Equivalence of riboflavin-binding hexamerin and arylphorin as reserves for adult development in two saturniid moths.

The riboflavin-binding hexamerin (RbH) and arylphorin (ArH) were compared as storage reservoirs for adult development in Hyalophora cecropia. The two hexamerins were metabolically labeled with [3H]leucine and [35S]methionine, isolated by column chromatography, and separately injected into pupae whose diapause had been terminated by chilling. By the time of eclosion at least 98% of both hexamerins had been cleared from the hemolymph. Every reproductive and somatic tissue tested contained trichloroacetic acid-precipitable label; consistent differences between the two hexamerins were not detected in the distribution of their label to these tissues. While incorporation of intact hexamerins was not ruled out, hydrolysis and reincorporation of the liberated amino acids were indicated by label in vitellogenin and lipophorin, and by differences in 35S/3H ratios, which ranged from over 1.0 in chorions to 0.4 in wings, as compared with 0.75 in the injected hexamerins. Injection of [35S,3H]RbH from H. cecropia into A. luna, a species in the same subfamily whose pupae lack this hexamerin, resulted in a pattern of isotope incorporation similar to that yielded by RbH in the donor species. In neither species was there indication of a developing adult tissue that distinguished between RbH and ArH as precursor reservoirs for morphogenesis. This equivalence helps explain how many species of Lepidoptera are able to complete metamorphosis and reproduce without expressing an RbH gene. Evidence is also presented that ArH stored in the fat body protein granules during pupation may be utilized differently from that remaining in pupal hemolymph.