“…Using the representation of integral terms in the structure of control signals as regulators with unlimited after-effect (Anan'evskii & Kolmanovskii, 1989;Andreev, 2009), the motion of CONTACT Olga Peregudova peregudovaoa@gmail.com mechanical systems with these types of regulators can be modeled by Volterra integro-differential equations (Volterra, 1959). Such equations arise in the mathematical modelling of viscoelastic materials (Dafermos & Nohel 1981;Mac 1977;Sergeev 2007b;Volterra, 1959), population dynamics (Britton 1990;Volterra 1959), agedependent epidemic of a disease (El-Doma, 1987), nuclear reactor dynamics (Kappel & Di, 1972). The study of the qualitative theory of Volterra integro-differential equations including the stability problem attracts great attention of numerous researches, see for instance Burton (1983), Grimmer and Seifert (1975) and Sergeev (2007aSergeev ( , 2017 and their bibliographies.…”