Title:[The "presence" of an alien species changed mutual interference between native parasitoid females.]

Three-species systems allow an understanding of irregular, complex population dynamics of multiple species assemblages, with emerging effects of indirect interactions. We focused on a laboratory system consisting of a bruchine species Callosobruchus chinensis as a host and two parasitoids, a chalcid Anisopteromalus calandrae and a braconid Heterospilus prosopidis, with each species introduced sequentially.

With a parameterized semi-mechanistic model, previous study found the introduction of a second parasitoid (H. prosopidis) destabilized the dynamics of host-parasitoid (A. calandrae) interaction towards chaos (Tuda and Shimada 2005). Comparison of parameters before and after the introduction indicated that the parameter that was altered by the introduction was solely the mutual interference in A. calandrae, which decreased by introduction of H. prosopidis females.

To confirm the parameter change detected at the population level, we observed an interference behavior between A. calandrae females with a H. prosopidis female when parasitizing their common host using CCD video camera. The results obtained show that A. calandrae females increase their tendency to leave the patch when a H. prosopidis female was introduced.