Chemical structure, juvenile hormone activity and persistence within the insect of juvenile hormone mimics for Rhodnius prolixus

Abstract

41 chemicals were tested for juvenile hormone (JH) activity for Rhodnius prolizus by two methods of application. Several different classes of chemical were represented, viz. long chain terpenoid compounds, aryl terpenoid compounds, aryl terpenoid amines and aryl terpenoid ethers. All classes of chemical contained members which showed at least moderate activity. The most active compound was N-(2,5-dichlorophenyl)-3,7-dimethyl-2,6-octadienylamine; 0.0024 μg induced the production of an insect which was halfway between a normal adult and a complete supernumerary larva. Since several compounds with widely differing chemical groupings showed high JH activity, it is considered that overall molecular size and shape are important considerations in determining JH activity, although they do not by themselves provide a complete explanation. Some chemicals tested are specific in their JH activity to relatively few insects. JH mimic specificity is discussed and it is considered that molecular shape can explain some aspects of this phenomenon. The persistence within the insect of the JH mimics varied greatly. In general, compounds with a methyl ester group at one end and an epoxide group at the other had least persistence. The absence of one or more of these features tends to induce greater persistence. Within most classes of chemical, the members with highest JH activity tended to have least persistence and it is considered that the major factor affecting persistence with the insect is the rate of enzymic degradation of the JH mimic.