Stable carbon and nitrogen isotope signatures to determine predator dispersal between alfalfa and maize

• δ13C and δ15N analysis allow tracking predator movement between alfalfa and maize.
• Alfalfa is a source of C. septempunctata and O. majusculus towards maize in spring.
• Dispersal patterns differ between predators in summer.
• Maize acts as a source crop of O. majusculus towards alfalfa in summer.
• C. septempunctata does not disperse from maize to alfalfa.

The dispersal of Orius majusculus and Coccinella septempunctata between maize and alfalfa during the vegetative and reproductive maize growth periods was investigated, using carbon and nitrogen stable isotope analysis and aphids as herbivore prey at two locations of the NE Iberian Peninsula. The dispersal pattern of O. majusculus and C. septempunctata differs between these crops and also between different moments of the maize growth period. In the vegetative period the pattern was similar for the two predators and alfalfa acted as a source of predators towards maize. During the reproductive period, the dispersal of O. majusculus between the two crops was continuous but biased from maize to alfalfa, which mainly becomes a sink crop. All of the C. septempunctata collected on alfalfa were local and those collected on maize came from alfalfa, but there was no dispersal from maize to alfalfa. The present study increases knowledge of the dispersion of predators between arable crops and can improve habitat and landscape management at the farm scale by enhancing their biological control functions.

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