Functional characterization of the corazonin-encoding gene in phase polyphenism of the migratory locust, Locusta migratoria (Orthoptera: Acrididae)

Abstract

Locusts exhibit phase polyphenism in which phase transition between the solitarious (isolation-reared) and gregarious (crowd-reared) phenotypes occurs in response to crowding conditions. Phase transformation from solitarious to gregarious nymphs is accompanied by darkening of the body color and changes in classical morphometric ratios such as F/C (F hind femur length; C maximum head width). These changes occur in the absence of crowding if solitarious locusts are injected with the neuropeptide, corazonin (Crz). This study investigated the effects of the knockdown of the CRZ gene on body color and morphometric characteristics in the migratory locust Locusta migratoria (L.) (Orthoptera: Acrididae). An injection of dsRNA for Crz significantly reduced CRZ mRNA levels and reduced the intensity of darkening on the pronotum in nymphs. The silencing of CRZ expression in gregarious nymphs shifted the F/C toward a value typical of the solitarious form in the adult stage. However, the expression profiles of CRZ were similar between the gregarious and solitarious nymphs. Therefore, we conclude that Crz is responsible for phase-dependent changes in darkening and the morphometric ratio; however, these changes are not controlled through differential CRZ expression at the transcriptional level.