Abstract
The incidence of diapause at 15-20°C/9L15D was determined in 6 populations of the phytoseiid mite, Amblyseius womersleyi Schicha, collected from south-central and southern Japan. Diapause in phytoseiid mites is characterized by reproductive arrest in females, however, some females induced by short daylength and low temperature exhibited incomplete diapause as follows: 1)oviposition ceased after they laid a few eggs (“ switching” into diapause) ; and 2) the pre-oviposition period was much longer than that of females reared under a long-day photoperiod (“ reproductive delay” ) . In the populations from south-central Honshu and northern Kyushu, temperature greatly affected the diapause expression: almost 100% of the individuals entered diapause at 15° C and the percentages of diapause decreased with increasing temperature to 45-75% at 18°C and 10-40% at 20°C On the other hand, in the populations from Okinawa the percentages of diapause remained low (0-25%) over the temperature range tested, and temperature only slightly affected the expression of diapause. In particular, the percentage observed in the Tokashiki population was only 10.3%, even at 15° C. These results show that the diapause in A. womersleyi is a quantitative threshold trait and that variation in the diapause capacity exists within populations, as well as among populations from different localities. In some phytoseiid species, the importance of a thermoperiod for diapause induction has been shown, but in A. womersleyi a thermoperiod in combination with a short daylength (scotophase coincided with cool phase) held no stimulation for diapause induction.
