Aceria fraxiniflora

Aceria fraxiniflora, the ash flower gall mite, is a species of gall mite that produces galls on ash trees. The male flowers of ash are greatly distorted by the mites, which results in a highly disfigured and disorganized gall that remains yellow or green, and later dries and turns brown. However, there is little evidence that this injury has a substantial impact on the ash plant's health.

Life history
Several generations of mites occur during the spring and summer season. During spring, female mites that have survived winter move toward developing male flowers to feed, which leads to the formation of galls. The eggs of the mites are deposited in the developing galls, and the nymphs that hatch out of these eggs live and feed inside the gall tissue. In fall, a generation of female mites develops, which overwinters in bark crevices under bud scales, after mating.

Biology
The adult female stage of ash flower gall mites survives the winter under protected areas such as bud scales on the ash tree. In the spring, with warmer temperatures, the overwintering females start feeding, begin forming galls, and lay their eggs on the newly expanding buds. This results in the development of small pouches in the flower tissue, where the mites continue to grow. As the galls dry up in mid-summer, the mites move to the bud scales for shelter during the following winter season.