Off-host development and survival of Rhipicephalus (Boophilus) microplus in the Brazilian semiarid

Rhipicephalus (Boophilus) microplus is the most economically important tick of the world, including Brazil. Whereas the epidemiology of R. microplus is well known in most of the Brazilian land, virtually nothing is known from the Brazilian semiarid region, the Caatinga biome. Considering the relevance of R. microplus for the cattle industry within the Caatinga, this study aimed to evaluate for the first time the off-host development of this tick species under natural conditions of the Caatinga. During 2011-2015, engorged females of R. microplus were exposed to field conditions of native Caatinga, where female oviposition, egg incubation and hatching, and larval survival were quantified. In parallel, counterpart ticks (control group) were evaluated under optimal conditions in the laboratory. During the study, nearly 100% of the engorged females of the control group successfully oviposited fertile egg masses, from which most of the eggs yielded larvae (mean % hatching usually>90%). Under field conditions, while almost 100% of the engorged females oviposited, in most of the times no larvae hatched from these eggs. Furthermore, when larvae hatched, mean % hatching was most of the times <50%. Soil temperatures did not oscillate drastically through the study, with mean temperature between 30 and 35°C in most of the time. In contrast, rainfall was irregular throughout the study. Correlation analyses indicated that either the number of egg masses that yielded larvae, or the mean % hatching of the egg masses were positively associated with higher rainfall months. Our results showed that in most of the time, field conditions were unfavorable for R. microplus, indicating that cattle would have a low exposure to R. microplus infestations when raised in Caatinga fields like those of the present study.