ARS | Publication request: Laboratory evaluation of verbutin as a synergist of acaricides against larvae of Rhipicephalus (Boophilus) microplus (Acari: Ixodidae)

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 22, 2010
Publication Date: August 10, 2010
Citation: Li, A.Y., Davey, R.B., Miller, R. 2010. Laboratory evaluation of verbutin as a synergist of acaricides against larvae of Rhipicephalus (Boophilus) microplus (Acari: Ixodidae). Journal of Economic Entomology. 103(4):1360-1364.

Interpretive Summary: Acaricides play a pivotal role in preventing the reintroduction of the cattle fever tick from Mexico through cattle importation. Resistance to key acaricides poses a major threat to the continued success of the Cattle Fever Tick Eradication Program. Synergized acaricide formulations may help eliminate resistant ticks from infested cattle. A study was conducted to evaluate the synergistic effects of verbutin to three commonly used acaricides (coumaphos, permethrin and amitraz) against both susceptible and resistant tick strains. Results of bioassays indicated that verbutin was more potent than PBO, a commonly used synergist, in increasing toxicity of both coumaphos and amitraz against resistant tick larvae. Verbutin was also found to be equally effective as PBO in increasing permethrin toxicity. The findings from this study suggest that verbutin has the potential to be used as a synergist in developing new synergized acaricide formulations that can be effective against resistant tick populations.

Technical Abstract: Synergistic effects of verbutin, a member of aryl alkynyl derivatives, to three commonly used acaricides were evaluated with the modified Food and Agricultural Organization Larval Packet Test (FAO-LPT) against both susceptible and resistant strains of the southern cattle tick Rhipicephalus (Boophilus) microplus. These tick strains demonstrated various levels of resistance to coumaphos (2.5 – 8.2 x), permethrin (57.9 – 711.7 x) and amitraz (3.5 – 177.5x). Verbutin alone was more toxic to tick larvae than piperonyl butoxide (PBO), a conventional pesticide synergist. With synergism ratios (SR) ranging from 1.5 to 6.0, verbutin was more potent than PBO (SR = 0.9 – 1.6) in synergizing coumaphos toxicity to resistant tick larvae. Similarly, verbutin (SR = 1.8 – 15) was also found to be more potent than PBO (SR = 0.9 -2.5) in synergizing amitraz in resistant tick strains. Both verbutin and PBO significantly increased permethrin toxicity to larvae of all tick strains tested, and there was no significant difference between the two synergists. SRs ranged from 2.1 – 4.4 and 2.1 – 3.6 for PBO and verbutin, respectively.