Here are two obituaries of David Saunders.

Obituary - David S. Saunders: man of insects and photoperiodism (Journal of Comparative Physiology A)
Helfrich-Förster, C. David S. Saunders: man of insects and photoperiodism (1935–2023). J Comp Physiol A (2023). https://doi.org/10.1007/s00359-023-01665-3 This is an open access article, and a pdf version may be downloaded here.

Obituary - Professor David Stanley Saunders (Antenna)
Here's a pdf of a proof copy of the obituary published in Antenna, the journal of the Royal Entomological Society, which is not open access.