Effect of flowering plant strips on aphid and syrphid populations in lettuce

A two-year field experiment was carried out in Southeast Spain to study the effect of planting strips of Coriandrum sativum L. or Chrysanthemum coronarium L. with spring Iceberg lettuce on aphid and syrphid predator populations. Without chemical treatments, infestations by Nasonovia ribisnigri Mosley spread over the field in March and April. In 2001, the severity of infestations was greater (statistically significant) in lettuces from the plot with coriander margins in comparison with the monoculture. In 2002, predatory syrphid larvae were more abundant (tendency not statistically significant) on lettuces from the plot with flowering plant strips (1.9 larvae/head) than on lettuce monocultures (1.3 larvae/head). Adult syrphids were foraging on flowering strips from early winter to spring. Species identified being: Episyrphus balteatus De Geer, Eupeodes corollae Fabricius, Sphaerophoria rueppellii Wiedemann and Sphaerophoria scripta Linnaeus.