Estudos bioquímicos comparativos dos ovos de Rhipicephalus (Boophilus) microplus (Acari: Ixodidae) durante a oviposição

Abstract

To fill some gaps about the intrinsic mechanisms of the biology of oviposition of R. (B.) microplus, we evaluated the concentration of lipids and carbohydrates, as well as the variability of lipid in eggs per day of posture. For this, engorged females weighing between 151 and 360 mg were placed in controlled environment (27 ± 1 ° C, 80 ± 5% RH, darkness), and after beginning of laying, three samples of the eggs pool were daily collected, packed and preserved at -20 º C. Samples 1 and 2, weighing 50 mg each, were used to quantitate lipids and glucose, and to evaluate the lipid profile, respectively; and the third sample, containing 1 g of eggs, was used to quantitate glycogen. The determination of total lipids was performed using phospho-vanillin reagent, while the concentrations of cholesterol, triglycerides and glucose were obtained by colorimetric determination using endpoint enzymatic kit. The level of glycogen was performed using the acid 3,5 dinitrosalicylic reactive . The results were analyzed by nonparametric Kruskal-Wallis and the relationship between the concentrations of substrates and the days of laying was assessed by polynomial regression. There was no significant difference in the concentrations of these substrates in eggs from different days of oviposition, as there was no relationship of these concentrations with the days of laying. After lipid extraction, the samples were performed in thin layer chromatography, high-performance (HPTLC) for neutral lipids and phospholipids. Then, densitometry was performed using the Image Master Total Lab and the daily percentage of each lipid in the samples was calculated. Among the neutral lipids were identified the hydrocarbons, esterified cholesterol, triglycerides, fatty acids, free cholesterol and diacylglycerol. Of these, the cholesterol ester showed the highest variation, it was not detected in eggs at the fifth day of oviposition. Among the phospholipids were detected the phosphatidic acid, phosphatidylethanolamine, phosphatidylcholine and sphingomyelin fosfatidilinusitol. This latter was absent in eggs of the seventh day onwards. Thus, the different rates of hatchability of eggs from different laying days cannot be attributed to the concentrations of total lipids, although some specific lipids such as cholesterol ester and sphingomyelin might influence the difference in larval hatchability, more researches are needed for clarify the role of these substrates in embryogenesis