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Biological pest control in the Galapagos forest July 14th, 2019 by

Agronomy is a kind of applied biology, but conservation biologists are now starting to apply some of the tricks from agriculture, as I saw on a recent visit to the Charles Darwin Research Station in the Galapagos Islands. The campus is tucked discretely into one of the world’s strangest forests, where some of the plants that were able to reach these remote islands have evolved into trees. Prickly pear cactus is usually a low-lying plant with paddle-like pads, but in the Galapagos, it has evolved a tall, straight trunk. The Scalesia trees evolved from a daisy-like flower.

Then in 1982, these rare trees were threatened when the cottony scale insect, originally from Australia, invaded the islands and began to feed on its odd collection of forest species, causing the dieback and death of trees. By 1996 the scale insect was attacking 80 plant species in the Galapagos, including 19 threatened ones.

Displays at the Darwin Station proudly explained their efforts to control the Australian scale insect by bringing in one of its natural enemies, a ladybird beetle, also from down under, that preys on the scale. In 1999, the British Embassy funded an insect containment center, where the ladybird was intensively studied before being released on 11 islands in 2003 and 2004. By 2009 the ladybird had hunted the cottony cushion scale down to a much lower population level. The forest was safe. 

The sign at the Darwin Station said that this was an example of biological pest control, but the display failed to mention that this was the second time that the Australian ladybird beetle had come to the rescue of trees. The first time was in California in 1888, when the ladybird was imported to successfully control scale insects in citrus.

So, conservation biology has learned a lesson from agriculture, specifically from biological pest control. It’s only fair: ecology has provided many key insights to agriculture. For example, Darwinian natural selection explains how pests evolve resistance to pesticides. Gene mapping has helped plant breeders to develop new crop varieties faster.

The Darwin Station is now working on other projects to control pests. For example, an introduced fly is attacking the emblematic finches in their nests, and the Darwin Station is taking eggs from the nests of the mangrove finch (the most endangered of the Galapagos finch species) and rearing the chicks by hand, safe from the flies. The Darwin Station is also rearing several tortoise species, protecting them from introduced rats that eat the tortoise eggs. When the tortoises are two-years old they are released, each species to its own home island.

Agriculture has much experience reproducing plants and animals, and controlling pests in ecologically-sound ways. In the future, plant and animal species can be brought back from the brink of extinction, but it will take more than just conserving their habitat. Individual animals will have to be nurtured, helped to breed in higher numbers, and protected from pests. Conservation biology is becoming more hands on, more like farming and ranching. In the future, other lessons from agriculture may also of use to wildlife conservationists.

Scientific names

The finch-killing fly, Philornis downsi

The ladybird beetle, Rodolia cardinalis

The cushiony cotton scale insect: Icerya purchase

Prickly pear, Opuntia echios

MMangrove finch, Camarhychus heliobatis

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