【目的】 草地贪夜蛾Spodoptera frugiperda (J.E. Smith)和棉铃虫Helicoverpa armigera (Hübner)是玉米穗期的重要害虫，均具有自相残杀行为，且存在对食物及空间资源的竞争。研究草地贪夜蛾和棉铃虫种内和种间的攻击和防御行为，为明确二者田间条件下的种间关系提供参考。【方法】 在室内有食物条件下，设置草地贪夜蛾4-6龄幼虫和棉铃虫4-6龄幼虫15个龄期组合，观察竞争行为出现的频率，并记录20 min内草地贪夜蛾和棉铃虫攻击和防御行为的类型及次数；24 h后记录幼虫存活情况，并计算幼虫死亡率。【结果】 棉铃虫种内竞争主要表现为攻击行为，在5龄和6龄幼虫竞争时最明显，其中5龄幼虫头部接触行为和6龄幼虫猛击行为出现的频率最高，分别占各自竞争行为总数的46.1%±3.1%和51.0%±2.3%。草地贪夜蛾和棉铃虫种间竞争行为都主要表现为攻击行为，同龄期草地贪夜蛾与棉铃虫竞争时，4龄草地贪夜蛾猛击行为出现的频率显著高于棉铃虫，5龄棉铃虫头部接触行为出现的频率显著高于草地贪夜蛾，而6龄幼虫各行为出现频率均无显著差异。不同龄期的草地贪夜蛾和棉铃虫竞争时，6龄幼虫头部接触行为出现的频率显著高于5龄，同龄期竞争时草地贪夜蛾与棉铃虫的存活率无显著差异，草地贪夜蛾4-6龄幼虫的存活率依次为83.3%、86.6%、80.0%，棉铃虫4-6龄幼虫的存活率分别为76.7%、73.3%、63.3%。不同龄期幼虫竞争时，5龄草地贪夜蛾和5龄棉铃虫幼虫存活率分别为80.0%和56.7%，均显著低于6龄棉铃虫和6龄草地贪夜蛾幼虫存活率（100%）。【结论】 草地贪夜蛾和棉铃虫幼虫种间竞争激烈，同一龄期幼虫竞争时，草地贪夜蛾竞争优势不明显，而5龄和6龄幼虫竞争时，6龄草地贪夜蛾幼虫的竞争优势更明显。

 [Objectives]  To investigate intra and interspecific attack and defensive behaviors of the fall armyworm, Spodoptera frugiperda (J. E. Smith) and the corn earworm, Helicoverpa armigera (Hübner), important maize pests that engage in cannibalistic behavior and compete for food and habitat, and thereby further understanding of interspecific relationships between these species in the field. [Methods]  Under indoor food conditions, 15 instar combinations of 4-6 instar larvae of S. frugiperda and 4-6 instar larvae of H. armigera were set up, the frequency of competitive behavior was observed, and the types and times of attack and defense behaviors of S. frugiperda and H. armigera were recorded within 20 min. [Results]  Attack behavior was the predominant form of intraspecific competition in H. armigera, and was more obvious in competition between 5th and 6th instar larvae. The frequency of head touching in 5th instar larvae, and the frequency of strike behavior in 6th instar larvae, were the highest, accounting for 46.1% ± 3.1 % and 51.0% ± 2.3%, respectively, of all competitive behaviors. Both species displayed attack behavior during interspecific competition. The frequency of strike behavior was significantly higher, and recoil behavior significantly lower, in 4th instar S. frugiperda larvae than in 4th instar H. armigera larvae. The frequency of head touching was significantly higher, and the frequency of recoil and retreat behavior significantly lower, in H. armigera during competition between 5th instar S. frugiperda and 5th instar H. armigera larvae. There were no significant differences in the frequencies of competitive behaviors between 6th instar S. frugiperda and H. armigera larvae. The frequency of head touching was significantly higher in 6th instar larvae than in 5th instar larvae, but the frequency of recoil and retreat behavior was significantly lower, both for S. frugiperda and H. armigera. Fourth to 6th instar larvae of S. frugiperda had similar survival rates (83.3%, 86.6% and 80.0%, respectively) in competition with the same instar of H. armigera (76.7%, 73.3% and 63.3%, respectively). Survival of 5th instar S. frugiperda and H. armigera larvae was 80% and 56.7%, respectively, which is significantly lower than the survival of 6th instar larvae, which was 100% for both species. [Conclusion]  Interspecific competition between S. frugiperda and H. armigera can be intense. S. frugiperda had no obvious competitive advantage in competition with H. armigera larvae of the same instar, but 6th instar S. frugiperda larvae were competitively superior to 5th instar H. armigera larvae.