Boophilus microplus: the effect of host resistance on larval attachments and growth.

Growth and behaviour of Boophilus microplus larvae on British breed cattle, with different resistance levels to the tick, were studied to elucidate the nature of resistance. On highly resistant animals, larval growth rate was slower for the first 3 days, but by day 4 they had attained the normal weight and the majority were subsequently able to moult. Using phosphorus-32 labelled larvae, it was found that attachment times were shorter and more time was spent wandering on highly resistant animals during the first 16 h. On the second day, attachments had stabilized, but more detachments were still made from highly resistant animals. This was considered to impose an additional stress as the cattle skin environment can rapidly desiccate larvae. However, the larvae were able to compensate by uptake of fluid from the host. Loss by repulsion of live larvae from the host or drowning in serous exudate were also not considered of major importance. The nature of rejection is discussed in a further paper. The distribution of larvae after 24 h suggests that their early behaviour largely determines the areas favoured by adults. Movement to, and accumulation in, favoured areas is discussed.