Labeling an Egg Parasitoid, Anagrus epos (Hymenoptera: Mymaridae), with Rubidium within an Overwintering Refuge

Abstract

French prune trees provide overwintering habitat for the egg parasitoid Anagrns 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 RbCI 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, Edwanuiana prnnicola 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 RbCI. This is 3.9 times the background level and indicates successful labeling of overwinteringA. epos. However, there was substantial overlap in rubidium content between A. epos from treated trees and those from untreated sites. A. epos reared from rubidiumenriched host eggs and maintained in the lab on a mixture of honey and water e1iliibited 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.

Timing, Magnitude, Rates, and Putative Causes of Predator Movement Between Cotton and Grain Sorghum Fields

“…Rubidium is a ubiquitous element chemically similar to potassium but usually found at very low concentrations. This similarity allows rubidium to be incorporated into biological systems at moderate levels without harmful effects (Stimmann 1974, Knight et al 1989, Johnson and Reeves 1995 and results in its vertical transmission between trophic levels (Graham et al 1978, Johnson and Reeves 1995, Corbett et al 1996. These properties permit augmentation of background rubidium levels to internally mark plants, herbivores, and natural enemies.…”

Caste differences in feeding and trophallaxis in the western drywood termite, Incisitermes minor (Hagen) (Isoptera, Kalotermitidae)

“…It was an excellent marker because ingestion of Rb did not have an adverse effect on survival of nymphs at concentrations between 1000 and 5000 ppm, was not immediately excreted and was retained in the tissues at detectable levels for up to two weeks. Rb has also been used in a variety of insect feeding and dispersal studies (Van Steenwyk, 1978;Holbrook et al, 1991;Holbrook, 1995;Corbett et al, 1996;Woods and Streett, 1996 a, b;Coll et al, 1997;Woods et al, 1997).…”

Use of Rubidium to Label Lysiphlebus testaceipes (Hymenoptera: Braconidae), a Parasitoid of Greenbugs (Homoptera: Aphididae), for Dispersal Studies

“…The authors reported that the parasitoids fed on diets containing 500 or 1,000 ppm ofRbCI were labeled up to 4 d after emergence. Corbett et al (1996) reported minimal decay of Rb levels in labeled Anagrus epos Girault adults, but this mymarid did not live >72 h after adult emergence.…”

“…Parasitoid labeling with Rb was also accomplished by Corbett et al (1996), Jackson et al (1988), Jackson andDebolt (1990), andHopper (1991) with other hymenopteran species, whereas Guillebeau et al (1993) labeled another aphid species.…”