Inter-specific competition and competition-free space in the tephritid parasitoids Utetes anastrephae and Doryctobracon areolatus (Hymenoptera: Braconidae: Opiinae)

Abstract

Utetes anastrephae (Viereck) and Doryctobracon areolatus (Szépligeti) are common, native, Neotropical braconid parasitoids of tephritid fruit flies that are sympatric and often found attacking the same host. The coexistence of the two species may be due in part to the longer ovipositor of D. areolatus that permits it to attack larvae in larger fruit than can U. anastrephae. This increases its potential host range and provides 'competitor-free space'. The capacity of U. anastrephae to persist in smaller fruit, exploitable by D. areolatus, suggested that it was a superior competitor in multiparasitised hosts. As predicted U. anastrephae had a competitive advantage over D. areolatus and this advantage occurred regardless of the order in which the two parasitoids attacked. Although we could not identify the precise mechanisms used for elimination of competitors, a possible cause is suggested by the formidable mandibles of the first-instar U. anastrephae. However, D. areolatus survival increased significantly if eggs had been deposited 24h prior to exposure to U. anastrephae. Older D. areolatus larvae might be more competitive after a period of development. Utetes anastrephae females were less likely to oviposit into hosts previously attacked by D. areolatus than vice versa. This was a second case of the relatively rare phenomenon of inter-specific discrimination of a previously exploited host within the opiine braconid parasitoids of frugivorous tephritids.