Degree-days and off-host longevity of cattle fever ticks, Boophilus spp. (Acari: Ixodidae) in south Texas pastures.

Cattle fever ticks, Boophilus microplus (Canestrini) and Boophilus annulatus (Say), are native to Eurasia and have invaded the New World as vectors of bovine Babesiosis. Due to severe losses in livestock production, an eradication program by the USDA was established. Premises infested with Boophilus ticks are subject to regulatory oversight that includes acaricide treatment and quarantine. The quarantine duration varies between summer through winter and is based on the available information on the persistence of the off-host stages in pastures far from south Texas. The objective of this study was to assess the specific effect of thermal stress measured in degree-days on the longevity of B. annulatus and B. microplus off-host stages in south Texas pastures. Our results demonstrate that the longest off-host persistence for B. annulatus was 142 days under canopied habitat in the winter and 130 days in the summer. On the other hand, B. microplus off-host persistence was 113 days under canopy and 103 days in exposed habitat, both in winter. The results indicate that temperature was a key variable that prolonged the survival of B. annulatus but not B. microplus. In areas such as south Texas at the northernmost extent of B. microplus range, where mild winters prevail, we found a maximum persistence of less than 4 months (113 days), very close to the previous published record of 116 days. A reduction in the Texas pasture quarantine period from 9 months to 6 months would be justified for this species.

Interaction between anti-tick vaccine and a macrocyclic lactone improves acaricidal efficacy against Rhipicephalus (Boophilus) microplus (Canestrini) (Acari: Ixodidae) in experimentally infested cattle.

The southern cattle fever tick (SCFT) Rhipicephalus (Boophilus) microplus, is considered the most important ectoparasite of livestock in the world because of high financial losses associated with direct feeding and transmission of the hemoparasites Babesia bovis, B. bigemina, and Anaplasma marginale. Unfortunately, SCFT in many parts of the world have evolved resistance to all market-available pesticides thus driving development of new control technologies. Vaccination against ticks using the tick gut protein Bm86 has been shown to be effective against acaricide-resistant ticks. This technique has been successfully implemented in Puerto Rico for the control of acaricide-resistant R. microplus on dairy and beef cattle. Observations from Puerto Rico indicate a potentially positive interaction between anti-tick vaccination when used in conjunction with systemic acaricide treatment. In this project, controlled animal studies were completed directly comparing efficacy of anti-tick vaccination with and without systemic acaricide. Results show that the Bm86 anti-tick vaccine in combination with the macrocyclic lactone, Moxidectin, expressed a synergistic interaction, providing greater and longer efficacy than either treatment alone.