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

Abstract

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.

Keywords: eradication; fever tick; quarantine; tick garden.

Fig. 1.

Tick garden with Silverleaf Nightshade (Solanum elaeginifolium).

Fig. 2.

Tick garden with Buffelgrass (Pennisetum ciliare).

Fig. 3.

Engorged female B. microplus digging the soil to lay eggs.

Fig. 4.

Regression of stage interval length (in days) against temperature measured in degree-days (DD). A) Boophilus annulatus egg stage duration vs total DD (r² = 0.88). B) Boophilus annulatus larval stage duration vs. mean DD (r² = 0.61). C) Boophilus microplus larval stage duration vs. total DD (r² = 0.77). D) Boophilus microplus egg stage duration vs. total DD in exposed habitat (r² = 0.25). E) Boophilus annulatus larval stage duration vs. total DD (r² = 0.85). F) Boophilus microplus egg stage duration vs. total DD in canopied habitat (r² = 0.22).