The introduction of the fall armyworm, Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae), into Thailand has significantly altered the dynamics of maize pests. It has overshadowed Ostrinia furnacalis (Guenée) (Asian corn borer) (Lepidoptera: Crambidae), previously the most severe maize insect in Thailand. This transition is postulated to stem from the superior intraguild predation (IGP) capabilities of S. frugiperda. To validate this supposition, we assessed the co-distribution patterns and damage locales of both pests within maize fields and analyzed the IGP's repercussions on their larval growth, survival, and fecundity. Our findings demonstrate that: (i) incidence of O. furnacalis in maize fields is markedly reduced following the introduction of S. frugiperda; (ii) abundance of S. frugiperda and O. furnacalis is negatively correlated in field; (iii) interspecific interactions affect the spatial distributions of S. frugiperda and O. furnacalis on shared plants; (iv) S. frugiperda has lower generation time and higher fecundity; and (v) IGP amplifies the growth rate of S. frugiperda and elevates mortality in O. furnacalis. Moreover, in response to the competitive pressure exerted by S. frugiperda, O. furnacalis exhibited expedited molting and growth without a commensurate increase in size. Our data suggest IGP proficiency underpins S. frugiperda's dominance inThai maize fields. We propose a niche differentiation on spatiotemporal distribution facilitating the coexistence of S. frugiperda and O. furnacalis. The impact of S. frugiperda on pest management strategies is discussed.