Tailoring complexity. Multitrophic interactions in simple and diversified habitats
Keywords: vegetational diversity, intercropping, plant quality, herbivores, D. semiclausum, foraging behaviour, time-allocationReduction of herbivore populations is more often observed in vegetationally diverse than in simple ecosystems. Consequently, plant-species mixtures (i.e. intercropping) may be used to manage pest problems in agro-ecosystems, thereby contributing to the development of ecologically sustainable crop production. Compared with monotypic stands, increasing vegetation diversity may suppress herbivore populations through the reduction in the apparency and quality of crop plants and by the increased success of natural enemies. Unfortunately, the highly variable responses of both herbivores and natural enemies to intercropping provide insufficient information to make generalisations for the selection of pest-suppressive plant-mixtures. An explanation for this lack of information is that predictions of the hypotheses explaining the pest-suppression are relevant at the population level, while the underlying mechanisms at the behavioural (i.e. functional) level remain largely untested. In this thesis I attempted to further our understanding of how vegetation diversity leads to pest suppression in agro-ecosystems. The aims were (1) to understand the cause(s) of lower herbivore numbers in vegetationally more diverse cropping systems compared to monocultures and (2) to study the behavioural bases of the responses of natural enemies to vegetation diversity. The studied system includedBrusselssprout ( Brassica oleracea gemmifera), its herbivores, and Diadegma semiclausum , a parasitoid of the diamondback moth. Vegetational diversity was characterised by mixingBrusselssprout with either barley ( Hordeum vulgare ) or mustard ( Sinapisalba ). Numbers of several herbivore species were reduced when Brussels sprout was mixed with barley. A study showed that the plant competition in the species mixture influenced herbivore responses by altering plant quality compared with the monocrop. Field and simulation studies showed that responses of herbivores in diversified habitats were influenced by species-related differences in foraging behaviour. Behavioural and analytical studies showed the importance of inter- and intraspecific variation in volatiles of both damaged and undamaged plants in the attraction of the parasitoid D. semiclausum . Plant mixtures interacted with the searching behaviour and time-allocation of wasps. Compared with pureBrusselssprout patches, mustard attracted and retained individuals longer, whereas barley reduced their tendency to enter the plant patch. Although both mustard and barley reduced the tendency of wasps to locate hosts onBrusselssprout, parasitoids improved their foraging efficiency through oviposition experiences and became equally efficient in finding further hosts. In conclusion, this thesis demonstrates the importance of foraging behaviour in explaining variable responses of herbivores and parasitoids to plant-species mixtures.
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| Format: | Doctoral thesis biblioteca |
| Language: | English |
| Subjects: | biological control, feeding behaviour, herbivores, host parasite relationships, insect pests, interactions, intercropping, natural enemies, parasitoids, plants, trophic levels, vegetation types, biologische bestrijding, gastheer parasiet relaties, herbivoren, insectenplagen, interacties, natuurlijke vijanden, parasitoïden, planten, trofische graden, tussenteelt, vegetatietypen, voedingsgedrag, |
| Online Access: | https://research.wur.nl/en/publications/tailoring-complexity-multitrophic-interactions-in-simple-and-dive |
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| Summary: | Keywords: vegetational diversity, intercropping, plant quality, herbivores, D. semiclausum, foraging behaviour, time-allocationReduction of herbivore populations is more often observed in vegetationally diverse than in simple ecosystems. Consequently, plant-species mixtures (i.e. intercropping) may be used to manage pest problems in agro-ecosystems, thereby contributing to the development of ecologically sustainable crop production. Compared with monotypic stands, increasing vegetation diversity may suppress herbivore populations through the reduction in the apparency and quality of crop plants and by the increased success of natural enemies. Unfortunately, the highly variable responses of both herbivores and natural enemies to intercropping provide insufficient information to make generalisations for the selection of pest-suppressive plant-mixtures. An explanation for this lack of information is that predictions of the hypotheses explaining the pest-suppression are relevant at the population level, while the underlying mechanisms at the behavioural (i.e. functional) level remain largely untested. In this thesis I attempted to further our understanding of how vegetation diversity leads to pest suppression in agro-ecosystems. The aims were (1) to understand the cause(s) of lower herbivore numbers in vegetationally more diverse cropping systems compared to monocultures and (2) to study the behavioural bases of the responses of natural enemies to vegetation diversity. The studied system includedBrusselssprout ( Brassica oleracea gemmifera), its herbivores, and Diadegma semiclausum , a parasitoid of the diamondback moth. Vegetational diversity was characterised by mixingBrusselssprout with either barley ( Hordeum vulgare ) or mustard ( Sinapisalba ). Numbers of several herbivore species were reduced when Brussels sprout was mixed with barley. A study showed that the plant competition in the species mixture influenced herbivore responses by altering plant quality compared with the monocrop. Field and simulation studies showed that responses of herbivores in diversified habitats were influenced by species-related differences in foraging behaviour. Behavioural and analytical studies showed the importance of inter- and intraspecific variation in volatiles of both damaged and undamaged plants in the attraction of the parasitoid D. semiclausum . Plant mixtures interacted with the searching behaviour and time-allocation of wasps. Compared with pureBrusselssprout patches, mustard attracted and retained individuals longer, whereas barley reduced their tendency to enter the plant patch. Although both mustard and barley reduced the tendency of wasps to locate hosts onBrusselssprout, parasitoids improved their foraging efficiency through oviposition experiences and became equally efficient in finding further hosts. In conclusion, this thesis demonstrates the importance of foraging behaviour in explaining variable responses of herbivores and parasitoids to plant-species mixtures. |
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