Early-acting competitive superiority in opiine parasitoids of fruit flies (Diptera: Tephritidae): Implications for biological control of invasive tephritid pests

Understanding and predicting potential competitive outcomes is critical in the design of biological control programs when considering multiple agent introductions. Tephritid fruit flies (Diptera: Tephritidae) include some of the most destructive pests of fruit and vegetable crops worldwide. Parasitoid guilds of fruit-infesting tephritids are dominated by opiines (Hymenoptera: Braconidae: Opiinae) that have been the main agents used for biological control of pest tephritids. All opiine parasitoids are solitary koinobiont endoparasitoids that attack host eggs or larvae and emerge as adults from host puparia. Thus, a host initially attacked by an egg-larval parasitoid can be subsequently attacked by a larval parasitoid, providing an ideal system to test the Earlyacting Competitive Superiority Hypothesis (i.e., the first species occupying a host or exploiting early host stages has an advantage over competitive species). We reviewed the literature on interspecific competition among opiine fruit fly parasitoids, which reveals strong evidence supporting the early-acting competitive superiority hypothesis by egg-larval over larval parasitoids, through physiological suppression mechanisms. Competitive outcomes among larval parasitoids, however, depend on early action as well as the morphological characteristics used in direct physical competition of their first instars (e.g., size of mandibles). We discuss the range of ecological mechanisms facilitating coexistence of interacting species and highlight the ecological consequences of interspecific competition as evidenced by historical competitive displacements of introduced opiine parasitoids for biocontrol of tephritids. Finally, we provide a framework for exploring the role of interspecific competition, among other factors, in selecting opiine parasitoids for biocontrol of invasive tephritids.