Plant Parasites of Europe

leafminers, galls and fungi

Why are gall-mite galls so problematic?

The identification of galls that are induced by gall mines often leads to an unsatisfactory result. Sometimes the descriptions are partly incorrect, or overlapping, the nomenclature my be confusing and incongruous with other publications.

The causers of these galls measure 0.2 mm or less, are hardly visible with the naked eye. Identification is possible only by means of high power microscopes and carefully made preparations. Identification of a gall therefore boils down to the identification of a symptom: confirmation of the identification at the inducer is effectively impossible.

An additional difficulty is that the reaction of the plant is dependent on the size of the mite population. The same species of mite may be asymptomatic in one situation, may cause local silvering of a leaf in another, and at high densities may cause necrotic spots, and even curling of the leaves.

The galls of many of the most common European plants (Acer, Alnus, Betula, Prunus, Salix….) have been studied, and their causers named, around 1900, or earlier. After that period a long-time stagnation followed. All modern literature about the galls consists of a repetition and interpretation of what was seen, or better, could be seen, more than a century ago. The waiting is for an acarologist who is willing to repair this situation.