Integrin is a cell surface protein that is composed of α and β heterodimer and mediates cell interaction with extracellular matrix or other cells including microbial pathogens. A full length cDNA sequence (2,517 bp) of a integrin subunit β1 (HaITGβ1) was cloned from the oriental tobacco budworm, Helicoverpa assulta. Phylogenetic analysis showed that HaITGβ1 was clustered with other insect β integrin subunits with the highest amino acid sequence identity (61%) to β1 of other Noctuidae such as Spodoptera exigua and S. litura. Structural analysis of the HaITGβ1 possessed all functional domains known in other insect β1 integrins. RT-PCR analysis showed that HaITGβ1 was expressed in all developmental stages and all tested tissues of H. assulta. Injection of double-stranded HaITGβ1 RNA (dsHaITGβ1) into third instar of H. assulta suppressed HaITGβ1 expression and resulted in significant delay from last larval stage to pupal stage. The dsHaITGβ1 injection significantly impaired nodule formation of H. assulta in response to bacterial challenge and hemocyte adherence. These results suggest that HaITGβ1 plays crucial roles in cellular immune responses as well as development in H. assulta.