ACCEPTABILITY OF STYLOSANTHES SCABRA VOGEL AS A SUBSTRATE FOR LARVAE OF BOOPHILUS MICROPLUS (CANESTRINI) (ACARINA: IXODIDAE)

Larvae of the cattle tick, Boophilus microplus ascend pasture in order to transfer to a passing host. Larvae ascending stems of several species of the genus Stylosanthes are immobilised and killed by the sticky secretion produced by these plants. If these plants are to be effective as control agents for cattle tick, larvae must find them as acceptable as the alternative vegetation. A technique to compare the acceptability of stems of different pasture species to tick larvae is described. The acceptability of buffel grass ( Cenchrus ciliaris ) was compared with that of Stylosanthes scabra cv Fitzroy grown in a glasshouse for 1 month or in the field for 7 and for 18 months. The acceptability of straws coated with sticky S. scabra exudate, and of sticks of different colours or thicknesses was also investigated. Compared with buffel grass, young stems of S. scabra or those grown in the glasshouse were less acceptable to larvae but thicker woody, 18 month old stems were more acceptable. The results suggest that larvae are unlikely to avoid mature Stylosanthes plants in the field. The sticky exudate from young S. scabra stems resulted in far fewer larvae coming to rest on coated straws. The colour of sticks did not influence the response of larvae but thicker sticks were more likely to be contacted than thin sticks. The implications of these results for the use of S. scabra as a tick control agent are discussed.