Summary
The workshop reviewed a number of aspects of cattle tick control including the incidence, avoidance and management of acaricide resistance. Currently there are only three classes of compounds that are effective against all strains of cattle tick, namely the macrocyclic lactones (MLs), fluazuron and the anti-tick vaccine Tickgard. A further two chemical classes, the amidines and synthetic pyrethroids, are also effective for cattle tick control in regions where the parasite has not developed resistance to the respective chemicals. However, single and multichemical resistant tick strains have evolved in some regions and emerging resistance to existing chemicals is likely to limit the lifespan of current chemical control measures.
Strategies to rapidly detect emerging resistance, or to predict its likelihood during the development of new chemicals, appear to be important to prolong the effectiveness of chemical controls. The use of MLs in the control of cattle ticks was reviewed, as was the use of the recently re-released TickGard vaccine. This vaccine is currently not widely used in the northern beef industry mainly due to the high frequency of treatments required. However the vaccine appears to have potential for wider use in tick control programs in conjunction with other control measures. Studies conducted at the time the vaccine was first launched, indicated that fewer treatments were necessary than is currently recommended, thereby increasing the attractiveness of this option. Pasture management strategies to control tick numbers in paddocks was reviewed and appears to offer potential for inclusion in future control recommendations, particularly in view of increasing chemical costs and tick resistance.
A balance must however be achieved between pasture management to reduce tick numbers and pasture management for optimum cattle productivity. A six-week spelling period appears to significantly reduce the numbers of tick larvae on pasture without affecting the quality of tropical pastures. Experiences from tick control programs in the Queensland dairy industry were presented and highlighted a range of issues associated with the communication, implementation and rate of adoption of such programs. The experiences and outcomes from the dairy program should be carefully considered by the beef industry prior to promotion of best practice cattle tick control programs to this sector of the industry. The key issue presented was the need for a simple and effective program that is easily communicated. The changing face of cattle tick regulation, particularly in Queensland, was discussed, as was the use of tick fever vaccines for the control of tick borne diseases.
Significantly, there is a move to privatisation of the delivery of services at clearance sites along the tick line and the use of tick control staff for a range of other activity including animal welfare functions. An imbalance exists where producers that benefit from the regulatory control of ticks (those in the tick free areas) do not necessarily pay for that benefit. The morning session of the workshop concluded with a presentation on current best practice recommendations for cattle tick control in beef cattle. A workshop session was held to review the combined use of pasture management, vaccination and chemicals to achieve sustainable tick control in endemic areas and to eradicate ticks on individual properties, with a view to reducing chemical usage and delaying the development of resistance to existing chemicals.
Control programs that exist for beef cattle are largely adequate at this time. The combination of resistant genotypes of cattle and the slower (apparently) emergence of resistance to acaricide on farms with beef cattle (compared to dairy) has resulted in a range of options still being available. These options are under some threat. There is a quoted trend in the reduction in the proportion of resistant (Bos indicus) genotypes due to market pressures. There is also continuing emergence of resistance by ticks to acaricide, most notably on some tick clearance sites in central Queensland. The rate at which these threats will be generally realised is uncertain. An important message was the need to identify and communicate the economic rationale for beef cattle producers to invest in voluntary tick control strategies, as the major driver in tick control is primarily the current regulatory requirements.
The afternoon session of the workshop turned the group's attention to the future of tick control over the next 25 years. Presentations were delivered on host resistance and other immunological approaches to tick control, biocontrol measures, pheromone-based control measures and the potential for the development of new pharmacological solutions. The development of gene markers for tick resistance in cattle received strong endorsement from industry, as did improvements in anti-tick vaccines. The hunt for these markers may prove elusive but was seen as a long-term sustainable way to manage ticks. The development of biological and pheromone control options also offer hope for the future.
Research is currently progressing on the use of a fungal pathogen for cattle tick control. Genomic information on ticks suggests that there are a large number of potential targets for new acaricide chemicals, however unlike nematodes and insects, molecular genetic tools and assays for tick target validation are still undeveloped due to the smaller market potential for acaracides. It was suggested that in the short term, new validated targets are more likely to come from basic research on tick toxins, biological pathways and mode of action work for new insecticidal compounds that also have acaricidal action.
