inhibition are introduced to illustrate the techniques.     

新一代生物防治及其在天敌瓢虫中的研究进展

生物防治是一种利用自然天敌控制有害生物的手段.当前生物防治的发展面临着使用成本高和效果不稳定的两大难题.这要求我们更精准地选育和释放天敌.随着测序技术的进步,学界提出了新一代生物防治(Next Generation Biological Control),旨在利用遗传学和基因组学来认识天敌昆虫种下水平的多样性和变异规律...     

生防细菌产生的拮抗物质及其在生物防治中的作用

利用生防细菌防治植物病害是生物防治的一个主要内容．生防细菌防治植物病害发生发展的一个重要机制是产生拮抗物质．生防细菌的拮抗物质种类多,作用范围广谱．同一种拮抗物质可以由多种细菌菌株产生,而同一细菌也可以产生多种不同结构的拮抗物质．运用现代分子生物学技术和先进的分析测试手段可以加快对产生拮抗物质生防细菌的研究,了解生防细菌在寄主植物根围和叶围的定植效果。明确拮抗物质在生物防治中的作用．拮抗物质的产生除与细菌基因型有关外,一些外在的生物和非生物因素如病原菌存在与否、温度、pH和C、N营养等也影响拮抗物质产生．文中论述了生防细菌应用中存在的问题。指出混合菌剂的研制对防止病原菌抗性产生具有重要作用,应是今后生防菌剂研制中的重点．     

The impact of insecticide resistance in the currant-lettuce aphid, Nasonovia ribisnigri, on pest management in lettuce

Abstract 1 This paper reports on experiments to determine how two different insecticide resistance phenotypes in the aphid Nasonovia ribisnigri (Mosley), which is a major pest of lettuce, change its susceptibility to pyrethroid insecticides and the carbamate pirimicarb. 2 A novel statistical approach determined how the effectiveness of different insecticides was changed by the two resistance phenotypes. This compared the between‐plant distribution of aphid numbers, as opposed to the mean number of aphids per plant. 3 Results from field cage experiments showed that the effect of the resistances differed. Pyrethroid resistance resulted in lower mortality immediately after application of pyrethroids, whereas resistance to pirimicarb shortened the time over which the chemical was effective. 4 The results of laboratory bioassays suggested that these two resistances were not found together in N. ribisnigri. However, the results reported here contradict this assertion. 5 Experiments with insecticide residues showed that reproduction of resistant N. ribisnigri was greater than that of susceptible N. ribisnigri on plants with ageing insecticide residues, even in circumstances where mortality of resistant and susceptible clones of N. ribisnigri were similar. 6 If more than a few aphids are found on a plant then a whole consignment can be rejected for processing. The results reported here suggest that the effect of both insecticide resistances in N. ribsinigri will be to increase the proportion of lettuce heads with an unacceptable number of aphids on them, leading to increased rejection of plants for processing.     

Role of mermithid nematodes in biological control of mosquitoes

Mermithid nematodes have been reported from at least 63 species of mosquitoes from all over the world, but until recently they have received little attention. Such nematodes are prime candidates as biological control agents because they have adapted to the life cycle of the host; are host specific; produce high levels of parasitism; kill the hosts; are easily handled; have a high reproductive potential; are free swimming and can be disseminated easily in the infective stage; and can be used in an inundative or inoculative manner to control mosquitoes. Nevertheless, with the exception of one mermithid species, little is known about factors that influence parasitism in mosquitoes. Also, only one species of mermithid has been successfully mass cultured to date. The exception is the mermithid Reesimermis nielseni. With this mermithid, high levels of parasitism can be obtained in natural populations of mosquitoes at reasonable dosages; preparasitic nematodes can be applied easily by using many of the standard techniques used to apply insecticides; and R. nielseni can establish itself in many of the sites in which it is released. The same potentials exist for mermithids of other aquatic insects.     

Effects of landscape connectivity on the spatial distribution of insect diversity in agricultural mosaic landscapes

European agricultural landscapes are mosaics of intensively cultivated areas and semi-natural elements. Although comprising only a small fraction of the total area, semi-natural elements provide habitat for most of the landscape biodiversity. Agricultural intensification has increasingly fragmented semi-natural elements and species numbers are in decline. Insights into the effects of landscape structure on species’ distributions within and among semi-natural habitats are needed to conserve biodiversity in agricultural landscapes more effectively. We investigated the landscape- and habitat-specific diversity partitions of wild bees, true bugs, and carabid beetles in two differently structured agricultural landscapes in Switzerland. In each landscape, we partitioned the total species diversity (γ) into its additive components within (_P) and among patches (β_P) and among habitats (β_H). In the landscape characterized by a patchy, isolated distribution of habitat elements, among-patch diversity (β_P) explained 44% of the total species richness (γ) and was significantly higher than expected under a random distribution of samples among habitat patches; in the landscape with higher habitat connectivity, among-patch diversity (β_P) comprised 32% of the total species richness (γ) and did not differ from the random expectation. Habitat-specific within-patch contributions to species richness were similarly low across habitat types (_P=23–24%) in the patchy landscape, whereas in the more connected landscape within-patch partitions tended to be higher and differed among habitat types (_P=22–38%). Functionally different groups of bees, true bugs, and carabids also responded differently to landscape structure in a manner that was consistent with known differences in resource specialization and dispersal ability. Differences in diversity partitions among landscapes and taxa indicate the need for flexible conservation strategies. Conservation of habitat-specific diversity may require more habitat patches in landscapes that have lower habitat connectivity and low within-patch diversity (_P) than in landscapes with higher within-patch diversity (_P).     

Screening Trichoderma species for biological control activity against Phytophthora ramorum in soil

Despite efforts of eradication and sanitation, Phytophthora ramorum persists in the United States and abroad. Fungicides have limited effectiveness, but there are concerns that they may only inhibit pathogen growth and hasten resistance development after repeated fungicide applications. Biological control is an active control measure that can work continuously as long as the agent is alive and active. The goal of this study was to examine whether Trichoderma spp. have the potential as a biological control agent against P. ramorum. Sixteen Trichoderma spp. isolates were screened for mycoparasitism of P. ramorum in a dual culture assay. The different Trichoderma spp. isolates demonstrated variable mycoparasitic activities with some isolates showing no activity while others completely eliminated the pathogen after 4 weeks. Seven isolates of T. asperellum were consistent among replicated trials in eliminating recovery of P. ramorum from the exposed agar plugs and preventing leaf disk necrosis. Further testing of six T. asperellum isolates against two different P. ramorum isolates (A1 and A2 mating types) resulted in the same high level of mycoparasitic activity. Soil assays involving P. ramorum-infested potting mix and selected Trichoderma spp. isolates demonstrated that two isolates (04-22 and 02-64) were consistent among the repetitions to eliminate P. ramorum propagules to non-detectable levels. Based on these results, specific T. asperellum isolates have the potential to remediate P. ramorum-infested soil and have the potential to be developed into a commercially-viable product.     

Estimating economic benefits of biological control of Ambrosia artemisiifolia by Ophraella communa in southeastern France

The North American common ragweed, Ambrosia artemisiifolia, which produces highly allergenic pollen, is invasive in different parts of the world, including Europe. In 2013, common ragweed in northern Italy was found attacked by another accidentally introduced species, the North American leaf beetle Ophraella communa, which is used for biological control of common ragweed in China. Since the establishment of O. communa, ragweed pollen concentrations in northern Italy have significantly dropped. Here we set out to estimate the potential economic benefits of establishment of O. communa in the Rhône-Alpes region in south-eastern France, where detailed data on the economic impact of common ragweed are available. Extrapolating from the change in airborne ragweed pollen concentrations in the Milan area, we estimated that establishment of O. communa in the Rhône-Alpes region will reduce the number of days with ragweed pollen concentrations at which sensitive people express symptoms by 50% and the medical costs due to common ragweed by 5.2–6.8 M € annually. Our findings suggest that investments of public funds are justified to conduct a complete assessment of the potential risks and benefits associated with the accidental establishment of O. communa in Europe.     

Application of Bacillus subtilis in the biological control of the phytopathogenic fungus Sporisorium reilianum

Sporisorium reilianum is the causal agent of head smut in corn, a worldwide disease that causes significant economic losses in the principal areas where maize is cultivated. To attack this problem, resistant commercial hybrids and synthetic fungicide seed treatment have been used, but with low effectiveness. In this study, a native strain of Bacillus subtilis isolated from the soil of corn crops in Mixquiahuala, Hidalgo, in central Mexico, was applied as a seed treatment in the field to test for the biological control of head smut. It significantly decreased the Smut Incidence Percentage (SIP) while increasing maize productivity. This work represents the first report in which B. subtilis has been used to control S. reilianum in the field.     

Environmental safety of biological control: Policy and practice in New Zealand

Introduction of biological control agents into New Zealand is regulated under the Hazardous Substances and New Organisms Act 1996 (HSNO). The legislation is strongly focused on the health and safety of people and the environment. HSNO is implemented by the Environmental Risk Management Authority, a quasi-judicial body of 6–8 people appointed by the Minister for the Environment. The process by which biological control applications are received and processed is described. Two case studies of weed biological control agents which have been through the HSNO process, and the scientific issues that arose in considering the environmental safety of these agents are discussed. The case studies presented are the applications to release the gall fly Procecidochares alani (Diptera: Tephritidae) to control mist flower Ageratina riparia, and three biological control agents, Macrolabis pilosellae (Diptera: Cecidomyiidae), Cheilosia urbana, and Cheilosia psilophthalma (Diptera: Syrphidae) for biological control of hawkweeds (Hieracium spp.). Both applications were approved for agent release into the environment.