Planet Care

209: Predators as pesticides


Chemical insecticides kill off good insects as they do bad ones, and they poison the ecosystems on which crops and wildlife thrive


Using natural predators such as ladybird beetles as a form of pest control.

In 1888–1889 the vedalia beetle, Rodolia cardinalis, a lady beetle, was introduced from Australia to California to control the cottony cushion scale, Icerya purchasi. This had become a major problem for the newly developed citrus industry in California, but by the end of 1889 the cottony cushion scale population had already declined.

This great success led to further introductions of beneficial insects into the US. A century later, the convergent lady beetles or bugs are a strong solution for the biological control of aphids. They will lay 600-700 eggs in batches of 40-50 close to the pests and during their larval stage, lady beetles will consume 600 aphids each and in doing so they help to protect crops.

Companies like Insect Lore have them for sale in batches of 1500 but often homeowners find them too expensive. The ladybugs should be released within one week of emerging from their pupal stage, preferably in the evening after sundown or in the morning before sunup.

Results of a study, published in June 2018 in Environmental Research Letters, demonstrated for the first time the economic benefit of using natural predators such as ladybird beetles as a form of pest control. The study estimated that cotton farmers in China could save more than US$300 million by doubling the density of ladybirds in their fields.

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