Population genetics show that aphids (Hemiptera: Aphididae) are limited by summer host-plant distribution at the regional scale

Nasonovia ribisnigri (Mosley) is a severe aphid pest of outdoor lettuce, and the combination of sporadic and unpredictable colonisation on outdoor lettuce, along with the breakdown of cultivar resistance, has left few effective control methods. The population structure (spatially and temporally) of N. ribisnigri is currently unknown in England, and therefore microsatellite markers were designed to estimate the impacts of hostplant selection pressure (including host plant resistance) and environmental change. Biological samples collected between 2003-2020 from 10 sites across England were typed with microsatellite markers. The analysis of eight microsatellites indicated a clear East-West divide between N. ribisnigri populations which corresponds with current outdoor lettuce cultivation distribution in England, one of the aphid's summer hosts. Analysis of gene flow indicated that aphids did not leave the eastern region; instead, there was strong evidence for aphids migrating from the West into the secondary host eastern region, possibly from the winter host (Ribes spp.) in Spring. This result suggests that although N. ribisnigri has the potential for long-distance migration, strong ties to the summer host (lettuce) determine migratory behaviour at the population level. Nasonovia ribisnigri are mostly holocyclic and show a high level of inbreeding. Long-term trends revealed relatively stable populations, despite a recent breakdown of host plant resistance and other environmental changes, including favourable temperatures. The geographic and temporal structure of the N. ribisnigri population is discussed in relation to future pest management strategies.