The impact of an exotic social wasp (Vespula germanica) on the native arthropod community of NW Patagonia, Argentina: An experimental study

SACKMANN, PAULA; FARJI-BRENER, AG; CORLEY, J

ECOLOGICAL ENTOMOLOGY

WILEY-BLACKWELL PUBLISHING, INC

Año: 2008 vol. 33 p. 213 - 224

0307-6946

1. Biological invasiones are usually thought to have a negative impact on native communities. However, data supporting this idea is often based on comparative studies between invaded and not invaded areas, and spatially and temporally limited. 2. We  experimentally assess the impact of an exotic wasp, Vespula germanica, on the native arthropod community of NW Patagonia during 3 years in a area of 80 has. V. germanica is an exotic social vespid that has invaded NW Patagonia twenty years ago. It has been suggested that its populations affect native arthropods because of its broad diet and also because Patagonia lacks natural enemies and potential competitors for these wasps. 3. Using wasp specific toxic baits, we reduced V. germanica abundance in 5 sites of native woodlands (covering 80 has. in total) during 3 consecutive years. We then compared the abundance, species richness and composition of arthropods between non-poisoned (control) and poisoned sites, both before and after wasp poisoned. 4. Wasp abundance represented 6% of the total arthropod catches in non-poisoned sites and was reduced, by 50% on average, in the treated areas. The abundance, species richness and composition of the arthropod community (305 species, 24600 individuals) did not differ between non-poisoned areas and areas where V. germanica was poisoned. Significant differences in response variables were found only before wasp poisoning has begun and were related to varitions among sites.  5. These results suggest that Vespula germanica is not affecting the local arthropod assemblages, contradicting past work in other regions. The low relative abundance of wasps in Patagonia, when compared to other invaded regions, might explain our findings. 6. Our work provides further evidence on the importance of large scale exprimental work with before/after comparisons to fully understand the impact of invaders on natural communities.