A species of bee believed to be extinct in Britain has been found after 65 years, a study has revealed.

The solitary bee Halictus eurygnathus was last seen in Britain in 1946, but has now been found at seven sites in East Sussex, according to research by entomologist Steven Falk.

He said: "I discovered that the main requirement of the bee is an abundance of greater knapweed, which is one of the special flowers of chalk grassland. This knowledge should be helpful for the conservation of this species."

His study recorded 227 bee and wasp species during dozens of visits to 15 chalk grassland and chalky heath sites on the East Sussex South Downs.

Mr Falk said many of the species he recorded were "very rare" and some were doing better than expected.

But others, including one of Britain's largest mining bees, Andrena hattorfiana are in trouble, he warned.

His report also reveals the importance of arable field margins with wildflowers and blackthorn for foraging bees, with one of Britain's rarest mining bees Andreana niveata foraging primarily on flowers of charlock and hedge-mustard at the edges of rape crop, a relationship which had not been seen before.

Duncan Sivell, biodiversity officer at wildlife charity Buglife, said: "This report provides a wealth of information on bees and wasps on the South Downs; species that were thought extinct have been rediscovered, declines in other species have been identified and new behavioural patterns have been recorded.

"These results highlight the importance of survey work, which is badly under-funded."