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Pest‐regulating natural enemies often require crop and non‐crop habitats to persist and be effective. These habitats offer hibernation sites, alternative prey or floral resources but can also be complementary in when they provide resources. The relative contribution of these different habitats to the performance of pest‐regulating insects is largely unknown, since it is difficult to study empirically. Landscape‐based population‐dynamical modelling can fill this research gap. In this study, we modelled the dynamics of predatory hoverflies (Diptera: Syrphinae) and their aphid prey in a collection of habitats. These hoverflies are dependent on different habitats for different reasons. While their larvae predate on aphids, adult hoverflies require floral resources. Resources are often segregated in different habitats. In addition, they are only temporarily available in any habitat type. In our model, hoverflies move between different habitats and select where to feed and where to produce off‐spring based on optimal foraging considerations. The model represents habitats common in arable landscapes and their temporal availability of resources is parameterized based on field observations. The model shows that effective pest suppression will only occur in the presence of at least three different habitats, including two crops that provide prey resources at different times of the year. A woody habitat with shrubs and trees provide aphid prey very early and late in the season, whereas an early crop and a late crop cover the period in between. In addition, these habitats need to provide floral resources in the same period as aphids, for example by flower strips in the margins of crop fields or blossoming trees or shrubs in the woody habitat. Under the model assumptions, the best pest suppression is obtained when the woody habitats take up 6% to 10% of the landscape. In addition to yearly population fluctuations, also bi‐ or multi‐yearly cycles may occur, depending on the composition of the landscape. Synthesis and applications. Our model shows when an agricultural landscape is ‘complete’ for natural enemies (and for effective pest control). For this, it needs to contain multiple habitats that supply floral and prey resources in different periods of the year. [ABSTRACT FROM AUTHOR]

In modern agricultural landscapes, many organisms providing ecosystem services such as pollination and natural pest control are likely constrained by shortage of nectar and/or pollen required for adult nutrition. More and more flower-rich field margin strips and other habitats are created to eliminate these constraints. For most target organisms, however, it is not well known which (types of) flowers are effective in providing suitable pollen and nectar., We studied the suitability of a wide range of flowers as a food source for zoophagous hoverflies (hoverflies with predatory larvae) at five different levels: nectar accessibility (based on flower morphology), realized adult fitness, flower choice (both based on cage experiments), flower visitation and hoverfly abundance in mixed vegetation (both based on field observations)., Realized survival of Episyrphus balteatus is related to effective flower depth by a sigmoid function. The critical flower depth is 1·6 mm, which is less than the proboscis size of the hoverfly. For Asteraceae, the critical floret depth is even less than 1·0 mm, which - in contrast to common knowledge - rules out most species within this family., Both flower choice in the laboratory and flower visitation rates in the field are well correlated with nectar accessibility and realized adult survival., In mixed floral vegetation, the number of zoophagous hoverflies is highly correlated with the abundance of only those flowers that have accessible nectar for these hoverflies., Synthesis and applications. This comparative study demonstrates that nectar (and not pollen) accessibility is the main driver determining flower resource suitability, flower choice and abundance of zoophagous hoverflies in arable field margins. The study identifies the limited range of plant species that can effectively support these beneficial insects. Preserving the right flowers in and around agricultural fields could enhance local populations and the pest control and pollination services they provide. [ABSTRACT FROM AUTHOR]