Diet-mediated egg quality in Corcyra cephalonica predicts Trichogramma performance: implications for biocontrol production

Despite extensive optimisation of larval diets for mass-rearing the factitious host Corcyra cephalonica, the biochemical mechanisms linking host nutrition to Trichogramma parasitoid performance remain poorly understood. This study evaluated diet-mediated variation in host egg biochemical quality by quantifying total protein, sugars, free amino acids (FAA), DNA, and RNA across ten cereal-based diet formulations and relating these parameters to parasitisation and emergence of T. chilonis and T. japonicum. Eggs produced on the bajra + sorghum supplemented diet exhibited the highest biochemical enrichment across all measured constituents, increasing by 159 –1,150% over broken rice controls. These eggs supported significantly greater parasitisation (≈79%) and adult emergence (>82%) in both parasitoid species. Egg protein (r = 0.94) and FAA content (r = 0.91) were strong predictors of parasitoid performance, identifying reliable biochemical indicators of host suitability. Parasitisation significantly increased host egg biochemical constituents with species-specific patterns consistent with differential resource utilisation strategies. Dietary fat content emerged as the strongest predictor of egg biochemical richness (r = 0.750–0.811), followed by dietary protein (r = 0.638–0.670). These findings establish practical biochemical benchmarks for host quality assessment (protein >6 mg g−¹; FAA >45 mg g−¹) and provide actionable guidance for optimising Trichogramma mass-production systems used in biological control programmes.