Efeito do microambiente sobre a sobrevivência e o número de larvas produzidas por fêmeas do carrapato Rhipicephalus linnaei (ACARI: IXODIDAE)

Abstract

Among the ticks of greatest veterinary and medical importance, the cosmopolitan species Rhipicephalus sanguineus sensu lato stands out. Although it is an occasional parasite of humans, it is a habitual ectoparasite of domestic dogs and acts as a vector of potentially lethal pathogens. In South America, this complex is represented by two distinct species: Rhipicephalus sanguineus sensu stricto and Rhipicephalus linnaei, which differ in genetic, behavioral, and ecological aspects. The tick R. linnaei completes its non-parasitic life stage in anthropized and dry environments, but notably not in green areas. However, the abiotic factors that prevent its development in these natural environments are not yet understood. This study compared the influence of abiotic variables (temperature and relative humidity) from different environments on the life cycle of R. linnaei, focusing on engorged female ticks, oviposition, egg hatching, and larval longevity. The microenvironments evaluated were: a green Cerrado area (Cerradão), an apartment, an urban backyard, and a laboratory environment used for colony maintenance, which served as control. Engorged females were placed monthly, over 36 months, in these environments, confined in metallic envelopes and evaluated daily. Temperature and relative humidity were recorded hourly in all microenvironments. In anthropogenic environments, the backyard and apartment, the life cycle was interrupted in 62% and 27% of releases, respectively. In the backyard, this interruption occurred predominantly during the dry season; in the apartment, it was restricted to this same period. In contrast, in the forest environment, the cycle was compromised in 33% of releases, almost exclusively during the rainy season. Larval production, a parameter encompassing oviposition and egg hatching, showed greater sensitivity to mean relative humidity below 60%. Larvae themselves demonstrated even higher susceptibility, with significant survival reduction observed when mean relative humidity was below 80%. Larval longevity was affected in all three natural microenvironments, with lifespan reduced to less than one-third of that observed in the BOD incubator. While average larval survival in this controlled environment was approximately 90 days, it was reduced to 30 days or less in the other environments. Based on these results, we suggest that R. linnaei relies on behavior seeking favorable microenvironments and frequent host presence to maintain its life cycle in anthropized environments. In green areas, larval movement is compromised by higher humidity, milder temperatures, and frequent absence of hosts.