Post release evaluation of Rodolia cardinalis (Coleoptera: Coccinellidae) for control of Icerya purchasi (Hemiptera: Monophlebidae) in the Galápagos Islands

Abstract

Post-release field evaluations (2009–2011) of the impacts of Rodolia cardinalis (Mulsant) (Coleoptera: Coccinellidae) released in the Galápagos Islands in 2002 for the classical biological control of Icerya purchasi Maskell (Hemiptera: Monophlebidae) indicated that substantial (∼60–98% reduction in I. purchasi densities) and persistent suppression of this pest has occurred. Most endemic and native plants surveyed appear to no longer have heavy I. purchasi infestations nor disfiguring honeydew contamination. However, pest suppression by R. cardinalis was less successful on some plant species, such as the native sand dune-inhabiting Scaevola plumieri (L.) Vahl. on which substantial, but fluctuating I. purchasi densities remain. In urban areas, invasive ant species tending I. purchasi colonies likely interfered with biological control. In 22h of field cage observations of R. cardinalis foraging on native plants infested with various combinations of five non-target arthropod species and I. purchasi, no attacks on non-target prey occurred. In field cages, all observed attacks and feeding activity were on I. purchasi. Captures of R. cardinalis were significantly higher on yellow sticky traps placed in plants infested with I. purchasi compared to plants that were not hosts of I. purchasi. We conclude that the first biological control project in the Galápagos Islands with R. cardinalis against I. purchasi has been very successful and R. cardinalis is highly unlikely to affect non-target species following its establishment and spread in the archipelago.