Ticks follow fellows to tastiest cows.

Ticks follow fellow to tastiest cows

The southern African bont tick, which produces a deadly malady in cattle known as heartwater disease, prefers animals tested out by its peers, according to a study conducted in Zimbabwe and reported in the Jan. 20 SCIENCE.

The tick's discriminatory practice may aid the spread of heartwater disease, allowing ticks to steer clear of cattle treated with tick-killing agents in places where other animal hosts abound. It may also cause some unexposed cows to lose their immunity to the disease, report Conrad E. Yunker and Howard R. Andrew of the University of Florida in Gainesville and Zimbabwe government scientist Andy Norval.

Bont ticks apparently are drawn to their hosts by a chemical signal of approval left by their male tick predecessors. To test whether this results in choosy behavior, the researchers released 200 fluorescently tagged, male-female tick pairs downwind from two pairs of steers. One pair had already been infested with signal-emitting male ticks. Ticks downwind from the clean cows dispersed, but the tick-harboring cows served as a magnet for both marked and wild ticks. Another experiment confirmed that the tick-emitted chemical alone would do the trick, the scientists report.