Sandy's Garden ... The Colorado Beetle

I was browsing idly through a 30-year-old book about companion planting recently.

By James Trimble
Monday, 20th July 2020, 9:16 am
Updated Monday, 20th July 2020, 9:16 am

Companion planting is defined in Wikipedia as ‘the planting of different crops in proximity for any of a number of different reasons, including pest control, pollination, providing habitat for beneficial insects, maximizing use of space, and to otherwise increase crop productivity’.

Then I encountered once-familiar words which I have not met for many a year. These words were ‘Colorado beetle.’ The book was concerned with encouraging the potato-growing gardener … which I am not … to grow plants which would be even more attractive to this pest than potatoes, or plants which would encourage the beetle’s natural predators to drop by, or plants which actually repel the beetles.

Whatever the gardener of the past’s choice, it would not have found official favour in the UK today where immediate action is now required. The Department of the Environment, Food and Rural Affairs (DEFRA) says … about Leptinotarsa decemlineata … ‘The Colorado beetle is not established in the UK and is a notifiable quarantine pest, whose introduction is prohibited under the EC Single Market Protected Zone arrangements for Plant Health.

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Falkirk Herald gardening guru Sandy Simpson

It is important to remember that a breeding colony could be established by a single fertilised beetle escaping detection.’ DEFRA offers comprehensive advice to companies which import potatoes into the UK and overseas companies which export potatoes to the UK as well as to wholesale distributors, including posters and leaflets to ensure that all staff can recognise Colorado beetles and know what must be done immediately if even a single beetle is found.

So what is this pest and how would you, gentle reader, recognise it in the very unlikely event of your encountering one in the garden? Adult Colorado potato beetles have striped yellow and black backs, with orange heads showing black dots.

They are about the size of a fingernail and are very distinctive. First described in 1824 by Thomas Say, who found them in the Rocky Mountains, the insect's association with the potato plant was not known until about 1859 when it began destroying potato crops about 100 miles west of Omaha, Nebraska.

The insect then started its rapid spread eastward, reaching the Atlantic Coast by 1874. Nowadays, the pest is endemic to Mexico, most of the United States, southern Canada and Central America. It has also been exported to parts of Europe and of Asia.

It is thought that the Colorado beetle actually evolved in central Mexico and it had a selection of names in the United States … the ten-striped spearman, ten-lined potato beetle, potato-bug and the new potato bug … prior to 1867, when the name ‘Colorado potato beetle’ found favour after a large outbreak of these pests occurred in that state and it was mistakenly assumed that this was their natural home.

Today, the Colorado beetle is a major potato pest throughout North America, where the adults and the larvae …the caterpillars which are the intermediate stage between eggs and adult beetles … feed greedily on the leaves of plants in the nightshade family, particularly potatoes, and can completely defoliate plants, precluding the expected crop.

Most pesticides are ineffective against them; and American gardeners and farmers alike are told to hand pick larvae and adults off plants and drop them into a container of soapy water. Now there’s a real task, hand picking bugs off plants in a field of potatoes!

It’s many years since I last saw a warning about Colorado beetles in the UK, so I assume that DEFRA’s instructions are being strictly observed by the potato industry and that these pests are being prevented from migrating to this country.

But in the very unlikely event that you think you have found one, catch it and e-mail [email protected]