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1.
The influence of three margin strip treatments (wildflower strips, grass strips and spontaneous vegetation) adjacent to apple orchards on the biological control of Dysaphis plantaginea Passerini (Hemiptera: Aphididae) was compared during two consecutive years. The wildflower strips provided the highest amount of floral resources. Within the margin strips, hoverflies responded positively to higher resource provisioning whereas ladybird abundance did not differ between strip treatments. Within the orchards, the presence of parasitoids, hoverflies, and ladybirds in aphid colonies and the predation of sentinel aphids were not significantly affected by the adjacent strip treatments. The number of natural enemies observed in aphid colonies was mainly driven by aphid number. Aphid numbers were higher close to the margin strips suggesting that aphid colonization from orchard edges may counteract the positive effect of wildflower strips on natural enemy abundance and on a reduction of aphid infestation. The results confirm the positive influence of floral resource provisioning by wildflower strips on the conservation of aphid natural enemies, but also suggest that effects of wildflower strips on aphid regulation inside orchards are not very strong compared with spontaneous vegetation naturally occurring in the margins.  相似文献   

2.
Sowing of wildflower strips has been integrated in agri-environment schemes of several European countries. Their beneficial effects on natural enemies of pest insects are well documented but (1) the desired spill-over into crop fields has not always been demonstrated, and (2) the need to adapt sown mixtures to regional climatic differences has been rarely addressed.We set up a multi-site experiment in different French climatic regions to compare effects of a wildflower strip with a grass mixture and spontaneous vegetation. The design included five regions, three to five fields per region and the three strip treatments being repeated in each field. We tested strip treatment effects on vegetation (plant species richness, plant and flower cover) and on natural enemies (hoverflies, ladybirds, aphid predation). In a subset, we further analysed the spill-over into winter wheat fields including natural enemies and pest insects (cereal aphids, leaf beetles).The wildflower strip mixture developed well in all regions and increased plant species richness and flower cover compared with grass strips and spontaneous vegetation. We found a corresponding higher hoverfly abundance and aphid predation in wildflower strips that were consistent in all regions, whereas ladybird abundance was not affected. A significantly higher hoverfly abundance, aphid predation and aphid parasitism in wheat fields close to wildflower strips indicated a spill-over. No corresponding margin treatment effects were observed for aphid and leaf beetle abundance in the field. A multivariate analysis comparing the influence of climate and vegetation parameters showed that floral cover better explained variation in natural enemy abundance and predation than climate. Our results demonstrated that similar mixtures of native plants can be used over large climatic gradients to improve biocontrol. Further research is needed to improve spill-over into crop fields and to obtain consistently strong effects in different climate zones.  相似文献   

3.
Non-crop vegetation of field margins provides resources for natural enemies of crop herbivores. However, it is still not well known whether this resource provisioning effect is strong enough to improve herbivore regulation within crop fields and which plant species and functional groups favour this ecosystem service. A better understanding of the interactions between field margin vegetation and herbivore regulation is crucial to evaluate management strategies and to design suppressive plant mixtures. We surveyed 64 wheat and oilseed rape fields of Western France for two years (16 fields per year and crop) in order (1) to identify plant diversity or group effects on herbivore regulation within crop fields and (2) to identify species within plant groups that improve regulation. Herbivores, herbivore damage and natural enemies were monitored on crop plants at a distance of 5 and 50 m from the field margin. At the same time, the cover and phenological stage of all vascular plants were estimated in the adjacent field margin. The study demonstrated a positive relationship between the cover of entomophilous plant species that were flowering at the survey date and response variables related to herbivore regulation. Plant species richness and the cover of plant species taxonomically close to crop plants had a small influence on herbivores and natural enemies in wheat whereas related wild Brassicaceae increased herbivory and decreased herbivore regulation in oilseed rape. Within the entomophilous flowering plants, several species were significantly related to a better herbivore regulation in univariate analyses. Multivariate ordination techniques allowed the identification of plant species influencing several response variables of herbivore regulation at the same time. Our study demonstrated the importance of entomophilous species that flowered at peak infestation of crop herbivores. Spontaneous field margins rich in flowering entomophilous species provide an important ecosystem service without expensive sowing of seed mixtures.  相似文献   

4.
Symbiotic bacteria in herbivorous insects can have strong beneficial impacts on their host's survival, including conferring resistance to natural enemies such as parasitoid wasps or pathogens, while also imposing energetic costs on the host, resulting in cost‐benefit trade‐offs. Whether these trade‐offs favour the hosting of symbionts depends on the growth environment of the herbivore. Long‐term experimental grassland studies have shown that increasing plant species richness leads to an increased diversity of associated herbivores and their natural enemies. Such a change in natural enemy diversity, related to changes in plant diversity, could also drive changes in the community of symbionts hosted by the herbivorous insects. Aphids are one model system for studying symbionts in insects, and effects of host‐plant species and diversity on aphid‐symbiont interactions have been documented. Yet, we still understand little of the mechanisms underlying such effects. We review the current state of knowledge of how biodiversity can impact aphid‐symbiont communities and the underlying drivers. Then, we discuss this in the framework of sustainable agriculture, where increased plant biodiversity, in the form of wildflower strips, is used to recruit natural enemies to crop fields for their pest control services. Although aphid symbionts have the potential to reduce biological control effectiveness through conferring protection for the host insect, we discuss how increasing plant and natural enemy biodiversity can mitigate these effects and identify future research opportunities. Understanding how to promote beneficial interactions in ecological systems can help in the development of more sustainable agricultural management strategies.  相似文献   

5.
The population decline of the European hare (Lepus europaeus) in Switzerland is generally attributed to low leveret survival. A significant intensification of agricultural practices led to a landscape transformation that reduced leveret survival by increasing negative factors such as predation pressure. Habitat improvement by means of wildflower strips has yielded some positive effects on European hare population trends, probably by improving food supply and providing year-round cover from predation. For this study, remote cameras were used to examine relationships between landscape and wildflower strip variables and the frequency of predator visits to wildflower strips as well as the probability of them visiting core areas of the strips. Of a total of 1586 visits of potential predators to wildflower strips, 91% were mammals and 9% were birds. Predators were more frequently observed at the edges of the wildflower strips than in their cores (72% of visits by mammalian predators and 76% by avian predators were at the edge). The results revealed that the frequency of observing predators was negatively correlated with adjacent crop height and the distance of the wildflower strip from settlements, roads and forests or hedgerows. The probability of a predator penetrating the core of the wildflower strip was negatively correlated with the vegetation cover, especially with the cover of wood, herbaceous plant species and teasel (Dipsacus fullonum). Appropriate management of wildflower strips by considering their spatial placement, creating low margin to surface area ratios and promoting heterogeneous wildflower structure can thus lead to reduced predator pressure on leverets as well as on ground-nesting birds.  相似文献   

6.
7.
Within-crop habitat manipulations have the potential to increase the biological control of pests in horticultural field crops. Wildflower strips have been shown to increase the abundance of natural enemies, but there is little evidence to date of an impact on pest populations. The aim of this study was to determine whether within-crop wildflower strips can increase the natural regulation of pests in horticultural field crops. Aphid numbers in plots of lettuce grown adjacent to wildflower strips were compared with those in plots grown in the absence of wildflowers. The presence of wildflower strips led to a decrease in aphid numbers on adjacent lettuce plants during June and July, but had less impact in August and September. The decrease in aphid numbers was greatest close to the wildflower strips and, the decrease in aphid numbers declined with increasing distance from the wildflower strips, with little effect at a distance of ten metres. The main natural enemies found in the crop were those that dispersed aerially, which is consistent with data from previous studies on cereal crops. Analysis and interpretation of natural enemy numbers was difficult due to low recovery of natural enemies, and the numbers appeared to follow changes in aphid abundance rather than being directly linked to the presence of wildflower strips. Cutting the wildflower strips, to remove floral resources, had no impact on the reduction in aphid numbers achieved during June and July, but decreased the effect of the wildflower strips during August and September. The results suggest that wildflower strips can lead to increased natural regulation of pest aphids in outdoor lettuce crops, but more research is required to determine how this is mediated by natural enemies and how the impact of wildflower strips on natural pest regulation changes during the growing season.  相似文献   

8.
Wildflower strips are used to increase natural enemies of crop pests and to conserve insect diversity on farmland. Mollusks, especially slugs, can affect the vegetation development in these strips considerably. Although recent theoretical work suggests that more diverse plant communities will exhibit greater resistance against herbivore pressure, empirical studies are scarce. We conducted a semi‐natural experiment in wildflower strips, manipulating trophic structure (reduction in herbivorous mollusks and reduction in major predators) and plant diversity (2, 6, 12, 20 and 24 sown species). This design allowed us to assess the effect of plant diversity, biomass and composition on mollusks, and vice versa, the effect of mollusc abundance on vegetation. Seven species of mollusks were found in the strips, with the slugs Arion lusitanicus, Deroceras reticulatum and Deroceras panormitanum being most frequent. We found a negative relationship between plant diversity and mollusk abundance, which was due predominantly to a decrease in the agricultural pest species A. lusitanicus. These results are consistent with the hypothesis that plant diversity can reduce the impact of herbivores. However, plant identity also had an effect on mollusks, and accounted for a much larger fraction of the variation in mollusk communities than biodiversity effects. While overall plant diversity decreased during the 3 years of the study, in the final year the highest plant diversity was found in the plots where mollusk populations were experimentally reduced. We conclude that selective feeding by generalist herbivores leads to changes in plant community composition and hence reduced plant diversity. Our results highlight the importance of plant biodiversity as protection against generalist herbivores, which if abundant can in the long term negatively impact plant diversity, driving the system along a “low plant diversity – high mollusk abundance” trajectory.  相似文献   

9.
Adaptation to novel host plants is a much‐studied process in arthropod herbivores, but not in their predators. This is surprising, considering the attention that has been given to the role of predators in host range expansion in herbivores; the enemy‐free space hypothesis suggests that plants may be included in the host range of herbivores because of lower predation and parasitism rates on the novel host plants. This effect can only be important if natural enemies do not follow their prey to the novel host plant, at least not immediately, thus allowing the herbivores to adapt to the novel host plant. Hence, depending on the speed with which natural enemies follow their prey to a new host plant, enemy‐free space on novel host plants may only exist for a limited period. This situation may presently be occurring in a system consisting of the herbivorous moth Thyrinteina arnobia Stoll (Lepidoptera: Geometridae) that attacks various species of Myrtaceae, such as guava (Psidium guajava L.) and jaboticaba (Myrciaria spp.), in Brazil. Since the introduction of eucalyptus (Myrtaceae) species into this country some 100 years ago, the moth has included this plant species in its host range and frequently causes outbreaks, a phenomenon that does not occur on the native host plant species. This suggests that the natural enemies that attack the herbivore on native species are not very effective on the novel host. We tested this hypothesis by studying the searching behaviour of one of the natural enemies, the omnivorous predatory bug Podisus nigrispinus (Dallas) (Heteroptera: Pentatomidae). When offered a choice between plants of the two species, the predators (originally collected in eucalyptus plantations) preferred guava to eucalyptus when both plant species were clean, infested with herbivores, or damaged by herbivores but with herbivores removed prior to the experiments. The bugs preferred herbivore‐damaged to clean guava, and showed a slight preference for damaged to clean eucalyptus. These results may explain the lack of impact of predatory arthropods on herbivore populations on eucalyptus and suggests that eucalyptus may offer an enemy‐free space for herbivores.  相似文献   

10.
11.
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.  相似文献   

12.
Sown wildflower strips are increasingly being established in Europe for enhancing arthropod conservation and the provision of ecosystem services, including biotic pollination and natural pest control. Here we use floral traits to identify different plant functional effect groups. Floral resources were provided in four experimental levels characterised by a cumulatively increasing flower trait diversity and vegetation stand complexity. The first level consisted of a bare control strip, whilst in each subsequent level three wildflower species with different functional traits were added (Level 0: control; Level 1: three Apiaceae species; Level 2: three Apiaceae and three Fabaceae species; Level 3: three Apiaceae, three Fabaceae species, and Centaurea jacea (Asteraceae), Fagopyrum esculentum (Polygonaceae), Sinapis alba (Brassicaceae)). Plots with sown wildflower strip mixtures were located adjacent to experimental plots of organically-managed tomato crop, which is attacked by multiple pests and partially relies on bees for fruit production, and hence dependent on the provision of pollination and pest control services. Results obtained here show that the inclusion of functionally diverse wildflower species was associated with an augmented availability of floral resources across time, and this increased the abundance of bees and anthocorids throughout the crop season. Several natural enemy groups, such as parasitoids, coccinelids and ground-dwelling predators, were not significantly enhanced by the inclusion of additional flower traits within the strips but the presence of flower resources was important to enhance their conservation in an arable cropping system.  相似文献   

13.
Establishing wildflower strips has been suggested as an effective measure to promote pollination services, pest control or general insect biodiversity, but little is known about the integration of these different objectives when selecting flower seed mixtures. In ten agricultural landscapes in the Netherlands, we established a wildflower strip (0.4 – 4.9 ha) with half of each strip sown with a mixture targeting longer-tongued pollinators and the other half sown with a mixture targeting shorter-tongued pollinators and natural enemies. We determined establishment success of sown wildflowers and evaluated the attractiveness of the established flower communities to multiple functional groups of flower visitors: bumblebees (long-tongued pollinators), hoverflies (short-tongued pollinators and natural enemies), and butterflies and total flower-visitor richness (indicators of wider biodiversity values). Bumblebees clearly preferred the pollinator-targeted seed mixture and were positively associated with cover of Fabaceae and negatively with Apiaceae. Hoverflies consistently preferred the natural enemy mixture and were positively associated with Apiaceae. The other target groups displayed no clear responses to seed mixture type but instead were associated with local flower richness within strips. Across sites, responses of flower-visitors to sown mixture types did not depend on wildflower strip size, proportion of surrounding semi-natural habitat, or flower variables. However, all flower-visitors except butterflies increased with increasing established cover or richness of (sown) flower species across sites. Our results suggest that, although species-rich wildflower strips may benefit several species groups, maximising different objectives involves trade-offs between functional groups that prefer short- or long-corolla flowers. Furthermore, our study suggests that sowing a wildflower mixture does not necessarily result in a vegetation with the same composition as the seed mixture as species may establish poorly or not at all. Selection of flower species for seed mixtures should therefore, in addition to insect target group, take the establishment characteristics of plant species into account.  相似文献   

14.
Abstract:  Apparent competition, mediated by a shared predator, plays a key role in conservation biological control. Appropriate agroecosystems management may favour this type of indirect interaction. In that context, our aim was to test the effect of rose bush [ Rosa rugosa (Thunb.)] strips on the building up of aphid populations and of their natural enemies in adjacent cereal habitats. Several aphid species are currently found on Rosa sp. including Metopolophium dirhodum (Walker) for which it is a primary host. Aphid predators and parasitoids may build their populations on the aphid population present on Rosa sp. and later on migrate to wheat field during the cereal aphid infestation. Moreover, the flowers of the rose bushes may provide a source of nectar and pollen to these natural enemies. Our experiment was conducted in three rose margin wheat plots with a strip of rose bushes of R. rugosa and three control plots. Plots were compared during 2 years (2003 and 2004). Aphid, parasitoid and predator densities were recorded from May to the harvest of wheat on rose bushes and in wheat. In 2003, the aphid densities were moderate but in 2004, the population of aphid was very high. Even if predator and parasitoids arrived earlier in rose margin field than in control ones, the presence of rose bushes did not influence the aphid population within the field. Metopolophium dirhodum did not seem to migrate from the rose bushes to wheat. The level of parasitism was weak in rose bushes and the natural enemy population was not different in rose margin wheat and in control plots. The causes of the lack of efficiency of this type of management are discussed as well as the high aphid population in wheat in 2004.  相似文献   

15.
Direct and indirect effects of plant genetic variation on enemy impact   总被引:4,自引:0,他引:4  
Abstract.
  • 1 The Tritrophic and Enemy Impact concepts predict that natural enemy impact varies: (a) among plant genotypes and (b) may depend on the abundance of heterospecific herbivores, respectively. I tested these predictions using three herbivore species on potted, cloned genotypes of Salik sericea Marshall in a common garden experiment.
  • 2 Densities of the leaf miner (Phyllonorycter salicifoliella (Chambers)) and two leaf galling sawflies (Phyllocolpa nigrita (Marlatt) and Phyllocolpa eleanorae Smith and Fritz) varied significantly among willow clones, indicating genetic variation in resistance.
  • 3 Survival and natural enemy impact caused by egg and larval parasitoids and/or unknown predators differed significantly among willow clones for each of the three herbivore species, indicating genetic variation in survival and enemy impact.
  • 4 Survival of Phyllonorycter was negatively density-dependent among clones.
  • 5 Survival of Phyllonorycter and Phyllocolpa eleanorae were positively correlated with densities of heterospecific herbivores among clones and parasitism of these species were negatively correlated with densities of the same heterospecific herbivores among clones.
  • 6 At least for Phyllonorycter this positive correlation may suggest either facilitation of survival between herbivore species, which do not share natural enemies, or an apparent interaction caused by host plant genetic variation.
  • 7 Among clones, egg parasitism of Phyllocolpa eleanorae was weakly positively correlated with density of Phyllocolpa nigrita. Since these species share the same Trichogramma egg parasitoid, this interaction could support the hypothesis of apparent competition.
  相似文献   

16.
Inbreeding can profoundly affect the interactions of plants with herbivores as well as with the natural enemies of the herbivores. We studied how plant inbreeding affects herbivore oviposition preference, and whether inbreeding of both plants and herbivores alters the probability of predation or parasitism of herbivore eggs. In a laboratory preference test with the specialist herbivore moth Abrostola asclepiadis and inbred and outbred Vincetoxicum hirundinaria plants, we discovered that herbivores preferred to oviposit on outbred plants. A field experiment with inbred and outbred plants that bore inbred or outbred herbivore eggs revealed that the eggs of the outbred herbivores were more likely to be lost by predation, parasitism or plant hypersensitive responses than inbred eggs. This difference did not lead to differences in the realized fecundity as the number of hatched larvae did not differ between inbred and outbred herbivores. Thus, the strength of inbreeding depression in herbivores decreases when their natural enemies are involved. Plant inbreeding did not alter the attraction of natural enemies of the eggs. We conclude that inbreeding can significantly alter the interactions of plants and herbivores at different life-history stages, and that some of these alterations are mediated by the natural enemies of the herbivores.  相似文献   

17.
Monocultures typical of intensive agriculture offer ideal conditions to specialized herbivores while depriving their natural enemies of habitat and nutritional resources. The resulting release of herbivores from both bottom-up and top-down control causes pest outbreaks in economically important crops. Boosting locally occurring natural enemy populations through species-specific habitat management to restore natural herbivore control has been much advocated but remains rarely tested in the field. Here, we investigated whether adding specifically selected flowering plants to monocultures increases parasitation rates of herbivores and crop yield. We performed replicated field experiments in 2 years and found that adding cornflowers (Centaurea cyanus) into cabbage (Brassica oleracea) fields significantly increased larval and egg parasitation and egg predation of the herbivore, reduced herbivory rates, and increased crop biomass in at least 1 year. These findings show that addition of a single, well-chosen flowering plant species can significantly increase natural top-down pest control in monocultures but success is variable. This is relevant on two applied levels. First, well chosen companion plants may partially substitute pesticides in agriculture if the approach is optimized, reducing negative effects such as unspecific killing of non-target organisms, residues in food, contamination of soils and water-bodies and increasing pesticide resistances. Our results suggest that, from an agro-economical point of view, egg parasitoids or predators may be the best targets for habitat management because strong natural selection acts on larval parasitoids to keep their hosts alive for their own development. Second, the addition of non-crop vegetation to monocultures benefits biodiversity conservation directly through resource diversification and indirectly through the reduction of pesticide application that increased natural control makes possible.  相似文献   

18.
Ephemeral cropping systems are characterized by frequent disturbances of ecological processes, which may compromise the conservation of plant and arthropod diversity and the ecosystem services they may provide. Conservation biological control practices include habitat manipulations that provide non‐pest resources and selectively enhance natural enemies' effectiveness. This study, conducted in eight commercial fields of organically grown tomato, compared the effectiveness of sown flower strips with semi‐natural margins in regulating natural enemy abundance, biocontrol, and crop damage. During repeated visits, the abundance of different arthropod groups was recorded. Crop surveys included measurement of aphid abundance, parasitism, and leaf and fruit damage from sap‐sucking and lepidopteran pests. Semi‐natural habitats were associated with higher vegetation diversity, but natural enemies were more strongly associated with sown strips during flowering. Sap‐sucking pests were always recorded in higher abundance in flower strips, but crop damage in the plots adjacent to these strips was lower, suggesting that these strips may act as a trap‐crop. The inclusion of floral supplements enhanced the parasitism rate of aphids in the crop, and reduced the rate of increase of lepidopteran‐caused foliar damage with time. Early in the growing season, semi‐natural strips showed significantly lower levels of crop damage and aphid counts, suggesting that these habitats may be important during early crop colonization by natural enemies. These results indicate that the inclusion of flower strips enhances the conservation of arthropod functional diversity in ephemeral crops, and that diverse mechanisms are important for controlling different pests. However, the efficacy of habitat manipulation is likely to be greater when it is complemented with the conservation of diverse semi‐natural vegetation in the pre‐existing field margin.  相似文献   

19.
Reducing the use of insecticides is an important issue for agriculture today. Sowing wildflower strips along field margins or within crops represents a promising tool to support natural enemy populations in agricultural landscapes and, thus, enhance conservation biological control. However, it is important to sow appropriate flower species that attract natural enemies efficiently. The presence of prey and hosts may also guide natural enemies to wildflower strips, potentially preventing them from migrating into adjacent crops. Here, we assessed how seven flower traits, along with the abundance of pollen beetles (Meligethes spp., Coleoptera: Nitidulidae) and true weevils (Ceutorhynchus spp., Coleoptera: Curculionidae), affect the density of parasitoids of these two coleopterans in wildflower strips sown in an oilseed rape field in Gembloux (Belgium). Only flower traits, not host (i.e. pollen beetles and true weevils) abundance, significantly affected the density of parasitoids. Flower colour, ultraviolet reflectance and nectar availability were the main drivers affecting parasitoids. These results demonstrate how parasitoids of oilseed rape pests react to flower cues under field conditions. Similar analyses on the pests and natural enemies of other crops are expected to help to develop perennial flower mixtures able to enhance biological control throughout a rotation system.  相似文献   

20.
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