MARKING APHIDS AND THEIR PARASITES WITH ¹⁴C IN FIELD STUDIES

Abstract

Aphids (Brevicoryne brassicae (L.) and Myzus persicae (Sulzer)) were marked with 14C by feeding them on host plants (rape, Brassica napus L. var. oleifera and kale, Brassica oleracea L. var. acephala (D.C.) Alef.) which had been exposed to 14CO2. With concentrations of radioactivity in the leaves of 20–50 μCi per g wet weight, the adult aphids contained 5–10nCi* of 14C after 2 days' feeding. The concentration of activity in the leaves decreased with a half‐life of 6–12 days depending on the age of the leaves. The aphids lost much of their activity after removal to an unlabelled plant, retaining 20% of the initial activity after 8 days. The first progeny born had an activity of 3% of the initial activity of the parents, and those born after 8 days, 0.08%. The progeny retained 70% of this activity as adults. Parasites (Diaeretiella rapae (M'Intosh)) contained 2–4 nCi after developing from egg to adult in aphids labelled with 4–30nCi. Adult parasites contained 0.3nCi after feeding on labelled honey dew. In a field trial, marked aphids and parasites were identified amongst insects caught at 0.6 m and 6 m from a labelled plant. Also marked were the hyperparasites Alloxysta brassicae (Ashmead) and Pachyneuron aphidis (Bouché). RÉSUMÉ MARQUAGE DE PUCERONS ET DE LEURS PARASITES AVEC DU 14C DANS DES ÉTUDES SUR LE TERRAIN On a marqué avec du 14C les pucerons Brevicoryne brassicae (L.) et Myzus persicae (Sulzer) en les nourrissant sur des plantes hôtes Brassica napus L. var. oleifera et Brassica oleracea L. var. acephala (D.C.) Alef. exposées au 14CO2. La concentration de radioactivité dans les feuilles diminuait à la longue, la demi‐vie biologique de l'isotope étant de 6 jours dans les feuilles jeunes et de 12 jours dans les feuilles mûres. Il n'y avait pas beaucoup de perte de 14C dans la plante entière pendant 2 mois, ce qui était indiqué par l'activité des pucerons qui se nourrissaient sur la plante à la fin de ce temps. Pour une concentration de radioactivité de 20–50 μCi g−1 dans les feuilles, l'activité des pucerons adultes était de 5–10 n Ci après 2 jours de nourrissement. Les pucerons perdaient beaucoup de leur activité après avoir été transportés sur une plante non‐marquée, retenant 20% de la valeur initiale après 8 jours. Beaucoup d'activité perdue fut retrouvée dans des descendants marqués; ceux qui naquirent les premiers ayant une activité égale à 3% de l'activité initiale des parents; ceux qui naquirent 8 jours plus tard, de 0.08%. Les descendants retenaient 70% de cette activité comme adultes. La reproduction ne fut pas affectée si les parents contenaient 5 n Ci. Des parasites (Diaeretiella rapae (M'Intosh)) furent marqués de 2–4 nCi après développement d'œuf jusqu'à adulte dans des pucerons marqués de 4–30 nCi. Des parasites adultes furent marqués de 0.3 n Ci en les nourissant du miellat excrété par ces pucerons. Dans un essai sur le terrain, une plante marquée dans le champ fut attaquée par des pucerons des deux espèces. Les insectes furent attrapés dans des pièges à succion placés à des distances de 0.6 m ...

15N‐marked aphids for predation studies under field conditions

“…second trial; after 10 days on 15 N-enriched seedlings), the rate of 'dilution' of 15 N was much lower (time constant 5.5 days). Nevertheless, in both trials 15 N most probably has been also lost in aphids due to 15 N-transfer to the offspring, as described for bugs (Odum & Golley, 1963), other aphid species (Robertson, 1976) and in 'multigenerational marking' (i.e., production of marked offspring by marking their parents) (McDaniel & Sterling, 1979;Hayes, 1991). As confirmation, we also found in our experiments that offspring of 15 N-marked aphids became 15 N-marked, although to a lower extent than adults (personal observation).…”

“…After transferring the aphids to non-enriched seedlings, their 15 N-content decreased exponentially. Exponential decay was already described for other marker substances (Hubbell et al, 1965;Robertson, 1976), but in contrast to these data the 15 N-content did not fall to or below the natural level of 15 N. Additionally, although the constant 15 N-content phase was reached after different time periods in the two trials (time constant of 1.54 and 5.5 days, respectively), it is remarkable that the final levels of 15 N in both experiments were quite similar after the decay phase (3.68 and 4.20 atom % 15 N).…”

“…ELISA) and electrophoresis have been used to study predation in the field (Sunderland, 1987;Powell et al, 1996). Another approach for this kind of studies has been the marking of prey with radioactive isotopes or elements like rubidium and the subsequent tracing of these labels in the food chain (Robertson, 1976;Mc Daniel & Sterling, 1979;Breene & Sterling, 1988;Hayes, 1991;Johnston & Reeves, 1995).…”

Quantifying aphid predation rates of generalist predators in the field

“…Although the labelling of aphids with radioactive phosphorous has indicated the extent of its uptake by parasitoids (Robertson, 1976) and the dispersal of virulous aphids in sugar beet (Bjorling et al, 1951), there is only one study documenting its application for quantifying aphid predation (Pendleton & Grundman, 1954). The thistle Cirsium undulatum (Nutt.)…”

Invertebrate predation of 15N‐marked prey in semi‐field wheat enclosures

“…A different approach towards the study of predation is the release of marked prey organisms, and a subsequent analysis of their marker content in predators. Markers that have been used previously are radioactive isotopes (Robertson, 1976; McDaniel & Sterling, 1979; Breene & Sterling, 1988), rare elements such as Rubidium or Dysprosium‐164 ( Hayes, 1991; Johnson & Reeves, 1995), and immunoglobulines (Hagler & Durand, 1994). Depending on the marker being used, effects on the marked organisms could not be avoided (Frazer & Raworth, 1974; Wölkerling & Schmidt, 1987).…”