0023-6152

AA00697606

1467634

Unrefereed

0023-6152

AA00697606

Whether introduction of multiple natural enemies is more effective to suppress agricultural pests than that of a single enemy is one of the important questions for biological control. Intra–guild predation (IGP) among natural enemies has often been considered as a candidate to explain failure of biological control by multiple enemies. Classical theoretical studies on IGP supported the view, whereas some empirical studies did not. Since the classical models were very simple, neglect of adaptive behavior of pests and natural enemies might be a reason for the partial discrepancy between the theory and observation. In a companion paper, we considered two kinds of predator–specific adaptive defenses by the pest in an IGP system and revealed their possible effects on biological control by multiple natural enemies. In the present paper, we examined the effects of predator–nonspecific adaptive defense on success or failure of biological control by multiple natural enemies. Although the predator–nonspecific defense enhanced three species coexistence as the predator–specific defense did, introduction of two natural enemies could rarely improve the efficiency of biological control. We found that the specificity of the defense against two predators and the trade–off between allocation of effort toward two kinds of defenses were key factors to realize more efficient suppression of the pest by multiple natural enemies. Our results suggest that considering plasticity in behavior of pests and natural enemies may be essential to evaluate and predict efficiencies of biological control.