Sexual dimorphism of diapause regulation in the hemipteran bug Pyrrhocoris apterus

Abstract

Diapause is one of the major strategies for insects to prepare for and survive harsh seasons. In females, the absence of juvenile hormone (JH) is a hallmark of adult reproductive diapause, a developmental arrest, which is much less characterized in males. Here we show that juvenile hormone III skipped bisepoxide (JHSB₃) titers in hemolymph remarkably differ between reproductive males and females of the linden bug Pyrrhocoris apterus, whereas no JH was detected in diapausing adults of both sexes. Like in females, ectopic application of JH mimic effectively terminated male diapause through the canonical JH receptor components, Methoprene-tolerant and Taiman. In contrast to females, long photoperiod induced reproduction even in males with silenced JH reception or in males with removed corpus allatum (CA), the JH-producing gland. JHSB₃ was detected in the accessory glands (MAG) of reproductive males, unexpectedly, even in males without CA. If there is a source of JHSB₃ outside CA or a long-term storage of JHSB₃ in MAGs remains to be elucidated. These sex-related idiosyncrasies are further manifested in different dynamics of diapause termination in P. apterus by low temperature. We would like to propose that this sexual dimorphism of diapause regulation might be explained by the different reproductive costs for each sex.

Keywords: Allatectomy; Corpus allatum; Juvenile hormone; Mating; Methoprene-tolerant; Photoperiod; Reproductive diapause; Seasonality; Taiman.