Which shrubs and trees can conserve natural enemies of aphids in spring?

Habitats with shrubs and trees within the agricultural landscape may contribute to the maintenance of natural enemies of pests. Aphids and flowers are important resources for beneficial natural enemies such as ladybeetles, hoverflies and lacewings. Woody plants are the most likely candidates to provide these resources in spring, as they are among the first to develop aphid colonies as well as flowers. To evaluate their possible contribution, 19 species have regularly been sampled in four consecutive springs on presence of flowers and on numbers and nature of aphids and their natural enemies. The species show large differences in flowering period and in numbers of aphids. Species that develop high numbers of aphids generally show the highest numbers of ladybeetles and hoverflies, while the number of ladybeetles is also related to the presence of flowers. Aphid species are with few exceptions identified as unharmful for agriculture. The preliminary top 5 of species recommended for planting are: sycamore maple spindle, hazel, blackthorn and grey willow, as it provides a sufficient spread in floral and prey resources for natural enemies in spring

Natural pest control requires a complete landscape

In many studies on landscape and functional biodiversity it is assumed that pest-regulating insects require other habitats than only agricultural fields. Other habitats can e.g. be important as hibernation site, as source of alternative prey or as source of floral resources. The relative contribution of the different habitats to the performance of the beneficial insects and to pest-regulating services they provide is very difficult to study empirically. Landscape-based population-dynamical modelling can then come at hand. Such models can be used to predict mechanisms and patterns that can be tested experimentally. As an example, I created population models of aphid-feeding hoverflies moving between different habitats in an arable landscape. The models are designed and parameterised on the basis of field observations on temporal and habitat-related availability of resources. Habitat-structured models can indicate the optimal composition of the landscape with respect to pest control. The models e.g. indicate that the amount of woody elements, which are particularly important for hoverflies as spring habitat, are a likely a bottleneck for effective pest regulation in Dutch arable landscapes. They also show that various arable crops can enhance each other’s pest control when their aphid populations peek at different moments in time (such as winter wheat and potato). These and other habitats are complementary in their function for the predators, and several of them are needed to create a ‘complete landscape’