Bacteria colonizing sentinel flowers in riparian and orchard habitats: do their volatiles attract beneficial insects?

Aphids are well-known secondary pests in many crops and entomologists seek biorational methods to prevent crop damage.  Recent studies have shown that honeydew from some aphid species harbor bacteria, yeasts and fungi, some of which produce volatiles that are attractive to beneficial insects.   The composition of aphid honeydew is mostly a complex of sugars and amino acids; similarly, high glucose floral nectar supports bacteria, yeast and fungi species.  This led us to ask if the same microbial species found in honeydews can be found in floral nectars. We conducted a survey of bacterial species that colonized sentinel flowers (Petunia sp. and Nicotiana sp.), placed in three riparian areas and three organic apple orchards in central Washington.  A total of 40 species from 16 genera of bacteria were identified by sequencing 16S rDNA.  Several species of bacteria identified from nectar have been found previously in aphid honeydew, while other bacteria appear to be unique to nectar. Using trapping studies in an organic apple orchard, we compared abundance of insects to bacterial colonies derived from nectar and those derived from honeydew.  In our first trial, one Bacillus sp. isolated from nectar attracted multiple Diptera.  We are completing analysis of three additional trapping studies in search of bacterial volatiles that are attractive to beneficial insects, which may support biological control in tree fruit orchards.