The dispersal and establishment of pseudomonad populations in the phyllosphere of sugar beet by phytophagous caterpillars

The role of phytophagous insects in the dispersal of phyllosphere bacterial populations has been investigated. Following seed inoculation, a leaf colonising population of Pseudomonas fluorescens SBW25EeZY6KX (lacZY and aph-xylE) was established in field grown sugar beet (Beta vulgaris var. amethyst). Third instar, Mamestra brassicae (Lepidoptera: Noctuidae) larvae were placed onto the emerging leaves of mature plants and the dispersal of the marked strain (ca. 5×105 cfu/g leaf) to untreated plants monitored. Forty-two days after caterpillar introduction, approximately twenty days after pupation of the larvae, an established population of transferred bacteria was detected at densities similar to those determined for seed inoculated plants of the same age. Under appropriate conditions phylloplane colonising pseudomonads can be dispersed by invertebrates and establish viable populations on the leaves of recipient plants.