Dissemination of Bacteria Antagonistic to Erwinia amylovora by Honey Bees. S. V. Thomson, Professor, Department of Biology, Bee Biology and Systematics Laboratory, USDA-ARS, Utah State University, Logan 84322-5305. D. R. Hansen, K. M. Flint, and J. D. Vandenberg. Research Technicians, Department of Biology, and Research Entomologist, Bee Biology and Systematics Laboratory, USDA-ARS, Utah State University, Logan 84322-5305. Plant Dis. 76:1052-1056. Accepted for publication 27 May 1992. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1992. DOI: 10.1094/PD-76-1052.

Foraging honey bees (Apis mellifera) were tested for ability to disseminate bacteria antagonistic to Erwinia amylovora to apple and pear flowers in commercial orchards. The bacteria, Pseudomonas fluorescens and E. herbicola, previously known to provide biological control of fire blight, were placed on apple or cattail pollen at populations of 10⁹ and 10⁸ bacteria per gram, respectively. There was no significant decline in viable bacteria on either pollen over 3 wk at 4 C. These bacteria-treated pollens were placed in pollen inserts in the entrances of beehives. Honey bees emerging from these hives through bacteria-pollen mixtures acquired an average of 10⁵ and 10⁴ cfu per bee of P. fluorescens and E. herbicola, respectively. E. herbicola was detected on 92% of the apple flowers in a 2.6-ha orchard 2 days after the start of one study. In a pear orchard, 72% of the flowers within 7.6 m of the hive were colonized with P. fluorescens (average population of 10² cfu per flower) 8 days after the start of the study. Our study showed that bees can be efficient vectors of antagonistic bacteria for biological control of fire blight; disease control could not be evaluated because of frost and absence of disease in the test orchards.