Genetic structure of a greenhouse population of the spider mite Tetranychus urticae:: spatio-temporal analysis with microsatellite markers

The genetic structure of a greenhouse population of the mite Tetranychus urticae was studied by the analysis of five microsatellite loci. Genetic variation was compared during a crop season between periods of population foundation and rapid population increase and was investigated in two consecutive years. The population displayed significant heterozygote deficiency at all the sampling periods. However, inbreeding tended to decrease with increasing density (F-IS coefficient between 0.13 and 0.25). No significant genetic differentiation between samples was found either at a spatial scale within the greenhouse or at a temporal scale between two growing seasons (F-ST between 0.008 and 0.09). Estimations of the genetic relatedness between pairs of individuals indicated that the distances between pairs of sisters and unrelated mites in the greenhouse were not significantly different, suggesting that mites do not tend to form patches that reside close to the point of birth.