Capacidade de sobrevivência do embrião de Rhipicephalus (Boophilus) microplus (Canestrini, 1887) (Acari: Ixodidae) a diferentes períodos de exposição em temperaturas extremas em condições de laboratório

Abstract

Embryogenesis is one of the key events in the development of arthropods, especially when it occurs in the environment, such as ticks. Very little is known about embryo development in ticks and even less as the environment acts on this process. Among abiotic factors, temperature is known to interfere primarily in the metabolism, and to often limit the development of animals. Hence knowing the role of temperature in the embryogenesis of ticks is an important consideration, since it could be another tool in the formulation of strategies for control programs. Considering its importance and the lack of knowledge regarding its performance in relation to temperature variations which can occur during embryonic development, experiments under controlled laboratory were simulated – tests in which the embryo of Rhipicephalus (Boophilus) microplus underwent different times of exposure in extreme temperatures. Engorged females collected from cattle were cleaned, weighed, identified, placed in Petri dishes and transferred to camera heated BOD. After the third day of laying, were formed, in the Petri dish, nine groups (18, 27 and 32°C / 6, 12, 24 and 36 hours) of mass of eggs kept at 27 °C. On the 15th day of incubation, plates were placed in their respective temperatures/times. From each treatment, daily aliquots of eight mg of eggs were collected and fixed in 70% alcohol. Subsequently, the eggs were cleared in lactophenol and again returned to 70% alcohol. Through temporary mounting on excavated slides covered with coverslips, and with the aid of optical microscope examination, the exam for the presence and percentage of eggs with rectal sac – the first resulting structure of embryonic development – will be conducted. The images of the eggs of R. (B.) microplus was obtained through a video camera attached to a light microscope and stereoscope with a final increase of 400 and 100x, respectively, in order to record possible changes in the morphology of the egg or embryo. The incubation period of the eggs of R. (B.) microplus used in this experiment was up to 24 days. In all treatments was possible to observe the presence of rectal sac by optical microscopy. From the results obtained in this experiment conclude that embryos of R. (B.) microplus exposed for long periods to extreme temperatures did not present their embryonic development altered.