Biocontrol potential of Pseudomonas and Pantoea strains against the lettuce root aphid ( Pemphigus bursarius L.) in witloof chicory ( Cichorium intybus L. var. foliosum )

Abstract BACKGROUND Although microbial biopesticides are widely applied to manage foliar insect pests, their application against belowground insect pests has received less attention. These pests are generally more challenging to manage due to their concealed soil‐dwelling lifestyle and the limited availability of delivery methods. Here, we evaluated the potential of Pseudomonas and Pantoea strains as a biocontrol strategy against the lettuce root aphid ( Pemphigus bursarius ) in witloof chicory ( Cichorium intybus L. var. foliosum ) using a realistic delivery approach based on seed inoculation, preceded by a screening via root immersion to identify the most promising strains. RESULTS Root immersion of witloof chicory plants in bacterial suspensions significantly decreased aphid survival for 10 out of 19 tested strains, with median lethal times ( LT 50 ) ranging from 0.6 to 7.5 days, compared to 10.7 days for the untreated control. When the four best‐performing strains, including two Pseudomonas and two Pantoea strains, and a reference strain ( Pseudomonas fluorescens PpR24 ) were applied via seed inoculation, the strains successfully colonized chicory roots at densities exceeding 10 6 colony‐forming unit ( CFU ) g −1 of root tissue for at least 5 weeks and retained aphicidal activity, albeit with reduced efficacy. In addition, the strains significantly suppressed aphid population development, reducing total aphid population size by up to 82% at 21 days after aphid introduction. CONCLUSION In this study, we have identified novel Pseudomonas and Pantoea strains that effectively reduce survival and population development of Pemphigus bursarius on witloof chicory plants, highlighting their potential as a sustainable biocontrol strategy against root aphids. © 2026 Society of Chemical Industry.