Estudo do comportamento de queda de fêmeas ingurgitadas do carrapato Boophilus microplus (Canestrini, 1887) (Acari:Ixodidae)

Abstract

A description of the drop-off behaviour of engorged females of the tick Boophilus microplus was carried out as a result of an experiment at the Experimental Station, Embrapa Gado de Leite, Coronel Pacheco, MG, Brazil. Its objective was to evaluate any repercussions of changing the time of milking of cattle in terms of reduced recontamination of the pastures with the tick. Such possible changes in this daily cattle management routine have recently become a reality since the advent of refrigerated on-farm storage of the milk and non-daily collection by tanker truck. The field experiment consisted of a phase in summer, with a longer photoperiod, and in winter, with a shorter photoperiod. Twelve weekly experimental repetitions, of 24 hours duration, were carried out in each of these seasons. For each repetition, eight non-lactating, 7/8 Holstein-Friesian x Zebu cows, naturally infested with B. microplus and maintained on pastures, were removed to an experimental area on the day on which the observations were to be made and maintained in individual stalls. At each hour, over 24 hours, all fully engorged ticks that had dropped off naturally from the cattle were collected from the stalls. The results showed a significant difference in the rhythm of their drop-off in the summer compared to winter. In the summer the greater proportion of ticks dropped off between 07:00 and 10:00 (35.3%) with a maximum at 09:00. In winter, there were two daily periods of greater drop-off of ticks, the first between 06:00 and 09:00 (19.69%) with a maximum at 06:00, and the second between 14:00 and 17:00 (21.79%) with a maximum at 15:00. The percentage of ticks dropping off during the traditional milking time (05:00-08:00 and 13:00-16:00) would have been 35.15%, while those falling during an alternative sytem under consideration for Central Brazil (08:00-11:00 and 16:00-19:00) would be 45.48%, during the summer. During the winter, the proportion of ticks falling from the cattle is 40.51% and 32.71% for the two times of milking, respectively. Considering the time that the animals remain in stalls for feed supplement during the period between milkings during the dry season (May to September), the proportion of ticks falling would be 55.83% for the traditional system (05:00-16:00) and 52.36% for the milking period under consideration (08:00-19:00). The correlation between drop-off of ticks and photoperiod was significant only for the summer, but not so for mean air temperature nor relative humiditty for either of the seasons compared.