Labeling an egg parasitoid, Anagrus epos (Hymenoptera: Mymaridae), with rubidium within an overwintering refuge

French prune trees provide overwintering habitat for the egg parasitoid Anagrus epos Girault (Hymenoptera: Mymaridae), an important natural enemy of the the grape leafhopper, Erythroneura elegantula Osborn (Homoptera: Cicadellidae). French prune trees were treated with rubidium during the fall of 1991-1993 to assess the potential for obtaining an elemental label in overwintering A. epos. Multiple applications of 5,000-ppm solutions of RbCl to French prune foliage from late August to early October resulted in increases in foliar rubidium content of up to 200 times the naturally occuring concentration. Rubidium content of adult prune leafhoppers, Edwardsiana prunicola Edwards (Homoptera: Cicadellidae), collected from treated trees was up to 130 times the naturally occurring level. Naturally occuring rubidium content of A. epos was 0.052 ng Rb per individual based on a sample of 498 wasps collected from 3 separate, untreated grape vineyards. Mean rubidium content was 0.205 ng Rb in A. epos collected in the spring directly from French prune trees that had been treated in the fall with RbCl. This is 3.9 times the background level and indicates successful labeling of overwintering A. epos. However, there was substantial overlap in rubidium content between A. epos from treated trees and those from untreated sites. A. epos reared from rubidium-enriched host eggs and maintained in the lab on a mixture of honey and water exhibited minimal decay of the elemental label during the adult lifetime. Success of this labeling approach has made possible the direct study of the dispersal of A. epos from treated French prune tree refuges into adjacent grape vineyards.