Impact of starvation on the silk attractiveness in a weaving mite, Tetranychus urticae (Acari: Tetranychidae)

The two-spotted spider mite Tetranychus urticae is a silk producer known to live in groups. Its silk production plays an important role in protection against external aggressions (predators, rains, etc.). It is also used for group dispersal through the formation of silkballs or as a thread during individual migration by walking. Until now, the role of silk in enhancing migration has been poorly studied. In this paper, the influence of the silken thread presence on T. urticae's locomotor activity is studied. One virgin female is placed at the centre of a cover glass partially covered by silk. Moving and resting time are studied on the silk or the clean part of the cover glass as a function of the starvation level of mites (fed vs. starved) and the age of the silk (30 vs. 60 vs. 90 vs. 120 vs. 150 min). Results show that a fed female spends more time on the silk-covered part than on the clean part as long as the silk is fresh (less than 120 min). Thus, the age-related changes in chemical and/or physical properties of the silk influence the spatial distribution of fed mites. Whatever the age of the silk, starved mites spend more time on the clean part of the set-up. Indeed, the silk freshly laid by conspecifics is attractive only for fed mites; starved mites probably prefer sites without silk (and conspecifics). This study shows that that the silk influences the spatial distribution of T. urticae according to its level of starvation and that silk is probably is an indicator of the presence of conspecifics.