Submitted to: Journal of Medical Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 7, 1999
Publication Date: N/A
Interpretive Summary: Populations of cattle tick with the ability to survive pesticide treatment have developed in Mexico. It is unknown what pesticides these ticks can tolerate, the highest level of exposure they can survive, or how they overcome the toxicity of these chemicals. The development of resistance in Mexican cattle ticks is of great concern to the United States. The cattle tick is not present in the U. S., but is common in Mexico. Mexican cattle ticks are kept out of the U. S. by inspecting all cattle imported from Mexico then treating them with pesticides. Resistance to pesticides renders the treatment of cattle less reliable and places a greater burden on inspection teams. In this study, the level of pesticide exposure required to kill resistant ticks was established for five different pesticides and four different populations of ticks. A general understanding of how these ticks survive exposure to specific pesticides was also achieved. This information will allow the APHIS scientists who treat Mexican cattle at the border to be aware that these resistant tick populations exist and to consider possible changes in their procedures. Scientists of the ARS will use this information to develop future research into the extent of the resistance problem, to find ways to control resistant ticks, and to develop resistant management programs that delay the onset of resistance in Mexico. Ultimately U. S. cattle producers benefit through reduced risk of cattle tick re-infestation and thereby suffer no production losses due to cattle fever ticks.
Two patterns of pyrethroid resistance were characterized from Boophilus microplus collected in Mexico. One was characteristic of a kdr mutation and the other involved esterase and cytochrome P450 enzyme systems. The kdr-like pattern, found in the Corrales and San Felipe strains, was characterized by very high resistance to several pyrethroid acaricides not synergized by TPP and PBO, and high resistance to the chlorinated hydrocarbon, DDT. Esterase and cytochrome P450-dependent resistance was found in the Coatzacoalcos strain. It was characterized by resistance to several pyrethroid acaricides synergized by TPP and PBO, but no resistance to DDT. The Coatzacoalcos strain also showed resistance to organophosphate (OP) acaricides. This factor appeared to be independent of pyrethroid resistance. Pyrethroid resistance patterns found in Mexico were similar to those found earlier in Australia. The significance of pyrethroid and organophosphate resistance to the U. S. cattle fever tick quarantine is discussed.