Light, scanning electron microscopy and SDS-PAGE studies on the effect of the essential oil, Citrus sinensis var. balady on the embryonic development of camel tick Hyalomma dromedarii (Koch, 1818) (Acari: Ixodidae).

GC-MSE analysis of the essential oil of fresh fruit peel of Citrus sinensis var. balady recognized two main natural toxic compounds, limonene (83.28%) as hydrocarbon compound and linalool (3.97%) as oxygenated compound. Therefore, the objective of this study was to evaluate its effect on different egg-ages of Hyalomma dromedarii at four concentrations of 1:40, 1:30, 1:20 and 1:15 (oil : ethanol 95%) (v/v). The LC50 values were 1:56, 1:34, 1:41, 1:32, 1: 23, 1:23, 1:18, 1:14 and 1:11 for egg-ages of 2, 4, 6, 9, 11, 13, 16, 18 and 20 day, respectively. Histological Examination (HE), Scanning Electron Microscopy (SEM) and Sodium dodecyle sulphate polyacrylamide gel electrophoresis (SDS-PAGE) were done on the 9th day old-eggs treated with the essential oil 1:32 (the LC50 value of 9 day old-egg). HE was done on the 11, 12, 13, 14 and 15th day old eggs; SEM was done on the 11, 15 and 17th day old eggs and SDS-PAGE was done on the 10, 11, 12, 13, 14, 15 and 17th day old eggs and compared each with those of control. In control, HE showed that nuclei migrated to the periphery and became part of the cytoplasmic membrane, blastula appears as a complete ring cells. Germ layer form and the later differentiate to different organelles such as opithosoma, ambulatory segment and chelicera...etc. while incase of treated eggs, HE showed that irregular manner of ectoplasmic membrane formed, blastula gathered on one or two sides, the cells of germ layer gather on one side as small or large mass or ring shape. Cells gathered as small masses or finger shape without forming any organelles. SEM revealed that heavy small bulging wrinkles were observed on egg shells of control. These wrinkles changed into large size in treated eggs on the 11th day and disappeared at the following days to become smooth surfaced. SDS-PAGE exhibited 15, 14, 14, 12, 17, 14 and 15 bands for treated eggs on the 10, 11, 12, 13, 14, 15 and 17th day old-eggs, respectively and 14, 15, 16, 19, 17, 19 and 18 bands for control eggs at the same egg-ages. The molecular weights of these bands were different in both control and treated eggs. It was concluded that the essential oil of C. sinensis var. balady has strong toxic effect on eggs of H. dromedarii especially in earlier embryonic development.