Corn leaf aphid, Rhopalosiphum maidis Fitch (Hemiptera: Aphididae) endosymbiotic bacterial diversity along a gradient of maize management and climate conditions

A detailed field assessment and systematic sampling of corn-leaf aphids (R. maidis) were conducted annually over a five-year span from 2019 to 2023. The maize fields were selected considering two main aspects: the geographic locations and the maize cultivation systems which represents the whole European maize cultivation systems. In 2019, collections were made from two distinct types of agricultural environments. The first type encompassed traditionally managed (low-input) fields characterized by high agricultural and natural landscape diversity. These fields were situated in the Sighișoara area (Saxon region) of Central Transylvania, Romania. The second type consisted of high-input agricultural fields, which had been subject to chemical treatments and fertilizers, and were cultivated as monocultures with low natural landscape diversity. These high-input fields were located in Northern Romania and represented areas where intensive maize monoculture practices had been in place for over a decade. Between 2020-2021 a comprehensive sampling strategy was implemented for each management system, involving the selection of two maize fields per system, with two sample sites within each field. The large-scale monoculture fields were selected from western Romania (Banat region, Timis County), approximately 15 km apart. Medium-scale fields were situated in central Romania, in the vicinity of Sfântu Gheorghe city, characterized by semi-intensive maize monocultures spaced about 10 km apart. Small-scale maize fields were positioned in central Transylvania, near Târgu-Secuiesc city, with an inter-field distance of approximately 8 km. Additionally, local gardens were sampled in the Sighișoara area (Saxon region) of central Transylvania, Romania, with fields situated about 5 km apart.