Hormonal control of seasonal-morph determination in the small copper butterfly, Lycaena phlaeas daimio Seitz.

Abstract

Spring and summer morphs of Lycaena phlaeas daimio Seitz. are characterized by a wing colour of red and reddish brown, respectively. When newly ecdysed pupae destined to be summer or intermediate morphs (90 or 10%) by larval exposure to long days (long-day pupae) were decapitated or decerebrated, more than half of the operated pupae developed into intermediate and spring morphs (48 and 7%). But, in pupae destined to be spring, intermediate, or summer morphs (72, 22 or 4%) (short-day pupae) these operations did not produce any significant changes in the seasonal morph. Brains excised from newly ecdysed long-day pupae were transplanted into the abdomen of decapitated short-day pupae of the same age. The implants changed most recipients into summer and intermediate morphs (46 and 36%). However, when the brains of short-day pupae were used, no significant changes occurred in the seasonal morph. When long-day or short-day pupae were treated with 20-hydroxyecdysone just after pupation, they produced more reddish wings than those of the untreated or saline-treated controls. When the application was followed by chilling, already known to induce the reddish morph, the effects of both treatments are cumulative so that more reddish adults developed. The results indicate that the brain of long-day pupae secretes a factor causing the wing to be brownish. In the absence (or low titre) of the factor, most short-day pupae develop into spring or intermediate morphs. Furthermore, ecdysteroids make the wing more reddish, when applied to newly ecdysed pupae.