Histopathological effects of the fruit extract of Citrullus colocynthis on the integument of the female tick Hyalomma dromedarii

Hyalomma dromedarii is a hard tick species parasitizing domestic animals, particularly camels. Heavy infestation results in huge economic losses through severe blood loss and transmission of pathogens, in addition to crucial problems for camel production. Worldwide control of ticks is mainly based on acaricides, which have led to environmental pollution, resistance development, and an increase in the cost of control. To reduce the drawbacks of chemical acaricides, new tick control methods are therefore required, such as the application of natural plant extracts. Citrullus colocynthis, commonly known as bitter apple, is a desert plant found in Egypt. It has an economic importance due to its bioactive compounds with antidiabetic, antimicrobial, and potentially anticancer properties. In addition, it is used as a natural preservative, as it was historically applied to protect Egyptian manuscripts and leather from fungal damage. The goal of this work was to study the histopathological and ultrastructural changes of H. dromedarii integument after immersion in 100 mg/mL of C. colocynthis ethanolic extract. Volatile components of the extract were detected following the use of gas chromatography-mass spectrometry (GC-MS). Light, scanning, and transmission electron microscopy examinations provided evidence that C. colocynthis caused great damage to the integument. Increasing eroded areas with irregular folds and warts were observed by SEM. LM and TEM showed integumental layers separation, procuticle disorganization, subcuticular layer rupture and epidermal layer damage. GC-MS revealed volatile constituents, such as methyl linoleate, octadecadienoic, palmitic, and stearic acids. This is the first histological investigation that reported the integumentary damage caused by C. colocynthis in H. dromedarii. The present data suggest that the changes in all integument layers of the female tick H. dromedarii following treatment with C. colocynthis extract may facilitate the transport of toxic compounds into ticks' internal systems, which can then affect other organs. As a result, C. colocynthis can be considered as a promising tick control agent.