Horizontal transmission of an obligate symbiont through conspecific frass

Microbial symbionts play a vital role in the health and function of their insect host. Obligate symbionts are commonly maternally transmitted with high fidelity. However, hosts may acquire their symbiont through more uncertain means. The arboreal leaf footed bug, Leptoglossus zonatus (Hemiptera: Coreidae), ingests its symbiont Burkholderia from the environment during the 2^nd instar. Transmission of Burkholderia is thought to require soil as a medium; potentially requiring a considerable journey from canopy to soil to locate the symbiont. We have shown that the symbiont can be acquired from leaf material when L. zonatus is abundant. This suggests transmission may be occurring from contaminated materials, even if at low rates. We asked whether L. zonatus can acquire Burkholderia from conspecific frass. We produced a cohort of L. zonatus infected with a Green Fluorescence Protein (GFP) labeled strain of Burkholderia. Frass was collected over 48 hours and presented to uninfected 2^nd instar nymphs in sterile petri dishes. Nymphs were reared to adulthood, their development time and adult mass recorded, and compared to nymphs without exposure to frass (negative control) and those fed the GFP Burkholderia in solution (positive control). Infection status was then examined using fluorescence microscopy to determine the presence of GFP Burkholderia. The results suggest that frass can serve as a vehicle for horizontal transmission of Burkholderia, but with variable efficiency. Nonetheless, the results suggest that frass from infected adults may play an important role in arboreal transmission of Burkholderia for L. zonatus.