Eggsac parasitism of money spiders (Araneae, Linyphiidae) in cereals, with a simple method for estimating percentage parasitism ofErigonespp. eggsacs by Hymenoptera

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Abstract
Observations on parasitism of eggsacs of the linyphiid spidersErigonespp.,Oedothoraxspp.,Bathy‐phantes gracilisandLepthyphantes tenuisby four species of hymenopterous parasitoids in a field of winter wheat are described. The dominant parasitoids emerging from eggsacs wereGelis festinans(Ichneumonidae) andBaeussp. (Scelionidae). Percentage parasitism of introduced and naturally occurring eggsacs was compared for the months of May, June and July. No eggsacs ofOedothoraxspp. andB. graciliswere parasitized.Oedothoraxspp. females were observed, in both laboratory and field, to guard their eggsacs efficiently against attack by parasitoids. The percentage of naturally occurring eggsacs ofErigonespp. parasitized byG. festinanswas not significantly different from the percentage parasitism of eggsacs introduced into the field in modified Petri dishes; the Petri dish introduction method therefore provides a simple and efficient means of assessing parasitism in the field.