The role of the perennial stinging nettle, Urtica dioica, as a reservoir of beneficial natural enemies

A wide range of natural enemies, including predators, parasites and entomophagous fungi were observed to feed on the stinging nettle aphid, Microlophium carnosum, populations of which increased rapidly in late April and early May. Patches of stinging nettles thus served as an important alternate feeding site for some beneficial natural enemies before pest aphids appeared on cultivated plants. Anthocoridae, Miridae and Coccinellidae were the most abundant specific predators sampled on nettles; only the Coccinellidae appeared to disperse over a defined period to other habitats. The hymenopterous parasites Aphidius ervi and Ephedrus lacertosus parasitized up to 10% of M. carnosum populations in June: two species of the fungus Entomophthora occurred spasmodically. Cutting patches of nettles in May or June had the most striking effect on the species and numbers of Coccinellidae. Cutting in mid-June might increase the numbers and impact of natural enemies on nearby pest infestations.