|AHRENS, ELMER - RETIRED, MCALLEN, TX
Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/21/1998
Publication Date: N/A
Interpretive Summary: Current technology for eradication of the fever tick from the quarantine zone along the Texas-Mexico border is expensive, labor intensive and presents environmental hazards because of the large quantities of acaricides used in dipping vats. We have developed an injectable microsphere (IMS) formulation containing ivermectin to provide long-lasting gcontrol of ticks and other livestock pests. When cattle were treated with a subcutaneous injection of the IMS formulation, no engorging females could be found by the end of the first month postinjection. In contrast, large numbers of ticks remained on control cattle throughout the 16-wk study. A few ticks were collected from sentinels placed in the treated pasture during wk 7-8, but 10 times as many were collected from the sentinels in the pasture containing controls. No ticks were collected from sentinels placed in the pasture containing treated cattle during wk 11-12 and 14-15 posttreatment, but large numbers were collected from the control pasture. Thus, the IMS formulation not only controlled ticks on the treated cattle, but eliminated the ticks from the pasture in which they were held. Treated cattle gained an average of 35 kg more than the untreated controls. The IMS formulation should be useful for control of a variety of pest of livestock, exotic game, and pets.
Technical Abstract: Two groups of 6 Hereford heifers infested with B. annulatus (Say) were held on separate 7 ha, tick-infested, buffel grass pastures. Cattle in one pasture were injected subcutaneously in the neck with a controlled-release microsphere formulation of ivermectin at the rate of 2.4 mg(AI)/kg body weight and a control group was injected with carrier only. Beginning 4 wk post-injection, continuing throughout the remainder of the test (16 wk), n engorged ticks (>5.5mm) were found on the treated cattle, while large numbers of ticks remained on the untreated controls. A few ticks were recovered from untreated sentinel animals placed in the treated pasture during wk 7-8 posttreatment, but none were recovered from animals exposed from wk 11-12 or wk 14-15. Untreated sentinel cattle placed in the control pasture during these periods produced large numbers of Boophilus ticks. Although the cattle, pastures, and tick habitat were about equal, treated cattle gained an average of 77 kg compared to an average of 42 kg for the control group during the study. This technology offers a possible alternative to the current program of dipping and vacating pastures for eradication of Boophilus sp. from the quarantine zone in So. Texas. Larger scale testing is needed to determine the potential of the injectable microsphere formulation and to optimize its use in eradication or control strategies.