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.