Interspecific competition between two ectoparasitoids of Phyllocnistis citrella (Lepidoptera: Gracillariidae): Cirrospilus brevis and the exotic Quadrastichus sp. (Hymenoptera: Eulophidae)

The eulophid Quadrastichus sp. was released in Spain in 1996 and 1997 to control the recently introduced citrus leafminer, Phyllocnistis citrella Stainton. Although this parasitoid became established, it did not exert any substantial control of P. citrella compared to the native Cirrospilus brevis Zhu, LaSalle and Huang which clearly predominated. To critically evaluate the results of the classical biological control program developed against P. citrella in Spain, we decided to test whether the observed field results concerning the exotic parasitoid Quadrastichus sp. and the indigenous C. brevis could have been forecasted from laboratory assays. An assay focusing on competition between Quadrastichus sp. and C. brevis was executed. The results obtained indicated that Quadrastichus sp. was an intrinsically superior competitor compared to C. brevis, the latter species becoming extinct in the laboratory competition trial. Environmental factors, not present in the conducted laboratory study, probably account for the outcome in the field. Although our laboratory results could be considered misleading, more post-colonization studies are warranted in classical biological control programs and, in any case, pre-introduction studies should still be conducted.