Understanding predator–prey and predator–predator interactions is essential for evaluating the effectiveness of biocontrol agents and developing efficient pest management strategies. This study investigates the effects of prey species, predator life stage, and predator density on the predatory efficiency of the generalist predator Rhynocoris fuscipes (Fabricius) under semi-field conditions. Both the nymphs and adults of R. fuscipes consumed significantly more second-instar larvae of S. frugiperda than larvae of S. litura or M. separata. Notably, fifth-instar nymphs and adults exhibited higher predation capacity (11.75 ± 0.37 and 10.90 ± 0.40 larvae) than fourth-instar nymphs (9.05 ± 0.29 larvae) on S. frugiperda. R. fuscipes demonstrated a Type II functional response at all developmental stages toward each prey species, and fifth-instar nymphs revealed higher attack rates (a = 1.5205 ± 0.0544) on S. frugiperda; additionally, the handling time did not significantly differ among three prey species. It suggests that this predator may be more effective at controlling noctuid populations at low prey densities. As predator age and density increased, intraspecific competition among R. fuscipes also intensified. In a multi-prey system, R. fuscipes showed a marked preference for S. frugiperda over the other two prey species. These findings indicate that the fifth-instar nymphs and adults of R. fuscipes are particularly effective in suppressing early-instar larvae of the three noctuid pests, especially S. frugiperda, at low densities. This study enhances our understanding of the predation capacity and prey preference of R. fuscipes towards the three noctuid pests and provides a foundation for the development of more targeted and efficient pest management strategies using this predator.

In integrated pest management (IPM), achieving a balance between biological and chemical control strategies is essential for effective pest control. Therefore, it is crucial to assess the impact of chemical pesticides on natural enemies. Neonicotinoid insecticides, particularly dinotefuran, are among the most widely used insecticides globally. This study investigated the acute toxicity of dinotefuran to adult predatory natural enemy Picromerus lewisi and evaluated its effects on offspring growth and predation. The results showed that the 72 h median lethal concentrations (LC₅₀) of dinotefuran for female and male adults (F₀) were 0.624 mg/L and 0.592 mg/L, respectively. Exposure to LC₅₀ concentrations of dinotefuran significantly reduced parental fecundity, longevity, and offspring growth and predatory ability. The most pronounced effects were observed when both female and male adults were exposed. Specifically, the pre-oviposition period was 2.64 times longer than in the control group, oviposition frequency dropped to 18.6%, total fecundity decreased to 13.4%, and the offspring emergence rate was reduced to 50% of the control group’s level. Furthermore, predation efficacy of F₁ generation (5th instar nymphs and adults) on Spodoptera exigua and Spodoptera litura larvae reduced by 52.76% to 66.81%. Exposure of only female adults also led to significant but less severe effects on offspring, while male-only exposure showed the least impact. These findings highlighted the toxicological risks of dinotefuran to P. lewisi, impairing both reproductive and predatory functions, which could undermine biological control and affect the success of IPM strategies.