Submitted to: Veterinary Parasitology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/21/2006
Publication Date: 6/30/2006
Citation: Davey, R.B., George, J.E., Miller, R.J. 2006. Comparison of the reporductive biology between acaricide-resistant and acaricide-susceptible Rhipicephalus (Booplilus) microplus (Acari: Ixodidae). Veterinary Parasitology. 139:211-220. Interpretive Summary: In Boophilus ticks, although acaricide resistance is a world-wide problem, there is little information on the impact that resistance has on the reproductive potential of resistant ticks. The reproductive dynamics of an acaricide-susceptible strain of B. microplus was compared to strains resistant to organophosphate (OP), pyrethroid (P), and formamidine (F) acaricides to determine whether the acquisition of resistance to these chemicals caused any measurable reduction in fitness. The reproductive factors associated with the susceptible strain were remarkably similar to what has been reported for other susceptible strains throughout the world. The comparison between the susceptible strain and strains that were resistant to P or F chemicals showed little evidence of a reduction in fitness in either resistant strain. However, the comparison between the susceptible strain and an OP-resistant strain showed that the OP-resistant strain produced 30% fewer eggs per female than the susceptible females. Thus, the results of this study demonstrated that the acquisition of OP resistance dramatically reduced the reproductive potential of the resistant ticks. This reduction in reproductive potential in OP-resistant ticks could potentially be used as a tool in the development of management strategies for mitigating OP-resistance under natural conditions.
Technical Abstract: The reproductive dynamics of an acaricide-susceptible strain (SUS) of Boophilus microplus were compared to strains of ticks resistant to organophosphate (OP), pyrethroid (P), or formamidine (F) acaricides to determine whether the acquisition of resistance caused a reduction in fitness. The SUS strain had a preoviposition period of 3.0 d, an oviposition period of 12.1 d, an egg incubation period of 22.5 d, an average of 3,670 eggs per female, and an average percentage egg hatch of 78.1%, which was similar to other reports around the world. Reproductive dynamics of the P-resistant strain (PYR) and the F-resistant strain (FOR) were similar to those of the SUS strain, thus there was little evidence of a reduction in fitness caused by resistance to P or F acaricides. The OP-resistant strain (OPR) produced a number of statistical differences in reproductive factors in comparison to the SUS strain, although differences in egg incubation period and oviposition period were not great enough to indicate that the OPR strain was biologically less fit than the SUS strain. However, results indicated that the OPR strain was at a selective disadvantage compared to the SUS strain in the production of eggs, which was 30% less than the SUS strain. Thus, the acquisition of OP resistance caused a reduction in fitness associated with the resistant ticks.