Ultrabithorax regulates Leptinotarsa decemlineata wing development along with insulin and ecdysteroid signaling pathways

Leptinotarsa decemlineata (Say) (Colorado potato beetle, CPB) is a notorious pest of potatoes. Its hardened forewings, known as elytra, protect the hindwings and the abdomen against enemies and chemical pesticides. Ubx plays a crucial role in differentiating insect wings, but the molecular mechanism remains unclear. Our research showed that Ubx is highly expressed in the T3 thoracic segment (T3) and appendages, while Ubx is absent in the forewings. RNA interference for Ubx resulted in the dorsal plate of the T3 being shifted toward the T2, hindwings were sheathed from the membranous in adults, and forewings were curling. The hindwing development-related genes downstream of Ubx, including LdDpp, LdIro, LdVg, LdWg, and LdASH, were significantly up-regulated in Ubx-inhibited insects compared with the control, by 2.40, 1.88, 1.81, 1.89, and 2.81 times, respectively. After feeding 20-hydrosyecdysone (20E), the forewing was flatter and more stretched than the control, leading to increased wing area, which indicates Ubx regulation is associated with the feedback of ecdysteroids. The expression levels of 3 ecdysteroid receptor genes EcR, EcRA, and EcRB were significantly lower in knocking down LdUbx insects than the control and was able to be recovered by 20E feeding, suggesting that ecdysteroid is associated with LdUbx-regulated wing development. Cosilencing LdUbx and LdAkt genes significantly inhibited the growth of forewings and hindwings, reducing the area of the wings. Together, our findings suggested that LdUbx regulates wing development along with ecdysteroid and insulin-like peptide signaling pathways, which provides a novel molecular mechanism of wing development and differentiation in insects.