The Tropical Bont Tick (TBT) (Amblyomma variegatum), a parasite of both domestic animals and wildlife, was first introduced in the Caribbean in 1830, when infested cattle were imported into Guadeloupe from West Africa. It subsequently spread to the other Caribbean islands. The tick is associated with an acute skin disease, Dermatophilosis, and Heartwater, which can be lethal for ruminants.
An increase in the movement of livestock, both legal and illegal, between the Caribbean islands has played a part in the spread of the tick, but there is increasing evidence that migratory birds, especially the cattle egret, which carry TBT larvae and nymphs, spread the parasite. In this context, it is important to note that over the last 20 years, TBT has been spreading to new areas and islands, causing the loss of large numbers of animals because of its association with dermatophilosis, Thus, in Nevis, cattle numbers were reduced from 5 000 to 500 head in less than a decade.
The tick was found in 14 islands (9 members of the Caribbean Community and Common Market (CARICOM) and 5 French Territory). TBT poses a considerable threat to the livestock owners among IFAD target groups in the region, which include smallholder owners of cattle, sheep and goats. If the tick is allowed to reach the mainland countries America – South, Central and North – and become established, eradication of the tick and its associated diseases from the hemisphere would be impossible. In 1994, a regional programme, the Caribbean Amblyomma Programme (CAP) for the eradication of TBT was begun, following discussions between CARICOM, CARIFORUM, FAO, and various international assistance agencies.
The present CAP control strategy applied in the islands is based on use of flumethrin (Bayticol?), chosen as the acaricide in the eradication activities because it meets the requirements of effectiveness and interval application. It is applied to the back of the animal, from the withers to the base of the tail (as a pour-on), every two weeks. Although the technology used for the eradication activities is one of the safest available, it still relies on the use of a toxic substance, potentially hazardous to animals and the environment. Furthermore, the pour-on acaricide is difficult to apply to feral or unrestrained animals on a regular two-weekly basis.
The objective was to support an adaptive research programme that would build on a range of interventions at the regional level, in order to develop an alternative tick control programme, based in part on Integrated Pest Management (IPM) principles.
The alternative control and eradication technology
This
involved testing farmers’ adoption of sustainable and biologically
friendly alternative eradication techniques, such as use of:
- Duncan Self Medicating Applicators (DSMAs) (Figure 1);
- ACATAK – Biological Tick Development Inhibitor;
- biological control (using tick predators such as parasitoids, fungi or nematodes). This activity received further IFAD support through a small grant (TAG 507); and
- attractant pheromone decoy technology.
Adaptive research to validate control technology
Adaptive research on the new technologies was carried out in a number of field sites in the region to test its applicability to an eradication programme.
Following long delays in implementing the adaptive research component of CAP, which led to continual revisions to work plans, protocols, timetables and field sites, three technologies were finalized for testing and adaptation.
Use of Duncan applicators (large and small)
The
large populations of stray and uncontrollable livestock in many of the
islands were of great concern to CAP since most of these animals were
not receiving fortnightly treatments. The Duncan applicator had been used
successfully in Africa to control Rhipicephalus sp. in cattle and wildlife.
It was the opinion of FAO and IFAD that this technology had potential
value within CAP to target the free ranging and stray animals. However,
it was necessary to test the DSMAs under Caribbean conditions, particularly
the small applicators that had been developed to treat Ostriches, but
could be adapted to target small ruminants in the Caribbean (Figure
2). It was also the goal of IFAD that once these applicators showed
good potential, the technology would be transferred into the farming communities
so livestock owners would have full responsibility for using and maintaining
them.
Recent development of the growth inhibitor fluazuron, with a persistent effect of about 12 weeks, was considered a useful adjunct to fortnightly Bayticol treatment. Not only did it have the advantage of only needing three to four applications a year, but could also be important if Bayticol resistance were ever to develop on any of the islands – particularly those islands that had been using Bayticol before the eradication programme. The main constraint was that at the time it could only be used on non-dairy livestock, subject to the completion of ongoing extensive residue testing. Fluazuron had only been field tested on cattle against Boophilus microplus, so it was necessary to do further trials to test its efficacy against Amblyomma variegatum on cattle, and also on small ruminants.
The
investigation and adoption of biological control as an element of adaptive
research was in line with IFAD’s strategy for supporting non-chemical,
environmentally neutral tick control techniques. Following consultations
with scientists at CAB International, it was decided to focus the work
on development of myco-acaricides as an alternative control technology.
Myco-acaricides are environmentally friendly acaricides based on fungal
pathogens. They were considered advantageous because they could be applied
using conventional methods (pour-on or spray), were easily mass produced,
and could be stored for long periods. Furthermore, myco-acaricides had
potential to self-propagate in the field and therefore might not require
as intensive a treatment schedule as Bayticol. Laboratory bioassays to
assess the potential of several pathogens demonstrated a high lethal effect
from several isolates of Metarhizium anisopliae against Boophilus microplus
adults and larvae. Egg production and viability were also curtailed. Several
formulations were also assessed and an oil-based formulation was found
to give the best results. Field trials were developed to adapt the technology
to on-farm conditions. These trials showed that more than 50% of engorged
ticks demonstrated symptoms, showing that they were infected even though
the diseases symptoms caused by the pathogen are not expressed until ticks
are off the hosts. Other significant effects include a substantial reduction
in egg production and viability. The results have also shown that temperature
might be an important factor. However, subsequent laboratory studies have
identified an isolate of Metarhizium anisopliae which is effective at
a higher temperature (Figure 3). This isolate was to
be further assessed under field conditions.
Use of decoy tags within CAP was considered at the design stage to be
the first priority of the adaptive research programme. However, the work
did not take off because of lack of the necessary information from the
University of Florida about the development and use of the tags. Therefore,
it was decided at the 6th Amblyomma Program Council (APC) meeting (April
1999) to remove the pheromone decoy trials from the work plans.
