N-15-marked aphids for predation studies under field conditions

Individuals ofSitobion avenae (F.) (Homoptera: Aphididae) were marked with the stable isotope N-15 through feeding on cereal seedlings which were imme rsed in a N-15-enriched nutrient solution. Increased N-15-contents were obt ained in all aphids with no detrimental effect on survival and fertility. W hen N-15-marked aphids were transferred to non N-15-enriched seedlings, aft er a short initial decreasing phase, N-15-contents remained nearly constant in time. A content of 10% N-15 in the nutrient solution of the seedlings w as sufficient for marking the aphids.