Declines in the biodiversity of pollinating insects and wild plants have slowed in recent years, according to researchers from the University of Leeds and a Dutch research institute.

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Researchers led by teams at the University of Leeds and Naturalis Biodiversity Centre in the Netherlands said their findings are "encouraging". They uncovered evidence of dramatic reductions in the diversity of species in Britain, Belgium and the Netherlands between the 1950s and 1980s, but also revealed that the rate of declines slowed after 1990. Though declines slowed, overall biodiversity losses continued among species of bees, hoverflies and wild plants.  

Professor Bill Kunin, Professor of Ecology at the University of Leeds, elaborated, "Most observers have been saying that the 1992 Rio Earth Summit targets to slow biodiversity loss by 2010 failed, but what we are seeing is a significant slowing or reversal of the declines for wild plants and their insect pollinators.

"These species are important to us. About a third of our food production, including most of our fruit and vegetables, depends on animal pollination and we know that most crop pollination is done by wild pollinators. Biodiversity is important to ensuring we don't lose that service. Relying on a few species could be risky in a changing environment," he added.

The researchers, working with funding from the EU STEP programme which aims to protect insect pollinators, found a 30 per cent fall in local bumblebee biodiversity in all three countries between the 1950s and the 1980s. However, that decline slowed to an estimated 10 per cent in Britain by 2010, while in Belgium and the Netherlands bumblebee diversity had stabilised.

The picture was better for other wild bees, with an 8 per cent reduction in diversity in the Netherlands and a stable picture in Great Britain turning into significant increases (7 per cent in the Netherlands and 10 per cent in Britain) over the past 20 years. While these solitary bees continued to decline in Belgium, diversity of hoverflies (also important pollinators) improved there, shifting from stable diversity in the 1980s to significant (20 per cent) increases in recent decades. British wildflower diversity had declined about 20 per cent from the 1950s to the 1980s, but again the declines have ceased in the past 20 years, the researchers said.

Not all groups fared so well. Butterfly diversity continued to fall in all three countries at roughly the same rates as in the past. In April, butterfly conservationists at the Centre for Ecology and Hydrology revealed that 2012 had been the worst year on record for butterfly populations in the UK, with butterfly abundance reaching all-time lows and massive population declines for some of the country's rarest species, meaning they now face extinction on UK shores.

Lead author cautiously suggests Rio 1992 targets may be effective

Dr Luisa Carvalheiro, lead author on the paper, explained that the study's findings may illustrate a rather depressing scenario; she said, "It is possible that by 1990 the most sensitive species had already gone," though she added, "that's probably not the whole story, as there are still plenty of rare and vulnerable species present in recent records."

Dr Carvalheiro speculated, "There is a much more encouraging possibility: the conservation work and agri-environment programs paying farmers to encourage biodiversity may be having an effect. We may also be seeing a slowdown of the drivers of decline. The postwar emphasis on getting land into production and on more intensive farming has given way to a more stable situation in which the rate of landscape change has slowed and in which agrichemical excesses are regulated."

"If what we take from the Rio targets is that the investment in conservation gave us no results, then that is a counsel of despair. This study brings a positive message for conservation. But some important groups are undoubtedly still declining, so continued and increased investment in conservation practices is essential for guaranteeing the persistence of a diverse assemblage of species," she added.

Co-author Professor Koos Biesmeijer, who works both at the University of Leeds and Naturalis, said the research "reveals much more detail about the scale and timing of biodiversity losses," though he continued, "However, while we can use biodiversity records to measure changes in the diversity of pollinators, we can't tell what's happening to their overall abundance or to the quality of the pollination services they provide to wildflowers or agricultural crops. To study these issues would require a long-term monitoring programme."

Following the official announcement that the EU will restrict use of three neonicotinoid pesticides from December this year over concerns their use is contributing to bee decline, the bloc's health watchdog EFSA yesterday released the results of a risk assessment investigation which found that a fourth insecticide, the phenylpyrazole pesticide fipronil poses a "high acute risk to honeybees."