Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/22/2004
Publication Date: 4/15/2005
Citation: Li, A.Y., Davey, R.B., George, J.E. 2005. Carbaryl resistance in Mexican strains of the southern cattle tick Boophilus microplus (Acari: Ixodidae). Journal of Economic Entomology. 98(2):552-556. Interpretive Summary: The USDA's Cattle Fever Tick Eradication Program (CFTEP) has successfully protected the United States from re-infestation of the Southern cattle tick, Boophilus microplus (Canestrini), by inspection and dipping treatment of all cattle imported from Mexico. Coumaphos, an organophosphate acaricide, is the only registered acaricide for use in the dipping vats. Development of resistance to coumaphos and other acaricides in cattle ticks in Mexico poses a major threat to the CFTEP. This study was conducted to evaluate the susceptibility of ticks to carbaryl, a carbamate acaricide with a mode of action similar to that of organophosphates. High levels of resistance to carbaryl were detected in several Mexican tick strains resistant to coumaphos. A significant cross resistance pattern was identified between carbaryl and coumaphos. The data indicate that it is unlikely that carbaryl will be effective in controlling cattle ticks resistant to coumaphos or other organophosphates. The results from this study would help in choosing the right acaricides to control resistant ticks in Mexico, or to eliminate outbreaks of cattle ticks within the quarantine zone along the US-Mexican border in Texas.
Technical Abstract: Resistance to carbaryl in six strains of the Southern cattle tick, Boophilus microplus (Canestrini), was evaluated with the Food and Agricultural Organization's larval packet test. The susceptible tick strains from the cattle fever tick quarantine zone in Texas were more susceptible to carbaryl than to coumaphos and diazinon. Compared to the susceptible reference (Gonzalez) strain, the Mexican tick strains demonstrated 10.9 to 59.5-fold resistance to carbaryl. Significant cross resistance was found between carbaryl and the organophosphate acaricides coumaphos and diazinon. Bioassay results with synergists suggested that metabolic detoxification mechanisms did not play a major role in carbaryl resistance. Resistance to carbaryl was likely conferred by insensitive acetylcholinesterase. The implications of carbaryl resistance in tick eradication and control are also discussed.