Audrey, A., Grez, A.A., Zaviezo, T., Soares, A.O., Romero, V. & González, C. (2019) Field and laboratory evidence of mechanisms explaining the dominance of Harmonia axyridis (Pallas) in alfalfa in Chile. Proceedings of the fourth meeting “Benefits and Risks of Exotic Biological Control Agents” IOBC-WPRS Bulletin, 145, 50-52. ISBN:978-92-9067-330-9.
Harmonia axyridis Pallas is native to Asia, and it was introduced to many regions of the world for biological control of aphids. Then, an invasive strain was generated in eastern North America and this expanded to almost all continents, including Chile where it has rapidly spread along the country (Lombaert et al., 2014; Roy et al., 2016). One of the main negative consequences of the arrival of H. axyridis in these parts of the world has been the decline of native species (Roy et al., 2012; Brown and Roy, 2018). In alfalfa fields in Central Chile, coccinellids assemblages used to be very diverse and dominated by native species, which accounted for most of aphid predation (Ximenez-Embun et al., 2014). But, after the invasion of H. axyridis, coccinellids declined in abundance and diversity, possibly due to antagonistic interactions (Grez et al., 2016). Harmonia axyridis today dominates coccinellid assemblages in alfalfa fields. As possible mechanisms explaining the success of this species in Chile, we studied intraguild predation (IGP), interspecific competition and the scape from parasitism in the most common coccinellids in this crop: the native Eriopis chilensis Hofmann and the aliens H. axyridis and Hippodamia variegata (Goeze) (Figure 1).
IGP was studied both in the laboratory and in the field. In the laboratory, we exposed adults of each coccinellid species to eggs of the other two species separately and counted the number of eggs predated. In the field, we used sentinel eggs of the three species glued to transparent cards and observed the number of cards with predation. Also, in the field we collected adults and evaluated IGP through molecular gut content analyses (Singleplex PCR for COI). Interspecific competition was studied in the laboratory. The daily per capita voracity and the proportional weight gain of coccinellid species were estimated when individuals were alone or in conspecific and heterospecific groups of three individuals, under a limited amount of aphids. To determine whether H. axyridis was less susceptible to parasitism by Dinocampus coccinellae (Schrank) compared to the other two species, we collected at least 100 individuals from each species from different alfalfa fields, kept them for 35 days until the appearance of the parasitoid pupa or dissected them to detect larvae inside their bodies. To determine oviposition in the laboratory, all three species were exposed to the parasitoid for 1 hour, and then dissected to detect eggs.