After losing successful starter seedlings to crickets, I have had to undertake a total cricket eradication program in the greenhouse.
This included removing all dead leaves and debris from the floor, getting rid of clutter an extra buckets and other items that were not in use, and spraying the greenhouse floor, wall and doorway with an organic pesticide.
Essentria IC3 is an organic pesticide with plant oils as its active ingredients. Although I was skeptical that the product would work as I needed it to, it turns out that after two applications I have almost totally eliminated all crickets that were already in the greenhouse and ones that migrated into it after application.
I still must follow up with a light spraying daily in order to control the crickets that have entered each night through crevices and cracks between bricks in the floor of the greenhouse. But I have lost no more seedlings since I have using the product..