On the perception of leaf morphology and visible light by Tetranychus urticae Koch (Acariformes, Tetranychidae)

The two-spotted spider mite Tetranychus urticae is one of the most polyphagous and most damaging pests worldwide. The behaviour of the mite differs on its various host plants and this could influence crop defence strategies. We investigated the perception of leaf morphology by T. urticae in relation to the effects of visible light on the selection of sites on which females prefer to live and feed. Mite females chose the shaded surface when smooth and glabrous lemon leaves were offered as a surface for living and feeding, showing a photophobic behaviour. However, they clearly preferred the abaxial surface of bean leaves regardless of the presence or absence of visible light. As no differences were found regarding the food quality between the adaxial and abaxial leaf surfaces, mite behaviour seems to be related firstly to the perception of leaf morphology and secondly to visible light. As regards the first factor, T. urticae prefers the abaxial surface of leaves with a complicated architecture, i.e. veins in relief, on which they can easily build their dense web, and this factor has priority in comparison to the negative effect of the visible radiations. The second factor is important on smooth and glabrous leaves, these being unsuitable for building the complicated characteristic webs of T. urticae.