Beneficial associations between aphid natural enemies and noncrop plants inhabiting lettuce field margins

Field margins composed by noncrop plants are important in annual cropping systems occurring in the Central region of Spain as reservoirs of natural enemies of aphid pests. Field margins adjacent to a lettuce crop were sampled to identify noncrop plants that act as reservoirs for entomopathogenic fungi and as floral resources for hoverflies. The survey conducted in Spring 2007 and 2008 included natural enemies occurring in a lettuce crop, natural vegetation present in field margins as well as selected flowering plants artificially introduced as monospecific patches to attract aphidophagous hoverflies. Pandora neoaphidis was the most abundant entomopathogenic fungi found attacking several aphid species (Acyrthosiphon lactucae, Aulacorthum malvae, Metopolophium festucae and Rhopalosiphum padi) present on Malva sylvestris Sylibum marianum, Myosotis arvensis and Hordeum murinun. Aphids were found infected by P. neoaphidis on noncrop plants in mid-March, two weeks earlier than infections were detected on lettuce aphids. Initial infections by P. neoaphidis on aphid species colonizing lettuce were recorded on plants located in the first rows of the crop, close to this field margin, suggesting the importance of field margins for the beginning of epizootics of P. neoaphidis on lettuce aphids. Hoverfly larvae preying on lettuce aphid were first detected in mid-April. Coriandrum sativum, Diplotaxis catolica, Calendula officinalis, Hirschfeldia incana, Tagetes patula and Pimpenella anissum were the flowering plants most attended by adult hoverflies among the 28 species tested