Study on the Vectoring Potential of <i>Halyomorpha halys</i> for <i>Pantoea stewartii</i> subsp. <i>stewartii</i>, the Pathogen Causing Stewart’s Disease in Maize

Pantoea stewartii subsp. stewartii (Pss) is a Gram-negative bacterium native to the Americas and the causal agent of Stewart&#039;s disease in maize (Zea mays), which partic-ularly affects sweet corn. Although spread primarily by insect vectors such as the common corn flea beetle (Chaetocnema Pulicaria) in the United States, Pss has now been introduced globally, including regions in Africa, Asia, the Americas and Europe via the seed trade. Within the EU, it is a regulated quarantine pest. Although there have been detections in Italy since 2025, it is now considered eradicated. Surveillance and diagnostic efforts, supported by European and national projects such as Valitest, EURL-BAC and PROTEGGO, have focused on early detection and understanding of potential insect vectors. Recent studies in Italy have identified potential alternative vectors, including Phyllotreta spp. and the invasive Asian brown marmorated stink bug (Halyomorpha halys), the latter tested positive for Pss in PCR screenings, raising concerns due to its broad host range and global distribution. This information has prompted studies to verify the ability of Halyomorpha halys to vector Pss in order to assess the risk and prevent further spread of Pss in Europe. Studies have shown that in some cases the insect was able to take up the pathogen but was not able to transfer it to maize plants. Further studies should be conducted to verify whether other insects exist as potential vectors of Pss in Europe.