Species Complex and Temporal Associations between Coccinellids and Aphids in Alfalfa Stands in Spain

SIMPLE SUMMARY: Alfalfa is the main fodder crop of the irrigated crop systems of northern Spain, as well as many Mediterranean countries. Alfalfa crops are damaged by some pest species but are also considered to be vast reservoirs of natural enemies of these pests. However, in Europe, the relationships between these pests and their natural enemies have been poorly studied. The aim of this study was to fill this gap in the knowledge. Therefore, we characterized the coccinellid species complex, identifying sixteen species, and the numerical relationships of the two that were most prevalent—Coccinella septempunctata and Hippodamia variegata—with the different aphid species, which are considered one of the alfalfa pests. The numerical relationships were separately studied in each of the alfalfa growing periods between cuttings (intercuts). Whereas the abundance of C. septempunctata was correlated with that of A. pisum in the second alfalfa intercut, H. variegata was mainly correlated with the abundance of T. trifolii in the fourth intercut as well as with the overall aphid abundance in the fifth intercut. This study helps to increase the knowledge on the predator–prey relationships, which is crucial for the proper pest management of alfalfa and the agricultural ecosystems in which it is included. ABSTRACT: Alfalfa is known to be an important reservoir harboring natural enemies. The reduction in insecticide sprayings in recent years has allowed us to study the coccinellid species complex in this crop and the relationship between these predators and aphids. Alfalfa was sampled by sweep-netting throughout its productive period in several commercial stands each year between 2010 and 2021. The numbers and species of aphids and coccinellids were recorded. Sixteen coccinellid species were found. Coccinella septempunctata and Hippodamia variegata were, by far, the most prevalent species, with the former dominating during the first and second intercuts, whereas the latter dominated from the third to the fifth intercut. Acyrthosiphon pisum and Therioaphis trifolii were the most abundant aphid species, peaking in the second and fourth intercuts, respectively. Positive correlations were found between the abundance of C. septempunctata and A. pisum at the second intercut, between H. variegata and T. trifolii at the fourth intercut, and between H. variegata and the total number of aphids in the fifth intercut. This study helps to increase the knowledge on the predator–prey relationships of this crop and allows for designing strategies of conservation biological control against aphids.