Juvenile hormone-III biosynthesis in presumptive long-winged and short-winged Gryllus rubens: Implications for the endocrine regulation of wing dimorphism

Abstract

In vitro rates of juvenile hormone-III biosynthesis were quantified for corpora allata from nascent long-winged and short-winged Gryllus rubens. Rates were measured during the penultimate and last stadia, two juvenile-hormone-sensitive periods of wing morph determination. This was done to assess the contribution of differences in rates of hormone biosynthesis to juvenile-hormone-mediated morph determination. Corpora allata from individuals of the same morph, sex and stage of development exhibited low variability in juvenile hormone-III biosynthetic rates. Developmental profiles of these biosynthetic rates for each sex and morph were U-shaped during each stadium. Rates varied from 1 to 5 and 0 to 5 pmol juvenile hormone-III/h/pair corpora allata during the penultimate and last stadium, respectively. Juvenile hormone-III biosynthetic rates did not differ significantly between morphs of the same sex on any day in development, except for a few cases at the beginning or end of each stadium. In general, developmental patterns of juvenile hormone-III biosynthesis were similar between the sexes of each morph. These data (1) provide no evidence that morph-specific differences in rates of juvenile hormone-III biosynthesis underlie juvenile-hormone-mediated morph determination, and (2) further implicate previously documented variation in juvenile hormone esterase activity in morph determination. Data on juvenile hormone biosynthesis, degradation and titre also collectively implicate cessation of biosynthesis rather than elevation of juvenile hormone esterase activity in producing the steep decline in the juvenile hormone titre early in the last stadium; this decline presumably initiates metamorphosis. Alternate morph development appears to result at least in part from differential clearance of low levels of juvenile hormone following the steep decline.