Scrutinizing the enemy release hypothesis: population effects of parasitoids onHarmonia axyridisand local host coccinellids in Brazil

摘要

The Enemy Release Hypothesis (ERH) has been a factor influencing the establishment of some exotic species worldwide. We tested if the ERH could be influencing populations of the exotic predatorHarmonia axyridis(Pallas) (Coleoptera: Coccinellidae) in Brazil. During two years, three local predatory coccinellid species andHarmonia axyridiswere sampled inBrassica oleraceain six organic farms in the midwest of the country. Parasitoids were detected by rearing (emerged) and qPCR Melting Curve Analysis (unemerged). Host density-dependence and spillovers were used to evaluate coccinellid population effects of parasitism. Six parasitoid species were found, including two new records for Brazil. AlthoughHarmonia axyridisharbored fewer parasitoid species, parasitism was not lower and parasitoid density-dependence was not weaker on it compared to the local species. Spillovers among hosts occurred both ontoHarmonia axyridisand from it. The ERH was rejected for these parasitoids and, therefore, it did not contribute to the invasiveness ofHarmonia axyridisin Brazil.