HOST-RESISTANCE TO CATTLE TICK (BOOPHILUS-MICROPLUS) IN BRAHMAN (BOS-INDICUS) CATTLE .4. AGES OF TICKS REJECTED

The stages of development of Boophilus microplus against which Brahman (Bos indicus) cattle manifest resistance were investigated by analysing the age distributions of ticks in populations on five steers showing different levels of resistance. The populations of ticks were established by infesting the steers each day with 1000 larvae, until each animal yielded a relatively stable number of engorged female ticks daily. The ticks were recovered by killing the steers and processing their hides in hot caustic soda. Ticks were allocated to age categories on the basis of their lengths. Analyses of the age distributions showed that between 36 and 80% of larvae were rejected in the first 24 h, and losses were greater from hosts with high levels of resistance. Some newly moulted nymphs failed to establish and were lost, and the growth of newly moulted females was retarded but most engorged successfully. The results also indicated that significant numbers of larvae and nymphs were lost either during the final stage of engorgement or after they had engorged. These findings are compared with losses of the tick from European (B. taurus) cattle. © 1979 CSIRO.