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The larvae exhibit a color polymorphism first described by Edwards in 1893. Nigra larvae are solid black, bicolor is black with a mid dorsal orange band, and rufa are solid orange to rust colored (although there can be a fair amount of melanic coloration between body segments, especially in the lower instars).  The larvae are leaf skeletonizers, and large stands of wild sunflower can be entirely skeletonized, i.e., denuded, due to population explosions occurring later in the year, usually September. There are five larval instars.  The larvae feed gregariously, primarily as sibships, during the first four instar. This gregarious behavior confers greater protection from parasitism. At the last instar, the fifth instar, the larvae wonder and feed individually. Third and fourth instar larvae enter diapause at the onset of winter.  The season can end with a huge larval population, but from personal observation few survive to start the next season. As a result, populations annually go through bottlenecks which may have some evolutionary significance.
 
 

The nigra phenotype. The image contains one bicolor with a reduced orange mid dorsal band.

The rufa phenotype. Also present are some bicolors.

 

The bicolor phenotype. Fifth instar larva.

The rufa phenotype. Fifth instar larva. Note variable melanization that can occur between body segments

The pupae are variable in the extent of melanization ranging from one nearly devoid of black markings to one almost blackened by them.  There also appears to be a non sex linked hemolymphic polymorphism.  Two discrete forms exist, a creamy white vs. a pale yellow background coloration.  However, there appears to be some linkage between the hemolymphic morphs and the degree of melanization because heavily marked pupae are never yellow, and, alternatively, those nearly devoid of markings are never white.
 
 

The pupal stage showing some of the dark marking variability.

I initiated studies in 1966 to determine the genetic mechanism underlying the larval polymorphism as part of my M.S. degree thesis at Arizona State University.  Surprisingly, up to this time very little scientific work of this nature had been done.  I solved the genetic mechanism in 1967, and two years later published the results in Genetical Research ('The Genetics of Three Polymorphic Larval Colour Forms of Chlosyne lacinia'. Genetical Research, 1969. Vol 14: pp. 333-336. Page 333, Page 334, Page 335, Page336).

My research showed the mechanism to be an autosomal non-linked, two locus epistatic system.  The bicolor and nigra determining alleles are at one locus, and the rufa determining alleles at another locus of a non-homologous chromosome.  Bicolor and rufa are determined by dominant alleles, and the dominant rufa allele is epistatic over the bicolor locus, i.e., the bicolor and nigra phenotypes are surpressed when the dominant rufa allele is present on the other chromosome.  When Raymond Neck, Guy Bush, and Boyce Drummond learned of the mechanism from my work, they extended this research further, and in 1971 published results indicating the existence of lethals closely linked to the dominant rufa allele.
 

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