Two-thirds of Britain’s common larger moth species have declined significantly over the past five decades, researchers in Harpenden have warned.

Rothamsted Research is celebrating half a century of surveying insects with a variety of activities, including an open meeting tomorrow (Tuesday).

Clocking up 50 years of looking at insects, including why they migrate, has been achieved through collecting data via a nationwide network of suction and light-traps.

Researchers have focused on aphids and moths in particular.

Rothamsted’s dataset on such insects is the longest-running for any terrestrial invertebrate group anywhere in the world.

Dr Richard Harrington, head of Rothamsted’s insect survey, said: “We have shown that two-thirds of our common larger moth species have declined significantly over the past 50 years, especially in southern Britain.

“This is worrying as moths are good indicators of the health of the environment and are important components of the food chain.”

Rothamsted has 84 light-traps in a wide range of habitats, with each trap using a 200-watt tungsten bulb.

Information gathered from nationwide traps is presented in web and email bulletins, which are used to guide aphid control programmes.

Richard said: “We have found strong relationships between winter temperature and the time that aphids are first found in our traps, and their abundance.

“We use these relationships to forecast when movement into crops is likely to start. Compared to 50 years ago, many aphids are flying a month or more earlier.”

• The centre’s insect survey celebrates its 50th anniversary tomorrow, Tuesday April 29, with a free talk by Richard from 7.30-9.30pm.