Abstract
The structure-activity relationship of various aliphatic, alicyclic, and aromatic mono- and bisisothiocyanates affecting the growth and development of the tobacco hornworm, Manduca sexta, larva was studied. While topical application of short-chain aliphatic monoisothiocyanates to thirdinstar M. sexta larvae did not affect larval development, aromatic mono- and diisothiocyanates were toxic within the dose range tested. Short-chain alkylene and alicyclic 1,3- or 1,4-bisisothiocyanate derivatives, however, prevented the formation of abdominal spiracles and of crochets on the abdominal prolegs at molts following treatment. Their ED 50 values for causing spiracular abnormalities ranged from 25 to 208 nmol/larva. Moreover, long-chain mono- or bisisothiocyanates with structural resemblance to known juvenoids had juvenile hormone activity in the black M. sexta assay (their ED 50 range from 0.12 to 4.8 nmol/larva) and, in some cases, the formation of supernumerary sixth-instar larvae was observed. Surprisingly, nonjuvenoidlike bisisothiocyanates derived from α-amino acids ornithine and lysine also showed charateristic juvenile hormone effect in this test system (the ED 50 values are 0.11 and 0.34 nmol/larva, respectively). The structural requirements for the two different types of activities as well as hypotheses about the possible mode of actions are also discussed.
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