Isotopic marking of natural enemies fed on C-4 honey for habitat management studies in agroecosystems

1. To improve biological control and habitat management, how pest predators spread from natural habitats to crops must be understood. We studied whether intrinsic differences in stable-isotopic ratios of C and N from an artificial C-4 (sugar-cane) or C-3 (muti-flower honey) diet could help mark and track predators that feed on them. 2. Two aphid predators solely feeding on sugar resources as adults were used: the green lacewing Chrysoperla carnea s.l., and the parasitic wasp Aphidius colemani. delta C-13 and delta 1(5)N values from wild individuals helped distinguish them from marked ones and determine the habitat resources they used. 3. Green lacewings fed on C-4 showed significantly higher delta C-13 values than those on C3 and wild individuals. However, parasitoid values were unaffected, with no mark acquired. Logistic regression was fitted to assess the probability of green lacewings having either diet with a probability of 0.93. Marks were acquired after 5 days and were detectable 20 days after switching diets with a probability of 0.67. Similar delta N-15 values for both wild populations indicated both predators had similar prey, but different vegetal resources (different delta C-13 values). 4. Sugar-cane honey is a natural and reliable marker for tracking lacewing populations in the field, but not for parasitoids.