THE INFLUENCE OF PHYSIOLOGICAL AGE OF ARGAS-REFLEXUS LARVAE (ACARI, ARGASIDAE) AND OF TEMPERATURE AND PHOTOPERIOD ON INDUCTION AND DURATIONOF DIAPAUSE

The occurrence of diapause and quiescence was investigated in Argas re flexus engorged larvae, nymphs I and nymphs II. For diapause experimen ts, larvae were maintained at five different locations: at constant 20 degrees C long day (LD; 17 h light:7 h dark) or short day (SD; 10 h l ight:14 h dark), at two locations with natural photoperiod and tempera ture and at one location with natural photoperiod but constant 15 degr ees C. At 20 degrees C, diapause incidence was low in physiologically young larvae, increased with larval age, and then decreased to zero in specimens of increased physiological age. This pattern, observed both at constant LD and SD, suggests that the propensity to diapause chang es with the physiological age of the unfed larva. The duration of diap ause decreased with increasing larval physiological age at all locatio ns, resulting in a seasonally synchronized moulting pattern. The resul ts suggest that A. reflexus larvae are photoperiodically sensitive bot h before and after feeding and that decreasing daylengths may be parti cularly strong inductive stimuli. The developmental zero and thermal c onstant of the larvae were determined as 13.24 degrees C and 220 degre e-days, respectively. Degree-day measurements revealed that larval A. reflexus may enter a diapause of different length when fed between Aug ust and December and kept at natural daylength. Development of engorge d nymphs I and nymphs II, but not of larvae, was ultimatively restrict ed at a temperature of 37.5 degrees C, but immediately resumed at 25 d egrees C, demonstrating the occurrence of quiescence at high temperatu res. Similarly, at a low temperature of 15 degrees C, many nymphs I an d II did not develop within 58 months, but did so successfully after t ransfer to 25 degrees C, without additional food intake.