Evaluation of the Predatory Efficacy of Arma chinensis Against Larvae of Helicoverpa armigera and Spodoptera exigua

[Objective] To determine the control potential of Arma chinensis against major soybean pests Helicoverpa armigera and Spodoptera exigua, thereby providing theoretical and practical support for biological pest control in soybean fields. [Methods] Laboratory and field experiments were conducted to assess the predation capacity, feeding preference, and field control effect of third~fifth-instar nymphs and male/female adults of A. chinensis on first, third and fifth-instar larvae of these two pests. Predation functional responses were fitted to analyze predation characteristics and the relationship between searching efficiency and prey density. [Results] Both nymphs and adults of A. chinensis preyed on the larvae of H. armigera and S. exigua, with the predation functional responses conforming to the Holling Type II disk equation, which presented the highest predatory efficiency. The female adult of A. chinensis showed strong predation capacity against H. armigera (55.368) and S. exigua (50.699) larvae, with the highest daily prey consumption of 13.158 and 13.699 individuals, respectively. Searching efficiency of A. chinensis was negatively correlated with prey density, and significantly higher for first-instar than third-instar larvae. Under cooccurrence conditions, A. chinensis displayed an obvious feeding preference for H. armigera larvae. Field trials demonstrated that female adults of A. chinensis generated a 70% population decline rate of H. armigera. Meanwhile, the population decline rate of S. exigua reached over 80%. Female adults of A. chinensis achieved field control rates of 80% against H. armigera larvae and 70% against S. exigua larvae. [Conclusions] A. chinensis has strong predation and control potential against the larvae of H. armigera and S. exigua. Among these, females of A. chinensis demonstrated the highest efficacy in controlling the two types of Lepidoptera larvae, both indoors and in field conditions. It is a promising biological control agent for soybean fields and provides a scientific basis for large-scale application.