Optimizing long-acting acaricide use for integrated tick management of Rhipicephalus australis-infesting cattle in New Caledonia.

The tick Rhipicephalus australis, formerly known as Rhipicephalus microplus, is the most economically important ectoparasite of livestock in New Caledonia, affecting cattle health and production. Decades of control attempts based on the application of chemical acaricides have exerted a strong selective pressure on R. australis populations, some of which have evolved resistance to these treatments. Research to develop integrated tick control programs is now focused on decreasing applications of chemicals. This study reports the implementation of a method of pasture and herd management involving minimal strategic use of long-acting acaricides, here defined as those having substantial efficacy against larvae for several weeks. Diverse parameters concerning the utilization of long-acting acaricides in association with pasture and herd management on 21 New Caledonian farms over a 5-year period were analyzed to optimize their strategic use. Longer larval acaricidal effect was achieved with a commercial pour-on formulation of fluazuron than with a commercial injectable (subcutaneous) formulation containing 3.15% ivermectin. Pasture and herd management allowed an increase in the delay between a long-lasting acaricide application and the subsequent acaricide treatment from 11.0 weeks to 17.7 weeks. However, if ticks were detected and reported by producers on the day of a long-acting acaricide application, the delay to the following treatment was reduced from 18.5 weeks to 11.2 weeks. The impact of a long-acting acaricide treatment on larval populations in pastures was greatest with a stocking rate of 5 animals per hectare grazing during 1 week. These results provide science-based evidence to cattle producers for adaptive integrated tick management in order to delay the development of acaricide resistance.

Development of a new approach of pasture management to control Rhipicephalus microplus infestation.

Despite several decades of chemical control, the cattle tick Rhipicephalus microplus remains an important constraint for cattle farmers. The regular use of chemicals has led to the development of tick strains that are multi-resistant to acaricides. New methods of tick control are being developed and combined in integrated tick management programs. Grazing management is one part of these control methods. However, until now, grazing management consisted essentially of resting pastures for 4 to 5 months. This amount of time is generally sufficient to allow for natural tick larvae mortality to occur, but this method often compromises the quality of forages, which is less than optimal at the time of arrival of the animals in the paddock. In this paper, we propose a new approach to pasture management-based tick control that optimizes forage production. It is based on tick development biological parameters, herd management and strategic treatments. This approach was tested for 2 years on two farms raising tick-susceptible European breeds of cattle under tropical conditions. The number of chemical treatments decreased respectively by 82.9% and 70.9%. This cost-effective approach may prove useful in decreasing the number of acaricidal treatments on farms facing high tick loads.