Biocontrol potential of the native parasitoid Cotesia gregalis (Hymenoptera: Braconidae) against the invasive fall webworm (Lepidoptera: Erebidae): Insights from reproductive biology and release strategies

BACKGROUND: The fall webworm, Hyphantria cunea (Drury) (Lepidoptera: Erebidae), is a global quarantine pest that poses a severe threat to forestry. In China, where the moth is invasive, biological control has relied largely on pupal parasitoids, whereas effective biocontrol agents targeting the damaging larval stage remain unavailable. Cotesia gregalis Yang et Wei (Hymenoptera: Braconidae) is a native parasitoid of fall webworm larvae in China. This study evaluated its biocontrol potential focusing on mass rearing and optimized field release strategies. RESULTS: C. gregalis exhibited high reproductive capacity (65 offspring/female) and efficient host utilization (27 offspring/host). Rapid development supported the feasibility of mass production, with a generation completed in just 13 days at 30 °C. The established thermal constant provided a predictive metric for synchronizing parasitoid release with pest occurrence. Nutritional status of the parasitoids determined operational longevity; carbohydrate supplementation extended female survival fivefold, highlighting the necessity of habitat management in release sites. Females exhibited a significant preference for fourth-instar and older host larvae. Field cage evaluation confirmed that releasing female adults at a 2:1 parasitoid-to-host ratio during the host's late fourth to fifth larval instars achieves an optimal balance between high control efficacy and sustainable parasitoid population buildup. CONCLUSION: This study indicates that C. gregalis may be an efficient biocontrol agent against H. cunea especially the management of the larval stage. It also facilitates the development of a full-life-cycle biological control strategy for this insect pest.