Inferring long‐distance movements of insects using combined hydrogen isotope and genetic analyses: A case study of the African edible bush‐cricket

Abstract The degree to which individuals within populations vary in whether, how far and what direction they disperse is central in order to understand many foundational questions in ecological entomology, including factors determining population and invasion dynamics, species' ability to respond to climate change or when designing conservation strategies for threatened species. This study combined stable hydrogen isotope analysis of nymphal and adult wing chitin with population genetic analysis of the cytochrome c oxidase subunit I (COI) gene to understand long‐distance movements of African edible bush cricket ( Ruspolia differens ) in East Africa. Results revealed that at most 77% of non‐swarming adults and 85% swarming adults originated locally, that is, within a range of a few hundred kilometres. In contrast, non‐local adults captured in Uganda likely originated from Ethiopia, Kenya or South Sudan based on the H isotopic evidence. Genetic analysis revealed 150 COI haplotypes with no significant differentiation among geographic source regions and no evidence of genetic isolation by movement distance. The observed frequent long‐distance movements, together with the historical records, which indicate that the swarm movements can be irregular in their direction, suggest that the movements represent nomadism rather than regular long‐distance migration. Our results thus provide a valuable case study of what characterizes nomadic movements in insects, which have been one of the outstanding open questions in movement ecology of animals.