Ishaaya, I., Division of Entomology, Agricultural Research Organization, Volcani Center, Bet Dagan, 50-250, Israel

S,S‐Di‐isobutyl N ethylethylenebis(thiocarbamate) (R‐31026) had a strong morphogenetic effect, acting by contact on the newly formed pupae of Tribolium confusum and Tribolium castaneum and thereby disrupting adult development. At a dietary concentration of 20 mg kg−1, 95% of pupae of T. confusum produced pupa‐adult intermediates; T. castaneum pupae were affected to a smaller extent. Topical application with 0.002 μg per 0–24‐h‐old pupa of T. confusum resulted in the formation of 88% malformed intermediates. The larvae brought into contact with R‐31026 were not affected and pupated normally, hence the compound differs in its activity from that of a typical juvenile hormone compound. On the other hand, the pupal morphogenetic activity of R‐31026 resembles that of the typical juvenoid compound 3‐[5‐(4‐ethylphenoxy)‐3‐methylpent‐3‐enyl]‐2,2‐dimethyloxirane (R‐20458). The progeny of the emerging adults from pupae treated with either R‐20458 or R‐31026 were strongly affected. The effective dosages were far below those required for pupal morphogenetic activity. Biochemical studies showed an increase in the soluble protein fraction during the pupal stage after treatment with either R‐31026 or R‐20458 indicating disturbances in protein build‐up. The bis(thiocarbamate) R‐31026 has more favourable practical properties than R‐20458 for controlling agricultural insects, because it does not prolong the larval feeding stage. Copyright © 1982 John Wiley & Sons, Ltd