Although the mite probably exists at some level in most soil environments, it is believed that economic damage occurs when some disruption, such as reduction of natural enemies, or a sudden infusion of organic matter in the form of green mulch allows the resident population to increase to damaging levels. Research efforts are presently structured to monitor damaging levels of mites and to clarify the factors that cause these increases to occur. Nearly all garden vegetable plants, some forage and grain crops, and many weeds serve as hosts. Damage to plants results from the destruction of epidermal tissue and removal of cell sap from individual mesophyll cells. Feeding by nymphs is generally concentrated on young tissue between the leaf sheaths and the stem, but extensive feeding by adults on more mature tissue is not unusual.
Affected leaves display whitish or chlorotic blotches, as if they have been sandblasted.
If feeding is severe, particularly under drought conditions, the tips of leaves become brown. Prolonged feeding by infestations of thrips may eventually kill seedlings, reduce bulb size by decreased photosynthesis and increase the incidence of leaf and bulb rots. In some instances, perhaps because the overwintering host crop has been harvested, mass immigrations into onion fields have occurred over very short time periods. Eggs are laid in onion leaves and hatch in four to 10 days, depending on temperatures. Males are wingless and scarce, and females regularly reproduce without mating - allowing for the rapid increase of populations when conditions are favorable.