Genetic structure of a phytophagous mite species affected by crop practices: the case of Tetranychus urticae in clementine mandarins.

Tetranychus urticae Koch is a cosmopolitan mite considered as the most polyphagous species among spider mites. This mite is a key pest of clementine mandarins in Eastern Spain, where Spanish clementine production concentrates. Crop management practices can affect the population dynamics of this mite and, consequently, its impact on the orchard. Microsatellite markers were used to study mite population genetics from two commercial orchards which had been managed differently following Integrated Pest Management (IPM) or Organic Pest Management (OPM) schemes during four consecutive years. A multiplex system including 20 microsatellite loci was designed specifically and allowed an efficient and inexpensive genotyping of individual mites. We found that the IPM population had a stronger fluctuation of population structure and higher genetic diversity compared to OPM population. Thus, our study concludes that crop management has an impact on the population genetics of T. urticae which may be related to the alternation of some acaricides under IPM.