Single and Multiple Infestation by Coccoid Pests in Coffee Shape Plant Chemical Defenses and Interactions Across Trophic Levels.

Crop plants are attacked by multiple pests, inducing metabolic changes that shape interactions across trophic levels and influence the effectiveness of biological control. We examined how infestation by the coccoids Coccus viridis (scales) and Planococcus citri (mealybugs) modulates phytohormones, secondary metabolites, herbivore infestation, and behavior of the predator Cryptolaemus montrouzieri in Coffea arabica plants. Infestation by either scales or mealybugs activated the salicylate pathway but differentially regulated jasmonates and selected secondary metabolites. Scale infestation reduced mealybug performance, coinciding with elevated theophylline levels, whereas mealybugs activated jasmonates and upregulated several metabolites, including caffeine and catechin. The ladybug consumed coccoid pests and preferred mealybugs, but did not discriminate between scale- or mealybug-infested plant volatiles, suggesting limited specificity of herbivore-induced volatile blends in guiding predator foraging. Multiple infestation disrupted volatile-mediated attraction of the female ladybug. Our findings reveal the complexity of plant responses under multiple infestation and highlight species-specific interactions shaping tritrophic dynamics.