EFFECTS OF PHOTOPERIOD, TEMPERATURE, FOOD AND RELATIVE-HUMIDITY ON THE INDUCTION OF DIAPAUSE IN THE PREDATORY MITE AMBLYSEIUS-POTENTILLAE

Aspects of the induction of diapause were studied in a Dutch strain of the phytoseiid mite Amblyseius potentillae. The photoperiodic response curve was of the long-day type, with a sharply defined critical daylength of 14.5 h. Critical daylength varied only little at temperatures between 15.0 and 22.5-degrees-C. All post-embryonic and possibly even late-embryonic stages of development were found to be sensitive to photoperiod; sensitivity appeared to be maximal during the protonymphal stage. It is shown that beta-carotene is necessary for some early step in the physiological mechanism of photoperiodic induction, and not (or not exclusively) for the expression of the diapause response. Two points of sensitivity to light could be demonstrated in the nights of L:D 13:11 and L:D 12:12 long-night regimes, using 1-h night interruptions. These results are similar to those obtained in light-break experiments with spider mites and insects. However, no effect was found with light interruptions appeared during the dark phase of an L:D 10:14 long-night regime. In resonance experiments with a constant photophase (12 h) and a variable scotophase, a weak rhythmic response was found at 22.5-degrees-C; at 19.0-degrees-C this effect was completely absent. The relative humidity experienced by the mites during diapause induction as well as during diapause development influenced the rate of diapause completion under long days (L:D 16:8). Diapause duration appeared to be shortest when the mites experienced low relative humidity (35 +/- 5%) during diapause induction and high relative humidity (75 +/- 5%) during diapause termination, and longest under the reverse conditions.