Temporal drop-off pattern of juvenile Ixodes pacificus (Acari: Ixodidae)

We determined the temporal drop-off pattern of juvenile western black-legged ticks, Ixodes pacificus Cooley and Kohls, by recording the time of day that replete ticks dropped off common laboratory-reared and field-caught rodents. The majority of subadult ticks dropped during daylight hours. Larvae that attached to nocturnally active murid or diurnal sciurid rodents left their hosts during slightly different periods of the day. Larvae primarily departed from murids between 14:00 and 18:00 and from sciurids between 10:00 and 14:00. Drop-off of nymphs from rodents was significantly greater between 14:00 and 18:00 than between 18:00 and 06:00, although nymphs tended to leave BALB/c white mice earlier in the day. Because subadult ticks leave diurnally or nocturnally active hosts at the same time of day, drop-off appears to be independent of the temporal patterns of host activity. Diurnal drop-off will result in engorged ticks remaining in the nests of nocturnal hosts but dropping to the ground from diurnal hosts. Thus, we propose that temporal patterns of host activity mediate the spatial distribution of I. pacificus.