We deployed six sticky traps in the onion patch immediately after planting in late April and replaced the cards in mid-June. The first set of cards collected a considerable number of what resemble, to my untrained eye, onion maggot flies and the onion plants remain healthy:
Each image shows both sides of a single card.
The cards sit a foot above the shredded leaf mulch and I managed to drop at least one of the cards while extracting it from the cage, but they all have plenty of onion maggot flies in addition to the random debris.
The cards inside their cages have not accumulated larger insects like honeybees / moths / butterflies, although the tiniest specks are definitely mini-critters along the beetle / gnat / aphid / mosquito axis.
Unlike last year, the second set of cards will remain in place until harvest to maintain continuous pressure on the fly population.
If you’re really interested, the dozen original camera images have more detail.