Galapagos Invasive Species:
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Good bugs: Biological control of the cottony cushion scale

The cottony cushion scale (also known as the Australia bug) Icerya purchasi has invaded more than 80 countries worldwide, damaging more than 2000 species of plant. In 1982 it was reported for the first time in Galapagos, where it is locally known as “pulgon”. In Galapagos, the cottony cushion scale threatens at least 69 species of native and endemic plant, as well as some crops, particularly citrus. The scale was killing the button mangrove, five endangered species and 19 threatened species of plant.

Cottony cushion scale The biological control programme for the cottony cushion scale is the first example of classic biological control in Galapagos. For the first time an organism has been deliberately introduced to the archipelago. The agent used was the ladybird, Rodolia cardinalis, locally known as the “mariquita”.. The first individuals were released on 25th January 2002. The release of the mariquita was authorised by the Technical Committee of the Galapagos National Park (GNP) after the Charles Darwin Foundation (CDF) had demonstrated that there was no risk of non-target impact, following four years of intensive work carrying out risk analyses. Scientists of the CDF and park rangers with the GNP made the first release simultaneously on the inhabited islands of Santa Cruz, San Cristóbal, Isabela and Floreana. Subsequently, releases have been made on uninhabited islands and zones, such as Tagus cove and Alcedo volcano on Isabela, the peak of Fernandina, Marchena, Pinta, Pinzon, Rabida, Genovesa and Santiago islands. Up to November 2004, a total of 2024 adults, 27 pupas and 5 larvae have been released.

Samples taken in Puerto Ayora in Santa Cruz demonstrate the high dispersion ability of the mariquita; individuals were found feeding on the cottony cushion scale on a variety of plants around the urban perimeter, and were also found up to 40km from the release points, on the islands of Baltra, North Seymour and El Eden. Studies carried out by the CDF and GNP have found that the mariquita had established successfully in more than half of the release sites, and had significantly reduced the populations of cottony cushion scale in at least two release sites.

The GNP and the CDF will continue to monitor the distribution of the mariquita, and to release more individuals, until the population has become established and control of the pest cottony cushion scale is secure. However, it is expected that the CDF will need to continue producing and releasing mariquita for an extended period, especially for sites with adverse climatic conditions where Rodolia cardinalis has difficulty establishing itself.

Source: Charles Darwin Foundation and the Galapagos National Park.

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This website was created on 25 October 2004 by PT and JK