Interspecific competition between Fopius arisanus and Psyttalia incisi (Hymenoptera: Braconidae), parasitoids of Bactrocera dorsalis (Diptera: Tephritidae)

Fopius arisanus (Sonan) and Psyttalia incisi (Silvestri) are two important solitary endoparasitoids of Bactrocera dorsalis (Hendel). This study investigated the interspecific competition between these two parasitoids in the oriental fruit fly and the parasitic effect of P. incisi on hosts that have previously been parasitized by F. arisanus. The results showed that P. incisi did not discriminate against hosts that had been parasitized by F. arisanus at the egg stage. The parasitism percentage by P. incisi was lower on hosts previously parasitized by F. arisanus (75.3%) than on non-parasitized hosts (83.3%). Successive parasitization by F. arisanus and P. incisi resulted in the mass mortality of host larvae and pupae, with the death of 50.8% of the host pupae. The dissection of multiparasitized hosts showed that F. arisanus was the dominant parasitoid of host larvae; the higher mortality in the supernumerary P. incisi was due to physiological inhibition by the pioneer. The results further indicated that F. arisanus won almost all competitions against P. incisi, as demonstrated by the finding that F. arisanus emerged more often than P. incisi from multiparasitized hosts. The total emergence of parasitoids (76.5%) from the treatment in which the hosts were successively exposed to the two parasitoids was slightly higher than the emergence from the treatments in which the hosts were exposed to only one species (F. arisanus: 62.9%, P. incisi: 71.8%), which suggests that the combined application of these two parasitoids is a promising approach for biological control.