Strategic Timing of Larval Harvest as a Practical Approach to Increase Baculovirus Mass Production

Baculoviruses are important bioinsecticides in integrated pest management, with in vivo production systems still predominant due to cost-effectiveness and scalability. However, inconsistencies in quality, such as viral infectivity and contamination, and polyhedra yield restrict their wider adoption. This study evaluated the infection dynamics of Spodoptera frugiperda multiple nucleopolyhedrovirus - Alphabaculovirus spofrugiperdae isolate 6 (SfMNPV6) in Spodoptera frugiperda larvae to determine the optimal harvest time for maximizing occlusion body (OB) yield. Larvae were exposed to three inoculum concentrations (1 × 10⁵, 1 × 10⁶, and 1 × 10⁷ OB/mL) and monitored daily from the third to the tenth day post-infection. We assessed larval survival, tegument color as an indicator of infection symptoms, and polyhedra yield. Results indicated dose-dependent variations in disease progression, with the infection peak occurring on days seven, eight, and ten for the highest to lowest inoculum concentrations, respectively. Pinkish tegument symptom was strongly correlated with maximum OB yield, making it a reliable visual indicator for harvest timing. Statistical modeling confirmed the relationship between tegument color and OB concentration, with pinkish larvae (symptomatic) significantly outperforming green (early infection stage) and gray (post-mortem period) larvae in virus production. This symptom-based monitoring provides a low-cost, non-invasive alternative to enhance timing in baculovirus harvest protocols. These findings suggest that optimizing harvest based on larval symptoms and dose-dependent infection dynamics can improve virus yield and product quality. This approach enhances the reliability of baculovirus-based bioinsecticides, providing a more effective production strategy to meet the increasing demand for biological control agents in sustainable agriculture, particularly as global pest pressures are intensified by climate change.