EFFECTS OF SHORT EXPOSURE PERIODS TO LOW-TEMPERATURES ON THE BIOLOGY OF TETRANYCHUS-URTICAE

All stages of Tetranychus urticae Koch (Acari: Tetranychidae) were sub jected to short periods (0-16 hours) of exposure to low temperatures ( 0, -5 and -10 degrees C), followed by rearing at 20 degrees C. Adult s urvivorship was greater than that of the juvenile stages, but there wa s no difference between survival rates of the two sexes; duration of e xposure had more effect than the actual temperature experienced. Many surviving juvenile mites did not successfully complete their developme nt to adult: 8 hours at 0 degrees C was sufficient to prevent almost a ll development. The longevity of surviving treated adults was reduced, but there was little reduction in the adult longevity of surviving tr eated juvenile stages. Both duration and level of low temperature expo sure affected the fecundity of treated adults. Treatment at the deuton ymph stage-also affected the fecundity of the resulting adults. Male f ertility was unaffected by low temperature exposure, except possibly a t the longest exposure durations. Development of the surviving treated immature stages was retarded; the temperature experienced had more ef fect than the duration of exposure.