The larval stages of the daylily leafminer create silver tunnels as they feed in Hemerocallis leaves. The pale maggots may change direction as they feed, producing crossing or zigzagging tracks. Heavy mining has an aesthetic impact but the injury does not seem to kill plants.
The insect was discovered in Maine in 2008. By 2012 infestations were reported in Alabama, Florida, Georgia, Louisiana, Maine, Maryland, Mississippi, North Carolina, New York, South Carolina, Pennsylvania, Tennessee, Texas, Virginia and West Virginia. The leafminer was first noticed in Kentucky in 2013. Spread probably is facilitated by movement of infested plants.
Female flies deposit their eggs in leaves, often near leaf tips. Mature larvae pupate at the end of their mines. There may be three generations each year in Kentucky.
No control recommendations have been developed so removal of mined leaves before flies have emerged currently is the best option.
Information source: https://www.eppo.int/QUARANTINE/Alert_List/insects/ophiomyia_kwansonis.htm
By Lee Townsend, Extension Entomologist