Distribution and metabolism of two insect juvenile hormone analogs in colonies of the imported fire ant, Solenopsis invicta

Abstract

The distribution and metabolism of ¹⁴C-1-(6¹-7¹-dimethyl oct-2¹-enyl)4-ethyl phenyl ether (R-20458) and (2,3-³3H)-7-epoxy-1-(p-ethyl-phenoxy)-3-ethyl-7-methylnonane (R0-10-3108) were studied in small colonies of the imported fire ant. Formulations of each insect growth regulator, (IGR), in once refined soybean oil were presented to these colonies. Adult workers retained most of the IGR throughout the experimental period. Larvae had an increase in radiolabel through the first 36 hours of exposure and then a decline throughout the remaining time. Pupae, queen, and egg stages received only traces of the IGR. The biological half-life of the IGR in these colonies never exceeded 2 days. Treatment of colonies with different amounts of brood relative to adult ants indicates that whenever this ratio is low, greater amounts of the IGR are found associated with the immature stages. Experiments designed to study the distribution of an IGR within an individual ant revealed that through 11 days over half the radiolabel remained in the crop of the adult ant. After 4 days, this radioactivity consisted primarily of metabolic breakdown products of the parent compound. Topical treatment of last instar sexual larvae with R-20458 and R0-10-3108 indicates that the latter remained on the cuticular surface for longer periods of time. The increased persistence of R0-10-3108 on the cuticle permits it to be distributed to other members of the colony. Metabolism of this material by treated larvae was not as fast as was found with R-20458. Per os treatment of last instar sexual larvae shows that metabolism was not the same as with topical treatment. R0-3108 was metabolized more rapidly than R-20458 by this route of IGR administration. Excretion of metabolic compounds in this treatment was virtual non-existent. Attempts to improve distribution of an IGR to the queen and immature stages using various formulations were not successful.