Trait-mediated indirect interactions commonly exist in food webs and can positively or negatively affect species competition, predation rate and parasitization rate, to name a few.  They can also affect the structure of biological communities.  In a coffee agroecosystem in the Soconusco region in Chiapas, Mexico, it has been demonstrated that the presence of Pseudacteon sp. (Diptera: Phoridae) inflicting its host Azteca instabilis (Hymenoptera: Formicidae) can increase the predation rate of Azya orbigera (Coleoptera: Coccinellidae) on the green coffee scale (Coccus viridis, Hemiptera: Coccidae), the mutualistic partner of A. instabilis.  Furthermore, in lab experiments, it has been found that the patrolling activity of A. instabilis on coffee bushes can by-protect the larvae of A. orbigera by scaring away their parasitoids.  In this study, we wanted to (1) further prove that the positive indirect effect of A. instabilis on A. orbigera exists in the field, and (2) test if the presence of Pseudacteon can result in an increase of the parasitization rate of A. orbigera. In the first test, we surveyed the pupae of A. orbigera in a 30 X 40 M² plot in a coffee plantation and calculated their corresponding distances to the closest Azteca nests, noting whether they were parasitized or not.  We performed the second test in insect rearing cages.  Two treatments were used: (1) cages contained A. orbigera, A. instabilis and parasitoids of A. orbigera; (2) cages contained A. orbigera, A. instabilis, parasitoids of A. orbigera and Pseudacteon sp.

Results/Conclusions

The result of the first test shows that the average distance from the closest Azteca nest is significantly smaller for the parasitized A. orbigera than for the non-parasitized ones. The result of the second test suggests that Pseudacteon sp. can interfere with the negative effect that A. instabilis has on the parasitoids of A. orbigera.  In other words, this is a cascading trait mediated indirect effect. This is because Pseudacteon sp. reduces the foraging activity of A. instabilis, creating a window of opportunity for the parasitoids of A. orbigera.