The value of three cereal aphid species as food for a generalist predator

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Abstract
Summary: The value of the cereal aphid speciesMetopolophium dirhodum(Wlk.), Sitobion avenae(F.) andRhopalosiphum padi(L.) as prey for the linyphiid spiderErigone atra(Bl.) was assessed. Fecundity of females was determined for spiders fed on eight experimental diets: three single‐species aphid diets, a mixed diet of all three aphid species, three mixed diets with each aphid species in combination with fruit fliesDrosophila melanogaster(Meig.), and pureD. melanogasteras a high quality comparison diet. The development and survival of first‐instar juveniles fed on three diets of single aphid species, and on a diet of Collembola were compared with those subjected to starvation. Prey value for adult females was assessed by egg production, hatching success and offspring size.In pure diets all three aphid species were of low value to the spiders, causing a rapid decline in egg production and supporting no growth of significance of first‐instar juveniles. No difference in value of aphid species of single‐species aphid diets was found in the fecundity experiment, while a ranking of aphid species ofM. dirhodum> R. padi> S. avenaewas revealed in the survivorship experiment. A mixed‐aphid diet was not found to be advantageous compared with single‐species aphid diets, and no advantage of including aphids in mixed diets with fruit flies was found.Metopolophium dirhodumandR. padiwere neutral in mixed diets, while a diet ofS. avenaeand fruit flies caused reduced egg production compared with the pure diet of fruit flies, revealing a toxic effect ofS. avenaeon the spider. The value‐ranking of aphid species in mixed diets was similar to that of single‐species diets. A similar ranking of aphid species was found for different fitness parameters (fecundity of adult females and development of juveniles).A ranking of aphids by offspring size of mothers on aphid‐only diets wasS. avenae> M. dirhodum> R. padi. All aphid‐fruit fly diets resulted in larger offspring than a diet of onlyD. melanogaster, with the overall largest offspring being produced on the diet ofM. dirhodumand fruit flies.