Intercrop movement of heteropteran predators between alfalfa and maize examined by stable isotope analysis

Alfalfa is a reservoir providing natural enemies to adjacent crops. However, whether these crops act only as receptors or also as donors is unknown. The pattern of movement between alfalfa and maize of Orius majusculus, Orius niger and Nabis provencalis and the role of both crops as “donor” or “receptor” were inferred through carbon and nitrogen stable isotope analysis. Results show that all heteropteran species are able to move between crops, but the predators’ movement is species specific and the role of alfalfa and maize as “donor” or “receptor” varies. The movement is also affected by crop management practices such as alfalfa cutting. All heteropterans that colonized maize at its early stage came from alfalfa, but N. provencalis also moved back to alfalfa from maize. Alfalfa cutting triggers movement of heteropterans to maize, but the time when this practice is performed also affects the movement. Alfalfa cutting did not have consequences on the recolonization of alfalfa, and some of the heteropterans found during the alfalfa regrowth period seem to have remained within alfalfa (mainly N. provencalis) while others came from maize (mainly O. majusculus and O. niger). When maize was harvested or dry, O. majusculus moved to alfalfa later than the other two predators. Due to the movement capacity of heteropterans between alfalfa and maize and the variable role of both crops as “donor” or “receptor”, conservation biological control could be enhanced by including adjacent fields of alfalfa and maize or a mosaic of both crops at farm and landscape levels.