Hi Bob –
Trichogramma are shipped as pupae in host eggs, glued to paper strips, and arrive ready to hatch out as adult wasps. Releases should be made when moths are first present and periodically thereafter. Use 5,000 parasites (1 square) per 5,000 square feet weekly, or every other week for 3 to 6 consecutive weeks.
Rain will not hurt the young parasites, but cooler weather will delay their hatch. Ants can be a problem as they eat the eggs. However, placing them in strategic areas should prevent this.
Tip: Hang each square from a piece of thread, and fasten the cup they arrive in over the eggs (like a bell). This will protect the moth egg parasites from ants and help keep them dry.
Good luck!