Host-plant mediated effects of root herbivory on insect seed predators andtheir parasitoids

The effects of root herbivory on a tephritid seed predator (Terellia rufica uda) and its parasitoids were investigated. Soil fauna were manipulated by insecticide treatment; host plant (Cirsium palustre) phenology and the ovip osition behaviour of both tephritid and parasitoids (Pteromalus elevatus an d Torymus chloromerus) recorded. Although insecticide-treated land hence re duced root herbivory) plants had larger flowerheads, population abundances of both tephritids and parasitoids were greater on thistle plants subjected to root herbivory. Percentage parasitism was similar in both treatments. R oot herbivory is thought to enhance the nutrient quality of plants and this may have resulted in the tephritid preferentially feeding on thistles whos e roots had been attacked. Parasitoids on these plants were probably affect ed by a combination of increased plant attractivity las for the tephritids) , smaller flowerheads aiding ovipositor entry and more tephritid hosts bein g present. This is the first study to show that root herbivores, through pl ant-mediated interactions, can affect seed herbivores and also, albeit indi rectly through the host, natural enemy trophic levels.