Photoperiod controls insulin and juvenile hormone signaling pathways via the circadian clock in the bean bug Riptortus pedestris (Hemiptera: Alydidae)

Abstract

Most multivoltine insects in temperate zones enter diapause in response to short days. The photoperiod is evaluated in these organisms by a photoperiodic time measurement system, which involves the circadian clock, and activates or inactivates endocrine organs or cells to alter their physiological status. Although the physiological mechanisms underlying insect photoperiodism have been extensively studied, the molecular linkage between the circadian clock and endocrine signaling pathways remains unclear. In this study, we evaluated the bean bug Riptortus pedestris (F.) (Hemiptera: Alydidae), which enters adult (reproductive) diapause in response to short days. A gene encoding the insulin-like peptide ILP1, which is expressed in the pars intercerebralis in the brain, was upregulated and involved in fecundity under long days. Ilp1 appeared to function independently of the photoperiodic response controlled by juvenile hormone signaling. Cyp15, which encodes an epoxidase crucial for juvenile hormone biosynthesis, was upregulated and involved in ovarian development under long days. RNA interference targeted against the circadian clock gene per canceled the Ilp1 and Cyp15 suppression and allowed females to be reproductive even under diapause-inducing short days. Thus, the circadian clock may control the photoperiodic response by altering the expression of key elements in two independent endocrine pathways.