Document: ELI-3-51-12

Larval competition between two parasitoids in the California red scale system: Implications for coexistence and biological control.

BORER, E.T.*

University of California at Santa Barbara, Santa Barbara, CA ¹

Abstract:
A reanalysis of a published larval competition experiment between two parasitoids of California red scale (Aonidiella aurantii) suggests that the common entomological assumption that ectoparasitoids are intrinsically superior competitors against endoparasitoids may not always hold. An endoparasitoid in this system (Encarsia perniciosi) appears to gain competitive ability with increasing larval age. Unfortunately the published data cover only the first 105 degree-days of Encarsia development, rather than the approximately 375 degree-days required to complete larval development. I performed a lab experiment to investigate the outcome of the competitive interaction between Aphytis melinus (ectoparasitoid) and Encarsia throughout the endoparasitoid's larval development. When Encarsia parasitized first instar hosts, Aphytis had a decreased probability of competitive success with increasing Encarsia larval development time. However, in second instar hosts, Aphytis has a decreasing probability of emergence through time, regardless of Encarsia presence; Aphytis lost only a slight numerical advantage in hosts containing Encarsia, regardless of the endoparasitoid's larval age. In contrast, in both first and second instar hosts, as Encarsia larvae aged, they steadily increased their probability for success against their ectoparasitoid competitor. These results suggest a possible mechanism for competitive coexistence among two species with strongly overlapping resource requirements and have implications for biological control.

Keywords: larval competition, hyperparasitism, endoparasitoid, ectoparasitoid

This abstract is being presented at: 2:00 PM in session:
Oral Session #15: Parasitoids and Diseases.