He+ density depletions, considered as originating from equatorial plasma bubbles, or as fossil bubble signatures, were involved in this study. They were detected from ISS-b spacecraft data (1978-80, F10.7~200) in the topside ionosphere (~1000 km) deeply inside the plasmasphere (L~1.3-3) (Sidorova, ASR, 2004, 2007). (1) There are some questions about the survival possibilities of plasma bubbles at the altitudes of the upper topside ionosphere (1000 km and more). The estimation of the characteristic times of a life, diffusion and vertical drift transport of helium ions (He+) at the topside ionosphere heights of the low-/mid-latitude region was made. (2) It is suggested that the equatorial F region irregularities, their post sunset development, evolution, and decay processes are controlled by the sunset electrodynamics of the equatorial region. He+ density depletion occurrence probability was considered in connection with equatorial F-region irregularities (EFI), equatorial F-spread (ESF) and plasma bubbles (PB). So, the seasonal and longitudinal (s/l) variations of their occurrence probabilities were compared. The s/l variations of depletion statistics were obtained under winter, summer and equinoctial condition in the interval of 25-50 deg. INVLAT for Southern and Northern Hemispheres. EFI statistics were taken from (McClure et al., JGR, 1998), (Basu et al., Radio. Sci., 1976), (Su et al., JGR, 2006), based on AE-E, OGO-6 and ROCSAT data respectively. Moreover, ESF and RSF (range spread-F) statistics, obtained (Maruyama and Matuura, JGR, 1980, 1884) from ISS-b data, and plasma bubble statistics, obtained (Watanabe and Oya, JGG, 1986) from Hinotori data (1981, 650 km), were also taken for comparison. EFI, ESF (RSF) and plasma bubble statistics were obtained above the equatorial region within +-20 deg. DIPLAT under the same solar activity conditions. It was revealed that the main statistical maxima of the mentioned above equatorial F-region irregularities are well enough reflected in the s/l statistical plots of the He+ density depletions of the both hemispheres. The best conformity was obtained during the equinox periods, the worst one – during solstice periods, when the most dramatic insolation differences take place for the different hemispheres. (3) According to publications, He+ density depletion cases were also revealed on OGO-4, OGO-6, Oreol-1 and DE-2 spacecraft data. They occur during high and maximal solar activity, when He+ density layer is very well developed in the topside ionosphere (Wilford et al., JGR, 2003). Using the model of the plasma bubble formation as suggested by Woodman and La Hoz (IGR, 1976), it was concluded that the topside plasma bubbles, seen in He+ density, are rather typical phenomena for the topside ionosphere for high solar activity epoch.