THE LIFE-CYCLE OF IXODES-RUBICUNDUS (ACARI, IXODIDAE) AND ITS ADAPTATION TO A HOT, DRY ENVIRONMENT

The life cycle of Ixodes rubicundus, the Karoo paralysis tick. was stu died under field conditions in the south-western Orange Free State, So uth Africa, by placing freshly engorged ticks in small containers. The life cycle extends over 2 years. The two regulating phases in the lif e cycle, which undergo a morphogenetic diapause during the hot and dry summer months, are the egg and engorged nymph. Possible behavioural d iapause in adults which suppresses questing activity before the end of March, can also serve as a third regulating phase. Temperature affect s the duration of the pre-oviposition period of engorged females and t he period between detachment of engorged larvae from hosts and ecdysis . Commencement of larval hatch is reasonably synchronized. irrespectiv e of the month during which oviposition occurred. Peak activity period s of larvae (April or May) occur during a period of high rainfall and decreasing daily maximum temperatures. The period between detachment o f engorged nymphs from hosts and ecdysis is highly variable (8-36 week s). All developmental stages of the tick occur mainly during autumn an d winter and no ticks are active during the hot summer months of Decem ber to February. Larvae. nymphs and adults each survive for only one s eason.