Drop-off rhythms and survival of (Acari: Ixodidae) fed on crossbred (Friesians x Zebu) calves in Sudan.

is one of the most economically important ticks in the Sudan It is the main vector of tropical theileriosis in cattle and other diseases in different species. The study aims to investigate the drop-off rhythms and survival periods of tick stages fed on crossbred calves. Larvae, nymphs and adults fed on crossbred calves (male, 3-6 months old, Friesians x Zebu) kept under zero grazing system. Drop-off rhythms of engorged stages were studied under field conditions while the survival periods of unfed stages were investigated under field and laboratory conditions (27 °C and 85% R.H.). Significantly high numbers of engorged larvae dropped at night between 20H:00 and 07H:00. (March, April and August). Engorged nymphs dropped late evening and early night 16H:00-20H:00. (September), while insignificant number of engorged females dropped between 10H:00 and 14H:00 (October). Survival durations of unfed stages were longer under laboratory conditions than in the field. These were 99.36 ± 1.24 and 13.12 ± 0.68 days for larvae, 63 ± 1.33 and 16 ± 0.87 days for nymphs and 90 ± 3.6 and 45 ± 2.7 days for adults, respectively. Under field condition survival studies were conducted in May, August and December 2016 for larvae, March, May, August and December 2016 for nymphs and in October 2016 for Adults. In August, 70% of unfed larvae and nymphs survived for three weeks and 2.5 weeks, respectively, in May, 16% of unfed larvae survived for one week while no unfed nymphs survived for more than 4 days. This finding may indicate that larvae are more resistant to desiccation than nymphs. The abnormal changes on the alloscutum of desiccated nymphs and females were observed being shrunken and truncated posteriorly, a finding which opens new avenues for further studies. For control strategies more studies are recommended on the dropping to allow ticks drop in an area not suitable for further development as one of the control strategies and the survival studies also is exploited in rotational grazing of animals.