An Integrated Morphometric-Molecular Framework for Characterization of Developmental Stages in the Safflower Aphid Uroleucon gobonis (Matsumura)

Reliable identification of pest developmental stages provides a foundation for investigating aphid development and adaptive mechanisms and informs the selection of timely interventions in integrated pest management. In this study, eight morphological indicators of Uroleucon gobonis were distinguishing under a stereomicroscope. Additionally, six candidate genes identified from transcriptomic data were selected to characterize their expression profiles across five developmental instars. These results showed that the body length enabled distinguishing of the aphids from the first instar to the fourth instar, while antennal length and cauda length facilitated distinction between the second–fourth instar nymphs; cornicle length allowed separation of the third instar and subsequent instars. In contrast, body width permitted discrimination primarily between the first and second instars; head width, foreleg length, and hindleg length exhibited substantial overlap across instars, limiting their utility for instar discrimination. Elevated expression of DN1031, DN1019, and DN1093 was a prominent feature of first instar nymphs. DN1098 was persistently increased from the first to the third instar, which facilitated discrimination among these three developmental stages. The fourth instar was characterized by the concurrent down-regulation of DN1098 and DN1031 relative to the third instar, whereas adults exhibited a distinct expression peak of DN136 compared to other developmental stages. This study establishes an integrated instar-identification system for U. gobonis, combining rapid morphological screening with molecular characterization. This framework provides a valuable methodological basis for investigating developmental plasticity and supports the development of targeted pest management strategies.