Extrinsic and Intrinsic Competition between Chouioa cunea Yang and Tetrastichus septentrionalis (Hymenoptera: Eulophidae), Two Pupal Parasitoids of the Fall Webworm, Hyphantria cunea (Lepidoptera: Erebidae)

The endoparasitoids <i>Chouioa cunea</i> Yang and <i>Tetrastichus septentrionalis</i> Yang (Hymenoptera: Eulophidae) are both gregarious pupal parasitoids of the fall webworm, <i>Hyphantria cunea</i> (Drury) (Lepidoptera: Erebidae). In order to analyze the competitive interactions between both parasitoids exploiting <i>H. cunea</i>, we assessed both extrinsic and intrinsic competition. The search time, oviposition duration, and oviposition frequency were used as evaluation criteria for extrinsic competition. The number of survival days, female ratio, and number of parasitoids emerging from the host were used as evaluation criteria for intrinsic competition. The results indicated that both parasitoid species were able to parasitize hosts that were already parasitized by competitors. The first released species consistently emerged as the superior competitor in multiparasitized hosts. Both parasitoid release orders and time intervals between oviposition affect the competition of parasitoids and the parasitic efficiency. The results emphasize the parasitic abilities of both parasitoid species and provide a basis for future research on competition mechanisms and biological control of <i>H. cunea</i>.