Channel-Hopping Moth Plague: Our Clothes Are Safe, But Mind The Cabbages

Mark Mallott / Rothamsted Research, CC BY

The Conversation

The next great plague has descended, and this time it’s moths. Diamondback moths have been crossing the English Channel over the past fortnight in far greater numbers than usual.

Those of you reaching for moth-balls and carpet sprays, stop. There are only two species of British moth (from a cast of thousands) that damage clothes, and the diamondback is not one of them. You, the reader, really don’t need to worry – unless you grow cruciferous vegetables like cabbages or broccoli.

Plutella xylostella – more commonly known as the diamondback – is one of the world’s most widespread and prevalent agricultural pests; so widespread, indeed, that scientists disagree as to where exactly its native range lies.

Their success belongs in part to their preference as caterpillars for eating plants in the Brassicaceae family. This amazing group of crops (notably the species Brassica oleracea) has been selectively bred over hundreds of years to make use of almost every part of the plant, and now contains many popular vegetables such as cabbages, broccoli, Brussels sprouts and turnips, as well as oil-seed rape. The moths lay eggs on brassica leaves; a week later, caterpillars hatch and start eating. An infested plant can quickly be reduced to little more than leaf stems.

Cross-Channel Travellers

Despite being one of the smallest moth species to occur in the UK, with a wingspan of under 15mm, diamondbacks are capable of dispersing vast distances, using the wind to make up for their small size. Research has shown that without assistance, diamondbacks are only capable of flying 35 metres – yet when carried along by the wind, they may travel hundreds of miles in a single day.

It is this ability to disperse that leads it to British shores. Every summer, adults cross the Channel and attempt to breed in the UK. A number of butterfly and moth species employ this strategy. In some cases, such as the Painted Lady butterfly, the offspring will return south ahead of the winter. For others, including diamondbacks, the offspring will attempt to remain, but British winters are typically too cold for them to survive.

What’s for dinner? Cabbage, broccoli and Brussels sprouts. Yuangeng Zhang / shutterstock

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