Comparative biology of the tropical and temperate species of Rhipicephalus sanguineus sensu lato (Acari: Ixodidae) under different laboratory conditions

• Published in: Ticks and tick-borne diseases 2017-01, Vol.8 (1), p.146-156
• Main Authors: Labruna, Marcelo B, Gerardi, Monize, Krawczak, Felipe S, Moraes-Filho, Jonas
• Format: Article
• Language: English
• Subjects: Animals; Brazil; Climate; Female; Life Cycle Stages; Nymph; Photoperiod; Rhipicephalus sanguineus - physiology; Species Specificity
• ISSN: 1877-959X; 1877-9603
• DOI: 10.1016/j.ttbdis.2016.10.011

Recent studies have shown that the taxon Rhipicephalus sanguineus sensu lato (s.l.) is represented in Latin America by two distinct species, designated as 'tropical species' (distributed from Mexico to Brazil) and 'temperate species' (restricted to the southern cone of South America). Since both tropical and temperate species of R. sanguineus s.l. are parasites primarily of domestic dogs, the reasons for their distinct geographical distribution in South America could be related to particular requirements of abiotic conditions for off-host development. With the purpose to test this hypothesis, this study evaluated the off-host developmental stages (eggs, engorged larvae, nymphs and females) of both tick species simultaneously inside incubators with temperature and photoperiod regimens that simulated the summer and winter conditions of tropical Brazil (where the 'tropical species' occurs) and temperate Brazil (where the 'temperate species' occurs). Results showed that the temperate species had significantly higher survival rates than the tropical species, when engorged ticks (larvae, nymphs and females) and eggs were incubated at lower temperatures simulating winter seasons of many parts of the southern cone of South America, where the temperate species is known to occur. These results suggest that the absence of established populations of the tropical species in temperate areas of South America is related to the low overwinter capacity of the tropical species in those areas. Regarding the temperate species, unfed adults that molted from nymphs under summer conditions of either tropical or temperate Brazil remained dormant, at the state of behavioral diapause for at least 20 weeks. Contrastingly, when engorged nymphs of the temperate species were held at winter conditions for at least 3 months, and then transferred to summer conditions to complete molting, no diapause was observed in adult ticks. These results were corroborated by infestation trials, which showed that diapausing adult ticks took more days to attach to rabbits, and did in lesser numbers, when compared to nondiapausing adult ticks. Contextualization of our results in the current literature suggests that absence of established populations of the temperate species in tropical Brazil is linked to the fact that adult ticks would become inactive (diapause) right after molting from nymphs at any period of the year. On the other hand, absence of established populations of the tropical species in temp