2013 Annual Report
1a.Objectives (from AD-416):
Evaluate the resistance profile of cattle tick strains, and identify the presence of point mutations (PM) in cattle tick larvae.
1b.Approach (from AD-416):
Perform in vitro bioassays to determine susceptibility of four laboratory strains to ten acaricidal compounds with the Larval Tarsal Test (LTT); susceptibility to ivermectin of an ivermectin-resistant strain and susceptibility to fipronil of a fipronil-resistant strain using the Larval Packet Test (LPT); and susceptibility to ivermectin of an ivermectin-resistant strain using the Klafke Larvel Immersion Test (LIT). LC50s will be calculated from which resistance ratios will be estimated based on the comparison with a susceptible reference strain (Munoz). Molecular bioassays will be either run individually or investigated through a multiplex PCR newly developed in the CFTRL. Thirty larvae per population will be analyzed individually. The presence and frequency of the point mutation in these field strains will be compared with in vitro results on their resistance status previously assessed with the LTT. For some of the strains, if the presence of a point mutation is identified, there will be the possibility to investigate the frequency of the mutation among larvae having survived or died at a specific dose of flumethrin and cypermethrin.
This research established that the new LTT bioassay was able to reliably detect and measure the magnitude of resistance in cattle fever ticks to many different classes of pesticides. This is significant in that the LTT requires less labor and provides more information than traditional bioassay techniqes. This will be the technique used to test all future outbreak strains collected along the Texas/Mexico border and will provide much more information regarding the magnitude of resistance in collected strains with less labor.