Ticks

Ticks prefer warmer parts of New Zealand and are found mainly on the east coast of the North Island, Waikato, Manawatu, Wairarapa and Nelson. With warmer temperatures ticks have been found on deer and cattle in Otago and Southland more recently. However it is not known whether tick numbers will thrive and multiply in these cooler districts.

Ticks move on and off hosts three times within their life cycle. Each of these stages can be on a different animal species. Adult ticks lay about 1000 eggs on the soil in mid-summer. They hatch to larvae late summer-early autumn. Larvae move up pasture and attach to a passing host upon which they engorge lymph and blood. At this stage they about 1-2mm. After three to five days they drop from the host and return to pasture where they moult to become a nymph. This nymph can over-winter in quite cold temperatures. In spring the nymphs (now 2-3mm) attach to another host and engorge again (over three to five days), expanding to about 5mm. They drop off, moult to become adults. The early mid-summer than attach to a host again and engorge to about 10mm (over three to five days). They then drop off to lay eggs, completing the life cycle.

Figure A: Life cycle of the NZ Cattle Tick

Ticks affect deer by removing blood (around 0.75-1ml/tick). This can weaken fawns in particular, making them anaemic and bringing about death through blood loss. Up to 160 adult ticks have been found on ears of a new-born calf. If infestations are severe, deaths of new-born fawns are often the first sign. This is because ticks are difficult to spot until they are at the adult stage on a host (about the size of a small grape). Adult tick infestations typically coincide with fawning, a time when farmers are reluctant to yard deer for close examination.

As well as calf deaths, ticks can cause scarring on hides and velvet, downgrading their value. They also predispose deer to parapoxvirus. Small numbers will not affect the animal.

They are easily confirmed visually at the adult stage. To gauge which paddocks are most heavily affected drag a towel over a number of different blocks when ticks are active and count the numbers attached.

Tick control is very challenging and eradication is impossible. Timing control measures to fit with deer management can be difficult i.e. treating newborn calves. If only small numbers are present and the farms environment is challenging for tick survival then it is likely that no action is needed. If ticks are widespread then control methods should be considered. They include:

• Spray or pour-on for deer (a 1% flumethrin solution is effective for up to three weeks).
• Ear tags impregnated with medication toxic to ticks.
• Reducing tick survival on pasture through cultivation (target paddocks with reeds or long grass and scrub as they provide the best home for ticks).
• Spelling pasture for 12 months to break tick cycle (not effective if wild mammal pests present).
• Introduce ‘taxi’ stock like sheep or cattle to pick up ticks off the pasture, and then kill ticks with spray or pour-on treatment.
• Spraying paddocks with insecticide is not recommended as it only kills ticks on the pasture at that time and can have a negative effect on other beneficial insects like bees.