Role of contact pheromones on male mate preference for heterospecies in the two congeneric pest spider mites

Abstract: The tomato red spider mite, Tetranychus evansi and the two-spotted spider mite,Tetranychus urticae are important pests of tomato plants in Europe. Previous studies showedthat these two species co-occur on the common host plants and interact indirectly by theinduction and manipulation of host plant defences. They interact directly also, and wepreviously described that males of T. evansi showed a mate preference for T. urticae females,and that T. evansi colonies outcompete T. urticae colonies on plants where both species cooccurby reproductive interference. In the present work, we study the mechanism of male matepreference for heterospecies in T. evansi. We extracted pheromones of T. evansi and T. urticaefemales and compared the responses of T. evansi and T. urticae males and females to theextracts. By using a glass slide bioassay, we measured how long the extracts arrest an individualmite. We found that T. urticae males were arrested by the extracts from both species when theconcentration was low, and they were arrested only by the extracts from T. urticae femaleswhen the concentration was high. On the other hand, T. evansi males were not arrested whenthe concentration was low, and they were arrested by the extracts from both species when theconcentration was high. T. urticae and T. evansi females were arrested by the extracts fromconspecies when the concentration was low, however the effects disappeared when theconcentration was high. Differences in the pheromones between the two species females maynot work as the mechanism of male mate preference for heterospecies in T. evansi, but as themechanism of mis-mating in T. evansi males.