EFFECT OF LONG-CHAINED ESTERS ON THE INSECTICIDAL PROPERTIES OF L-CANAVANINE

The ability of the several esters of L-canavanine, a potentially insec ticidal natural product of leguminous plants, to enhance the potency o f the parent compound was evaluated with the propyl, butyl, isobutyl, and octyl esters of L-canavanine. These compounds, administered either by a single parenteral injection or by dietary consumption, were test ed for their intrinsic toxicity in studies conducted with terminal ins tar larvae of the tobacco hornworm Manduca sexta [Sphingidae]. Parente rally injected propyl or butyl esters were somewhat more toxic than ca navanine, but the isobutyl and octyl esters were far more deleterious to larval growth and development. A single injection of the isobutyl o r octyl ester (1.25 mg/g larva, molar equivalent of L-canavanine dose) was lethal to all the test animals before the end of the larval insta r. Much of the toxicity of the octyl ester arguably was due to release of octyl alcohol, since the free alcohol is highly pernicious. In con trast, the isobutyl ester was far more toxic than isobutanol. A differ ent picture emerged from chronic exposure to the tested esters via die tary consumption. By this administrative route, although all of the es ters were marginally more toxic than canavanine, the tested compounds exhibited much less toxicity than occurred by parenteral injection. Li ttle difference was noted in the relative growth-inhibiting activity b etween the esters, and all of the free alcohols exhibited little delet erious effect on larval development.