Oviposition by the vagrant eriophyoid mite Aculops allotrichus on leaves of black locust tree, Robinia pseudoacacia.

Leaf-dwelling mites often prefer to feed on young leaves and also are more likely to inhabit the abaxial leaf side. The aim of our study was to examine whether leaf age may affect production and distribution of eggs on black locust leaves by females of Aculops allotrichus. The eriophyoids were tested for 2.5 days on 'trimmed' compound leaves (with only two opposite leaflets left), which were maintained in vials filled with water. For the experiments we used leaves of three categories: (1) the 'youngest', in which both halves of the adaxial side of leaflets still adhered to each other (and usually remained folded for the next few hours), (2) 'young' with already unfolded leaflets, and (3) 'mature' with fully expanded leaflets. The tested females laid significantly more eggs on developing leaves than on 'mature' ones, although they deposited the highest number of eggs on the 'young' leaves. The distribution of eggs on adaxial or abaxial leaf sides also depended on leaf age. On the 'youngest' leaves, eriophyoids placed similar numbers of eggs on both sides of a blade. However, the older the leaf, the more willingly females deposited eggs on the abaxial side. Our biochemical and morphometrical analyses of black locust leaves indicated significant changes in the contents of nutrients and phenols within leaf tissue, and in the density of trichomes and thickness of the outer epidermal cell walls, correlated with leaf age. Their possible effects on the production and distribution of eggs on leaves by A. allotrichus are discussed.