Effect of photoperiod on the host-seeking activity and development of the larvae and nymphs of Ixodes nipponensis Kitaoka and Saito (Acari : Ixodidae)

Abstract

To examine the effect of the photoperiod on the host-seeking activity and development of I. nipponensis, the larvae and nymphs were exposed to three photoperiodic conditions (10L-14D, 12L-12D and 16L-8D) at 25℃. The host-seeking activity of unfed larvae was slightly suppressed by exposure to short-day photoperiods (10L-14D or 12L-12D) during the stages from eggs to unfed larvae. The host-seeking activity of unfed nymphs was strongly suppressed by exposure to short-day photoperiod during the stages from engorged larvae to unfed nymphs. The development of engorged larvae was little affected by the photoperiodic conditions before, during and after engorgement, although some of them entered diapause (lack of molting on 50 days after detachment) when they were reared at 10L-14D before, during and after engorgement. However, the developmental period of engorged nymphs was prolonged by exposure to short-day photoperiod. Diapause (lack of molting on 60 days after engorgement) occurred in engorged nymphs from the 10L or 12L groups reared at 10L-14D or 12L-12D during and after engorgement. Engorged nymphs from the 16L group did not enter diapause irrespective of the photoperiodic condition during and after engorgement. The diapause of unfed nymphs synchronizes nymphal activity with the favourable seasons of spring to summer. However, the diapause of the engorged nymphs has no effect on the activity of I. nipponensis because the nymphs disappear in the short days of autumn.