Enhancing natural enemy performance through plant secondary metabolites: The role of caffeine for the parasitoid Snellenius manilae

The food resources in the field can effectively strengthen the ability of natural enemies to control the pest. Certain compounds, in addition to carbohydrates and amino acids, may improve the physiological performance of insects. Caffeine, for instance, has been shown to enhance pollinator memory and physiological reactions. However, little is known about how caffeine influences parasitoids. The control effectiveness and survival rate of the parasitoid (Snellenius manilae) were tested in this study after the parasitoids were fed solutions with different concentrations of caffeine. We examined caffeine concentrations of 10⁻², 10⁻⁴, and 10⁻⁶ (M) mixed with a 25% sucrose solution and a pure sucrose solution as a control group. The results show that a concentration of 10⁻⁶ caffeine solution significantly increased the parasitism rate of S. manilae by 10.76% when compared to the control group. Despite the significantly lower survival rate and male bias of S. manilae offspring in the 10⁻² treatment, no further negative responses in growth performance, development time, or cocoon weight were observed. These findings suggest that an appropriate concentration of caffeine solution can have a positive impact on the control effectiveness of parasitoids in the laboratory. Our results highlight the potential of secondary compounds to increase the bio-control effectiveness. However, confirming the implications of these findings requires further field experiments.