A TECHNIQUE FOR TESTING VARIETAL SUSCEPTI BILITY TO THE MITE T-URTICAE - APPLICATION TO BEAN, CUCUMBER, TOMATO AND STRAWBERRY

Varietal resistance is a major element in the integrated control of sp ider mites; it is the least expensive and the easiest technique for pl ant protection. In this context, the purpose of this study was to deve lop a rapid and reliable technique for evaluating strain susceptibilit y to spider mites. In laboratory conditions (24 degrees C), >99% mite increase potential was already expressed on d 12 of the oviposition pe riod. The curve of cumulated fecundity, limited to 12 d, and particula rly the size of the F1 generation, constitute useful criteria for dete rmining susceptible and resistant varieties. After fitting a logistic function and comparing asymptotic confidence intervals, a statistical analysis could be performed. In this manner, 17 bean, 6 cucumber, 4 to mato and 6 strawberry varieties were tested. Significant differences a ppeared, and some strawberry varieties may even be considered as total ly 'resistant' to Tetranychus urticae.