You would expect acaricide treatment of animals to be least effective against which tick?

• A. Rhipicephalus appendiculatus
• B. Ornithodoros erraticus
• C. Amblyomma variegatum
• D. Boophilus annulatus

Answer: (B)

Acaricide effectiveness on ticks depends on how the tick lives and feeds. Hard ticks (the ones that stay attached on the host for long periods while feeding) are more likely to be killed by topical or systemic treatments because they’re exposed to the chemical for an extended time during feeding. Soft ticks, like Ornithodoros erraticus, behave differently: they are nidicolous, often living in cracks, bedding, or animal housing, and they feed very quickly—within minutes—then drop off. Because they spend little time on the host and spend much of their life off the animal, the acaricide applied to the animal has less opportunity to contact and kill them. The other ticks listed are hard ticks, which are typically more susceptible to standard acaricidal treatments on animals, making Ornithodoros erraticus the least effectively controlled by those treatments.