Interactions between Chelonus oculator and Se NPV in the biological control of Spodoptera exigua at different larval stages

The beet armyworm, Spodoptera exigua Hübner, is a destructive pest of many vegetable and field crops, and its management has become increasingly difficult due to widespread insecticide resistance. Biological control is therefore a critical component of sustainable pest management. Two important natural enemies of S. exigua are the egg–larval parasitoid Chelonus oculator and the S. exigua nucleopolyhedrovirus (SeNPV); however, their combined use requires an understanding of how viral infection affects parasitoid performance. This study evaluated the interactions between C. oculator and SeNPV across second, third, and fourth instar larvae of S. exigua under laboratory conditions. Larvae were exposed to parasitism alone, SeNPV alone (10 4 –10 8 OBs⋅mL −1 ), or parasitism followed by viral infection. SeNPV caused dose-dependent increases in larval mortality, with concentrations of 10 7 –10 8 OBs⋅mL −1 achieving nearly 100 % mortality within 7–11 days. When parasitism and viral infection were combined, mortality increased more rapidly at high viral doses; however, parasitoid development was strongly inhibited. No wasps emerged from hosts infected with 10 7 –10 8 OBs⋅mL −1 , and emergence declined sharply even at moderate viral concentrations. These results demonstrate that although SeNPV enhances short-term host mortality, it can severely reduce parasitoid survival, creating potential antagonism between these biocontrol agents. Effective integration of C. oculator and SeNPV will therefore require careful optimization of viral dose and application timing to balance immediate pest suppression with long-term parasitoid conservation.