Notch and Delta Control the Switch and Formation of Camouflage Patterns in Caterpillars

In most Papilio species, a younger larva mimics bird droppings but changes its pattern to match host plant colors in its final instar. This change is determined by juvenile hormone (JH) during the JH-sensitive period (JHSP) early in the fourth instar. Recently, we found that homeobox genes control the pre-pattern formation specifically during JHSP, but the molecular mechanisms underlying final patterning and pigmentation at molt are unknown. By knockdown of Delta and Notch in Papilio xuthus larvae, we here showed that these genes define the edge and pigmentation area in final patterns, during and even after JHSP, suggesting that they bridge the JHSP and molt. Knockdown of Delta in Papilio machaon led to similar phenotypic changes, and knockdown of Notch caused pigmentation loss in twin spots of the silkworm Multilunar (L) mutant. Our findings suggest the importance of the Notch signaling pathway in caterpillars' adaptive evolution of color pattern formation.