Eriophyoid mites are excellent candidates for ethological research using the approaches of behavioural ecology and sociobiology. These tiny haplodiploid mites are highly specialized plant parasites, producing galls, forming nests, inhabiting refuges or living freely on plants. They reproduce via spermatophores deposited on a substrate and without pairing, which is a fascinating, though still poorly understood, mode of reproduction widespread in some groups of arthropods. Eriophyoid males can be involved in external sperm competition. In some species they also guard pre-emergent females and deposit spermatophores beside them. Although slow-walking, the minute eriophyoid mites can disperse for long distances on air currents or specific animal carriers. After landing on a plant they can distinguish between suitable and unsuitable hosts. Biological observations on a deuterogynous species indicate that parasociality could occur among eriophyoid mites. Many eriophyoids are of economic importance. Knowledge of their behaviour may promote understanding their ecology, may resolve problems in their phylogeny and may help developing methods for their control. In this paper, attention is directed to dispersal modes of eriophyoid mites, their feeding and host acceptance, spermatophore deposition and mating, defence against predators, and social behaviour.

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Sex dissociation means that males deposit spermatophores regardless of the presence of females, while females independently seek spermatophores and pick up a sperm. In this study I describe unique behaviour of insects and mites that practice sex dissociation guarding of pre-emergent females (so called quiescent female nymphs). In particular, behaviour which is exhibited by Vasates robiniae males. When competitors were absent in the vicinity of quiescent female nymphs, guarders deposited ca 0.8 spermatophores per hour and placed them around their mates in a manner in which two subsequent spermatophores were situated more frequently within a relatively long distance from each other rather than close to each other. Between the acts of depositions males alternately explored the closest surroundings of the nymphs, at the rate of ca 7.4 times per hour, and became motionless, mostly in bodily contact with the nymphs. Interestingly, while some males guarded until the quiescent female nymphs started moulting, others left their mates at different times before moulting. Prior to departures, males markedly changed their behaviour, more frequently exploring and resting without bodily contact with the nymphs and tended to shorten the time of depositions as well. However, if males stayed with the mates until moulting, the forthcoming time of females emergence did not influence either spermatophore deposition, exploration or the motionless phase of guarding. During and after moulting, guarders also did not persuade or coerce females into picking up a sperm from their spermatophores.

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