Ground-based imaging spectroscopy of terrestrial planets is a powerful tool for monitoring the spatio-temporal variability of minor atmospheric species. Instantaneous mapping of planetary disks allows us to study transient phenomena and variations with local time and longitude, which are not easily observed by an orbiter in space. We have been using the TEXES (Texas Echelon Cross Echelle Spectrograph) imaging spectrometer at the NASA Infrared Telescope Facility (Maunakea Observatory, Hawaii) for two long-term observing campaigns: (1) monitoring of H2O2 and HDO on Mars (since 2001) and (2) monitoring of SO2 and HDO on Venus (since 2012). In both cases, HDO is used as a proxy of H2O. The Mars data have allowed us to study the seasonal variations of H2O2 on Mars (Encrenaz et al. A&A 627, A60, 2019). The Venus data have revealed that SO2 and H2O behave very differently at the cloudtop of Venus. Whereas H2O maps are globally uniform, SO2 shows strong spatial and short-term variations, with a time scale of a few hours (Encrenaz et al. A&A 623, A70, 2019 & EPSC 2019). These campaigns are performed in support to Mars Express and TGO on Mars, and Venus Express and Akatsuki on Venus.