The avian tick Argas (Persicargas) arboreus is a vector of pathogens infecting the nestlings of the agriculturally beneficial bird, the buff-backed heron in Egypt. The topical treatment of the fed-mated (engorged) female A. (P.) arboreus with a sublethal dose of abamectin (10 µl 10 ppm/female) on the 3rd day after feeding (daf), reduced the concentration of total protein in the haemolymph (HL) by 13–66%, in the ovary by 30–54%, and in freshly deposited eggs by 11–16%, compared to untreated females during vitellogenesis and oviposition. However, the treatment did not prevent vitellogenesis and oviposition but reduced the number of mature oocytes (stages III–V) and deposited eggs. Additionally, it delayed the onset and slowed the progress of each process in the treated females. The application of abamectin at the onset of vitellogenesis (on the 3rd daf) in normal female and the prominent decrease inHL total protein concentration in treated female on the 4th daf pointed to a probable interference of abamectin with the release of the vitellogenesis-inducing factor (VIF) and/or other subsequent hormone(s) known to regulate vitellogenesis in this argasid tick species. Graphical abstract