Fig. 1.

Scaptomyza flava larvae can spread plant-colonizing bacteria within leaves. A) A S. flava larva deposits frass ([2] small white circle) upon leaving the feeding site in the B. vulgaris leaf ([1 and 2] large white circles). After having fed elsewhere in the leaf, the larva later returns to continue feeding at this site ([3] overlapping large and small white circles). B) S. flava larvae can spread plant-colonizing bacteria within leaves through the behavior described in (A). Bacteria attached to the larval cuticle can be deposited on other host plants, as shown here where a S. flava larva that fed on a leaf of a Psm ES4326 cfa6-infected B. vulgaris source plant was allowed to crawl on a selective King’s B agar plate. C) Cuticle wash from a larva that had fed on a Psm ES4326 cfa6-infected leaf spread on a selective King’s B agar plate. D) Mean accumulation of Psm ES4326 cfa6 after pre-inoculation of B. vulgaris source leaves prior to and after two days of larval feeding, and accumulation of Psm ES4326 cfa6 in recipient leaves on which larvae from infected source leaves were feeding. Error bars represent standard error of the mean. Asterisks indicate statistically significant differences in bacterial accumulation in pair-wise comparisons (two-tailed Student’s t-test, P < 0.05). Scale bars in (A) and (B) indicate 2 cm; (C) is depicted at the same scale as (B). Photo credit: Matthew Velazquez (A).