Many agroecosystems are unfavorable environments for natural enemies due to
high levels of disturbance. Habitat management, a form of conservation
biological control, is an ecologically based ...approach aimed at favoring natural
enemies and enhancing biological control in agricultural systems. The goal of
habitat management is to create a suitable ecological infrastructure within the
agricultural landscape to provide resources such as food for adult natural
enemies, alternative prey or hosts, and shelter from adverse conditions. These
resources must be integrated into the landscape in a way that is spatially and
temporally favorable to natural enemies and practical for producers to
implement. The rapidly expanding literature on habitat management is reviewed
with attention to practices for favoring predators and parasitoids,
implementation of habitat management, and the contributions of modeling and
ecological theory to this developing area of conservation biological control.
The potential to integrate the goals of habitat management for natural enemies
and nature conservation is discussed.
Sweetpotato has been the subject of little research worldwide compared with other major crop staples, and this is especially so for less developed countries where sweetpotato is critical for food ...security. This review synthesises information on plant protection issues that affect smallholder sweetpotato farmers in less developed countries to identify major issues and suggest research priorities. Though the pests and diseases of sweetpotato in less developed countries are largely common to industrialised systems, their relative importance differs and losses tend to be more severe as a result of differing agronomic practices and relative unavailability of management options and technical support that are important in developed countries. Smallholders are heavily reliant on cultural practices such as traditional forms of biological control using ants and livestock, fallowing and composting (sometimes with plant materials having biocidal properties). Crop protection methods that have been developed for use in sweetpotato production in developed countries, such as pathogenâtested planting material, early maturing varieties, pheromone trapping and pesticides are less accessible to, and relevant for, smallholders. Smallholders also typically harvest a given crop progressively which extends the period over which storage roots are potentially vulnerable to attack but reduces the risk of postâharvest losses. Human population growth in developing countries is leading to an increase in cropping intensity with shorter fallow periods and more years of continuous crops. This has the dual effect of depleting soil nutrients and increasing the potential for pest and pathogen buildâup. Associated with this, the adoption of strategies to manage crop nutrition, such as not burning crop residues, promote carryover of pests and pathogen inocula. As a consequence of these factors, sweetpotato yield losses from diseases, especially viruses, and pests, particularly weevils, can be high. Climate change is likely to result in more frequent drought and this will increase losses caused by sweetpotato weevils that are favoured by dry conditions. This review of sweetpotato pests and their management options concludes with suggestions for some future research priorities including the combination of traditional practices that have pest management outcomes with relevant practices from industrial production that are able to be transferred or modified for use in smallholder production. Increased technical support for decision making and diagnostics, including molecular approaches that have scope for field use, will be important in reducing the burden imposed by biotic threats to this important global crop.
The brown planthopper (BPH) Nilaparvata lugens, whitebacked planthopper (WBPH) Sogatella furcifera and smaller BPH Laodelphax striatellus increasingly exhibit resistance to insecticides and ...adaptation to resistant varieties, so they threaten food security. This review draws together, for the first time, information on the parasitoids of planthopper pests of rice from the non-English literature published in Asia. This is integrated with the English language literature to provide a comprehensive analysis. Planthopper pests of rice are attacked by a large range of parasitoids from Strepsiptera, Diptera and, especially, Hymenoptera. Levels of field parasitism vary widely between parasitoid species and locations. For many taxa, especially within Mymaridae, there is evidence that non-crop habitats are important as overwintering habitat in which alternative hosts are available. These source habitats may promote early season parasitism of pest Hemiptera in rice crops, and their movement into crops could be manipulated with applications of herbivore-induced plant volatiles. Non-crop plants can also provide nectar to improve parasitoid longevity and fecundity. Despite evidence for the importance of environmental factors affecting parasitoids of rice pests, the use of habitat manipulation to enhance biological control in the world's most important crop is surprisingly underrepresented in the literature. Current research in China, Vietnam and Thailand on ecological engineering, carefully selected vegetation diversity introduced without disrupting profitable farming, is briefly reported. Although the most important pest, BPH (N. lugens), is a migratory species, maintaining local communities of parasitoids and other natural enemies offers scope to prevent even r-selected pests from reaching damaging population densities.
1 The cultivated tomato, Lycopersicon esculentum, is an economically important worldwide crop. Current pest management techniques rely heavily on pesticides but trichome‐based host‐plant resistance ...may reduce pesticide use.
2 A review of the literature is provided on trichomes of wild Lycopersicon species and the effects of trichome‐based host‐plant resistance on arthropods. Solvents have been used to remove glandular trichome exudates and the resulting dimminution of their effects quantified. Correlational approaches to assess the relationship between the different trichome types and effects on pests have also been used.
3 Most studies have focused on Lepidoptera and Hemiptera, although some work has included Coleoptera, Diptera and Acarina, and both antibiotic and antixenotic effects have been demonstrated.
4 Natural enemies are a cornerstone of international pest management and this review discusses how the compatibility of this approach with trichome‐based host‐plant resistance is uncertain because of the reported negative effects of trichomes on one dipteran, one hemipteran and several Hymenoptera.
5 For trichome‐based host‐plant resistance to be utilized as a pest management tool, trichomes of wild species need to be introgressed into the cultivated tomato. Hybrids between the cultivated tomato and the wild species Lycopersicon hirsutum f. glabratum, Lycopersicon pennellii and Lycopersicon cheesmanii f. minor have been produced and useful levels of resistance to Acarina, Diptera and Hemiptera pests have been exhibited, although these effects may be tempered by effects on natural enemies.
6 This review proposes that studies on genetic links between fruit quality and resistance, field studies to determine the compatibility of natural enemies and trichome‐based host‐plant resistance, and a strong focus on L. cheesmanii f. minor, are all priorities for further research that will help realize the potential of this natural defence mechanism in pest management.
This paper reviews two aspects of agricultural biodiversity. 1. The
ways in which agricultural biodiversity may be increased to favour pest management are examined. At the simplest level, the ...structure within a monoculture may be altered by changing management practices to benefit natural enemies. At the other extreme, annual and perennial non-crop vegetation may be integrated with cropping, and biodiversity increased at the landscape level. 2. The existence of a hierarchy for the
types of benefits of increased biodiversity is discussed. Vegetational diversity can lead to suppression of pests via ‘top-down’ enhancement of natural enemy populations and by resource concentration and other ‘bottom-up’ effects acting directly on pests. Whilst such low-input pest management mechanisms are attractive in their own right, other (non-pest management related) benefits may simultaneously apply. These range from short-term benefits in crop yield or quality, longer term benefits for sustainability of the farming system and, ultimately, broad societal benefits including aesthetics, recreation and the conservation of flora and fauna. Examples are given of such multi-function agricultural biodiversity.
Diese Arbeit betrachtet zwei Aspekte landwirtschaftlicher Biodiversität. 1. Die Möglichkeiten, landwirtschaftliche Biodiversität zur Unterstützung eines Schädlingsmanagements zu erhöhen, werden untersucht. Im einfachsten Fall kann die Struktur innerhalb einer Monokultur durch veränderte Managementpraktiken geändert werden, so dass natürliche Gegenspieler davon profitieren. Im anderen Extrem können einjährige und mehrjährige Nichtnutzpflanzen in die Kultur integriert werden und die Biodiversität steigt auf Landschaftsebene an. 2. Das Vorhandensein einer Hierarchie der verschiedenen Typen von Vorteilen einer erhöhten Biodiversität wird diskutiert. Pflanzliche Diversität kann durch top-down Förderung von Populationen natürlicher Gegenspieler, durch Ressourcenkonzentration und durch andere bottom-up Effekte, die direkt auf Schädlinge einwirken, zu einer Unterdrückung von Schädlingen führen. Während solche low-input Mechanismen des Schädlingsmanagements durch sich selbst attraktiv sind, ergeben sich gleichzeitig auch andere Vorteile, die nicht mit dem Schädlingsmanagement zusammenhängen. Diese reichen von kurzfristigen Vorteilen bei Ertrag oder Qualität der Nutzpflanzen über mittelfristige Vorteile bei der Nachhaltigkeit des Bewirtschaftungssystems bis hin zu breiten, gesellschaftlichen Vorteilen, welche ästhetische Aspekte, Erholung und Schutz von Flora und Fauna einbeziehen. Beispiele für solche multifunktionelle landwirtschaftliche Biodiversität werden vorgestellt.
Herbivore plant damage induces emissions of semiochemicals termed herbivore‐induced plant volatiles (HIPVs). These volatile cues can attract the natural enemies of the attacking herbivores and ...protect the plant from further damage. Synthetic HIPV application to various crops has also been shown to attract natural enemies. In the present study, nectar plant rewards were combined with HIPVs in an ‘attract and reward’ approach. This combination might attract natural enemies into treated crops and provide them with food and shelter to maximise their survival and residency leading to increased parasitism and lower pest abundance. Trap catches of predators and scelionid parasitoids in treated grapevines were increased by methyl salicylate (MeSA) and methyl anthranilate (MeA) for 1 day and up to 5 days, respectively. The number of herbivorous thrips was also increased for up to 3 days post‐treatment. Buckwheat (Fagopyrum esculentum) reward increased catches of eulophid parasitoids and thrips over the 28‐day experiment. These results suggest that ‘attract’ and ‘reward’ can separately enhance local abundance of natural enemies but further work is required to fully realise the potential for synergistic effects.
1. In order to realize the full potential of natural enemies in integrated pest management, it is necessary to understand their population dynamics, particularly in relation to the role of refuges. ...Harvested and unharvested plots were established in a commercial hay lucerne Medicago sativa crop and the potential for the unharvested vegetation to constitute a refuge for natural enemies of Helicoverpa spp., one of the key pests, was evaluated. 2. The temporal and spatial dynamics of arthropod populations were evaluated using sequential samples from directional traps (pitfall and Malaise) and vacuum sampling in both crop treatments. 3. The spatial dynamics of predation were measured using 'sentinel' cards baited with Helicoverpa spp. eggs. 4. There was no significant directional movement of arthropods captured in pitfall traps, except for a 3-day period immediately after harvest when there was a net movement of the natural enemies Dicranolaius bellulus, Carabidae adults, spiders and the phytophagous mite Halotydeus destructor from harvested to unharvested plots. 5. There was net movement of adult Netelia producta, D. bellulus, Coccinella transversalis and Syrphidae as well as the pest Helicoverpa spp. from harvested to unharvested plots for 24 h following a harvest. 6. Densities of D. bellulus and C. transversalis within unharvested plots decreased with increasing distance from the borders with harvested plots. 7. Predation rates of Helicoverpa eggs placed in unharvested plots were broadly consistent with predator densities and decreased with distance from the harvested plots. 8. Predation rates of Helicoverpa eggs placed in harvested plots declined with increasing distance from unharvested plots, suggesting that natural enemies from the latter dispersed into regrowing lucerne. 9. Strips narrower than the plot width used (30 m) may be adequate to accommodate natural enemies displaced by harvesting. Unharvested refuge strips should ideally be spaced less than 30 m apart so that the natural enemies can contribute to biological control of pests over the entire width of harvested strips.
Finschhafen disorder (FD) affects coconut and oil palms in Papua New Guinea (PNG). It is characterised by yellow-bronzing of fronds which begins at the tips and progresses towards the petiole. ...Although the planthopper Zophiuma lobulata (Hemiptera: Lophopidae) has been posited as a cause of FD, the basis of the relationship has not been established. Studies conducted previously on FD predate the availability of DNA-based techniques to test for the involvement of plant pathogens such as phytoplasmas that cause yellows-type diseases in many plant taxa and are transmitted by the order of insects to which Z. lobulata belongs. In this study, polymerase chain reaction (PCR) assays found no evidence of phytoplasmas or bacteria-like organisms (BLOs) in tissues of coconut and oil palm symptomatic for FD and from Z. lobulata feeding on these plants. Further studies involved releasing Z. lobulata adults and nymphs onto caged, potted coconut and oil palms and onto palm fronds enclosed in mesh sleeves. In both experiments, chlorotic symptoms on the palms were observed in the presence of Z. lobulata. Insect-free control palms did not exhibit chlorotic symptoms of FD. In the frond sleeve experiment, only the fronds where Z. lobulata fed developed chlorosis indicating that the disorder is not systemic. Unlike most yellows-type diseases associated with Hemiptera, this study indicates that FD is because of a direct feeding effect on palms by Z. lobulata rather than transmission of a pathogen.
Many insects have coevolved with certain angiosperm taxa to act as pollinators. However, the nectar and pollen from such flowers is also widely fed upon by other insects, including entomophagous ...species. Conservation biological control seeks to maximise the impact of these natural enemies on crop pests by enhancing availability of nectar and pollen‐rich plants in agroecosystems. A risk with this approach is that pests may also benefit from the food resource. We show that the flowers of some plants (viz., buckwheat, Fagopyron esculentum Moench and dill, Anethum graveolens L.), and the extrafloral nectaries of faba bean (Vicia faba L.) benefit both Copidosoma koehleri Blanchard (Hymenoptera: Encyrtidae) and its host, the potato pest, Phthorimaea operculella Zeller (Lepidoptera: Gelechiidae). In contrast, phacelia (Phacelia tanacetifolia Benth) and nasturtium (Tropaeoleum majus L.) benefited only the parasitoid. When adult moths of P. operculella were caged with flowers of phacelia or nasturtium, longevity of males and females, egg laying life, fecundity, average oviposition rate, and number of eggs in ovaries at death were no greater than in the control treatment with access to shoots without flowers plus water. All the foregoing measures were increased compared to the control when the moths were allowed access to dill, buckwheat or faba bean extrafloral nectaries. Such ‘selectivity’ has the potential to make the use of floral resources in conservation biological control more strategic. We present morphometric and observational evidence to illustrate how such mechanisms may operate.
Trichome‐based host plant resistance of Lycopersicon (Solanaceae) species offers the potential to reduce pesticide use in tomato production, but its compatibility with biocontrol agents is largely ...unknown. The effect of trichome‐based host plant resistance on the lacewing biocontrol agent, Mallada signata, was assessed for five accessions of L. cheesmanii, four accessions of Lycopersicon hirsutum, two accessions of Lycopersicon pennellii, and one Lycopersicon esculentum cultivar. An intact leaf was isolated from the whole plant using Tangletrap to coat the petiole and 20 green peach aphids Myzus persicae (Sulzer) (Homoptera: Aphididae) were placed on the leaf surface. After 24 h, 10 lacewings were placed on the leaf. The numbers of dead, trapped by exudates, untrapped and predated lacewings and aphids, and the numbers that had left the leaf were recorded a further 24 h later. Differences in insect designations between accessions were analysed using ANOVA. A General Linear Model (GLM), consisting of the densities of each trichome type and leaf area, was fitted to the data to determine the role of trichomes on the observed effects on lacewings and aphids. Lacewing mortality was greater on one accession of L. pennellii and one accession of L. hirsutum than on L. esculentum. The GLM indicated that type IV trichomes decreased the numbers of aphids predated, and increased cannibalism and, along with type III trichomes, increased entrapment‐related predator mortality. Although there were no differences in the numbers of predated aphids, with the majority predated for all accessions, the compatibility of trichome‐based host plant resistance of Lycopersicon species and the biocontrol of aphids by lacewings is questionable.
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