Isotopic marking of natural enemies fed on C4 honey for habitat management studies in agroecosystems

Abstract

Abstract 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 C4 (sugar‐cane) or C3 (muti‐flower honey) diet could help mark and track predators that feed on them. 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. δ13C and δ15N values from wild individuals helped distinguish them from marked ones and determine the habitat resources they used. Green lacewings fed on C4 showed significantly higher δ13C 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 δ15N values for both wild populations indicated both predators had similar prey, but different vegetal resources (different δ13C values). Sugar‐cane honey is a natural and reliable marker for tracking lacewing populations in the field, but not for parasitoids.