The locomotor activities on sites covered by silk produced by related and unrelated spider mites in Tetranychus urticae (Acari: Tetranychidae)

Abstract

The two-spotted spider mite Tetranychus urticae is a silk producer known to live in groups with a common silk web that can cover entire plants and protect mites against predators, rain and wind. Silk also plays an important role during collective migration by aerial dispersal or by walking. In this context, we studied the locomotor activity i.e. time in movement, in resting, and in static exploration (probing behaviour) of an individual confronted to clean places and/or places covered by silk coming from its own population or from another. Two populations were tested, one of the red form (Tunisia) and another of the green form (Belgium). The experimental results showed that the presence or the absence of silk did not influence the relative proportion of each behavioural item either for the red or the green population. Individuals of the green form population spent more time moving and less time resting than individuals of the red form population and this, whatever the substrate (red/green silk, clean). Moreover, the silk from the red form population attracted individuals from both populations, whereas the silk produced by the green form population did not attract any individual either from the red or the green form. This surprising result might have been due to a difference in the quantity and/or quality of silk woven by the two forms. We discuss how the differences observed in the behaviour of these two populations may result from differences in their strategy to rapidly increase the population of the colony and reinforce the silk nest.