Tychiorhinus subochraceus is a weevil species endemic to the island of St Helena, where it is restricted to the high altitude cloud forests. Recorded in both 2005 and 2018, this species requires further survey work. This species was found in association with cabbage trees: these could include Black Cabbage (Melanodendron integrifolium – VU), She-cabbage (Lachanodes arborea – EW) and He-cabbage (Pladaroxylon leucodendron – CR), which have a restricted distribution and introduced species at lower elevations. This species is not restricted to the cloud forest.

Populations in the cloud forest are under threat from climate change, invasive non-native species of trees and shrubs, as well as New Zealand Flax (Phormium tenax) (impacting host trees), invasive non-native invertebrates, and the recent spread of fungal diseases, including Phytophthora spp., on cloud forest trees, will seriously threaten this species. Populations present on non-native plant species are under threat from habitat deterioration and loss from drivers of change including climate change and invasive non-native species. Non-native vertebrate predators, such as rodents and the African Grass Frog (Strongylopus grayi) may also negatively impact this species. Its extent of occurrence (EOO) and area of occupancy (AOO) are both 16 km², it occurs in two locations (based on the threats), and it is experiencing ongoing decline in habitat due to the threats described above. This species is assessed as Endangered.

This species is endemic to the island of St Helena, in the South Atlantic Ocean, where it has only been found in the upper portions of the Green Heartland area. Wollaston (1877) recorded this species in the highest region of the island between Cuckhold’s Point/Mt. Actaeon/Diana’s Peak, near High Peak and lower at Cason’s. Fifteen specimens were recorded by H Roberts. During surveys in 1967, 193 specimens were recorded at the High Central Ridge, High Peak and Teutonic Hall. Decelle and Voss consider that this species is moderately abundant. Mendel, Ashmole and Ashmole recorded it from Cuckold’s Point, Diana’s Peak and High Peak (Mendel et al. 2008). This species was also recorded in 2013 from Upper Legg's Gut, southern branch, from leaf litter. It was last recorded in 2016 through the surveys of Pryce (2021) who collected eight specimens by Berlese extraction of dead wood and leaf litter and organic debris, from three sites along the High Central Ridge.

Note: there are historical changes with the site names for Diana’s Peak, Cuckhold’s Point and Mt Actaeon and as such, we are including all the names in this assessment for the location of the records; see St Helena Government (2020).

This species was recorded on St Helena in 1875 by Wollaston (1877). He recorded 38 specimens of this species in the highest region of the island between Cuckhold’s Point/Mt. Actaeon/Diana’s Peak , near High Peak and lower at Cason’s. Fifteen specimens were recorded by H Roberts. During surveys in 1967, 193 specimens were recorded at the High Central Ridge, High Peak and Teutonic Hall. Decelle and Voss consider that this species is moderately abundant. Mendel, Ashmole and Ashmole recorded it from Cuckold’s Point, Diana’s Peak and High Peak (Mendel et al. 2008). This species was also recorded in 2013 from Upper Legg's Gut, southern branch, from leaf litter. It was last recorded in 2016 through the surveys of Pryce (2021), who collected eight specimens by Berlese extraction of dead wood and leaf litter and organic debris, from three sites along the High Central Ridge.

It is associated with cabbage trees: these could include Black Cabbage (Melanodendron integrifolium – Vulnerable), She-cabbage (Lachanodes arborea – Extinct in the Wild) and He-cabbage (Pladaroxylon leucodendron – Critically Endangered) (Lambdon and Ellick 2016). Decelle and Voss (1972) recorded it from dead and rotting cabbage trees, under twigs and fallen cabbage tree leaves, and from sieving earth and rotten wood. It is considered linked to cabbage trees at higher elevations and on introduced species at lower elevations.

This species was recorded from cabbage trees: these could include Black Cabbage (Melanodendron integrifolium – VU), She-cabbage (Lachanodes arborea – EW) and He-cabbage (Pladaroxylon leucodendron – CR), which are found in the cloud forest of St Helena and also from leaf litter and other organic debris. The cloud forest host trees have ongoing threats including climate change, intense competition from invasive non-native plant trees, shrubs and other plant species, including New Zealand Flax (Phormium tenax). The recent arrival and spread of fungal tree diseases, including Phytophthora spp, on cloud forest trees will seriously threaten this species, although this may be preceded by a temporary boom in the beetles’ population if a large number of endemic trees die and decay, likely followed by a disastrous collapse. Species of non-native predatory invertebrates living in decaying wood, such as ants, rove beetles, spiders and centipedes, and saproxylic species that modify the dead wood habitat, such as powder-post beetles, millipedes and woodlice, are likely to impact this species negatively. Populations present on non-native plant species are under threat from habitat deterioration and loss from drivers of change including climate change and invasive non-native species. Non-native vertebrate predators, such as rodents and the African Grass Frog (Strongylopus grayi) may also negatively impact this species.

This species is on the Environmental Protection Ordinance on St Helena, which indicates protected species. The Peaks are currently within a protected area and part of the government’s Nature Conservation Area (NCAs). This species will benefit from the habitat improvement outlined in the Peaks National Park Management Plan (2019). There is currently no specific action plan for this species, but its conservation and further research will be supported through the St Helena Invertebrate Strategy 2023–2027 (St Helena National Trust and St Helena Government 2023).