BIOLOGY AND PHYSIOLOGY OF THE WHITE MUTANT OF THE TOBACCO HORNWORM, MANDUCA-SEXTA (L)

A white mutant of the tobacco hornworm, Manduca sexta, was discovered among wild-type, blue-green larvae in a laboratory colony routinely su pplemented with field-collected insects. The mutant is pinkish-white w hen reared on artificial diet and maintains this coloration from egg h atch through pupation. Spectral analyses showed that the blue chromoph ore, biliverdin, which is present in the integument and plasma of wild -type, diet and tobacco-reared larvae, was lacking in the white mutant reared on the same diets. Insecticyanin levels determined by radial i mmunodiffusion in the integument and plasma of the white mutant were h alf that of normal blue-green larvae. The topical application of incre asing amounts of the juvenoid, 2-(1-methyl-2-(4-phenoxyphenoxy)ethoxy) p to wild-type, day 1 first stadium larvae of M. sexta was positively correlated with the intensity of white coloration, which first appeare d in newly molted second instars and was retained until pupation. Whit e-mutant larvae developed slower and were slightly larger than wild-ty pe larvae. The corpora allata from last stadium, day 0 larvae of the w hite mutant demonstrated a higher rate of JH/JH acid biosynthesis and the hemolymph had a higher titer of JH than the wild type of the same age. These studies suggested that JH may play a role in the regulation of the white phenotype. No differences were noted in the level of JH esterase activity between the two strains during the last stadium.