Evaluating the safety of Rodolia cardinalis to two species of Galapagos finch; Camarhynchus parvulus and Geospiza fuliginosa

Abstract

Some species of coccinellids exude a fluid that contains an alkaloid which can be toxic to vertebrates that ingest them. Because of this, before introducing Rodolia cardinalis to the Galapagos Islands as a biological control agent for the invasive scale insect, Icerya purchasi, it was considered necessary to determine whether it is toxic to birds. In this study, experiments were carried out with two common, insectivorous finches that are endemic to the Galapagos Islands; Camarhynchus parvulus (12 individuals) and Geospiza fuliginosa (16 individuals). Finches were maintained in captivity for 12–18 days. This period was divided into three phases: adaptation, experimental, and observation. During the experimental phase, test individuals, in addition to their regular diet, were fed 0.15 g portions of larvae or adults of R. cardinalis on alternate days over four days. The control group were fed 0.15 g of Asciodes quietalis abdomens in place of R. cardinalis. Symptoms of toxicity (mortality, deterioration, critical weight loss) from feeding on R. cardinalis were not observed in either species while in captivity, but birds avoided or rejected beetles indicating that they were distasteful. Finches regurgitated a higher number of larvae than adult beetles suggesting that larvae were less palatable than adults. Although long-term monitoring was not possible, results suggest that at least two species of finch will be unaffected by the release of R. cardinalis into the Galapagos Islands.