Dietary range varies among Aphis craccivora populations associated with different host plants: Insights into the alfalfa–cowpea aphid system in Spain

Agroecosystems are frequently disrupted by aggressive management practices. In the case of alfalfa, regular cutting events during the season cause abrupt resource depletion, often leading to the spillover of insects into nearby areas. In this study, we assessed whether alfalfa populations of the polyphagous aphid Aphis craccivora Koch (Hemiptera: Aphididae) can utilize black locust and vetch, two common plants found near alfalfa fields, as alternative hosts following cutting events. We also determined the ability of these plants to act as A. craccivora reservoirs for the recolonization of alfalfa stands once regrowth occurs. To address these questions, we conducted host specialization trials involving host shifting in three different A. craccivora populations collected from alfalfa, black locust, and vetch. We recorded a comprehensive set of life history parameters using the two-sex life table procedure. The degree of host specialization varied among different A. craccivora populations. The alfalfa-origin population showed relatively good performance when shifted to either black locust or vetch, suggesting these plants may act as refuges for population rebuilding after cutting events, until alfalfa regrowth allows for recolonization. In contrast, populations originating from black locust or vetch performed very poorly on alfalfa, suggesting the colonization of alfalfa fields by these populations is unlikely. The mechanisms underlying host specialization in different A. craccivora populations and the observed differences in dietary diversity are discussed. This study provides valuable insights into the ecology of this insect in the most significant Spanish alfalfa-producing region.