"One-third of the food we eat, and 75 per cent of crop types including all the nice stuff like fruit, require pollination for a maximum crop, so we need to look after them," he told the 200-strong audience at the Herefordshire Wildlife Trust event.
"But we don’t even have a good handle on their numbers as we do with birds and butterflies, which we need in order to target conservation efforts."
The UK has already lost three bumblebee species completely, he said, and gave "at least four" reasons for the decline among the remaining 26 species: disease, climate change, changes in farming and habitat loss, and pesticides.
Goulson’s own recent research has focussed on the latter. In a Sussex farm he studied, an oilseed rape crop was treated with 20 pesticides and two fertilisers, which he described as "normal for farming", as well as the seeds’ treatment with the systemic pesticide thiamethoxam, use of which "has continued to rise even after the EU moratorium on neonicotinoids in 2013", he said.
"Bees are being stressed from all sides and pesticides probably aren’t the biggest problem they face, but they are exposed to a whole cocktail of them. We might need them for farming, but I would like to see them banned from gardens, as the city of Toronto has done."
Bee conservation often focuses on honeybees, which "are good pollinators but are responsible for no more than 30 per cent of UK pollination", he said. "They haven’t worked out the trick of 'buzz pollination' of tomatoes as bumblebees have."
But he said of the commercial trade in bumblebee colonies to glasshouses: "The nests have had diseases and the bees escape, which has annihilated some native species in South America."
Badgers "are big predators of bumblebees – they will dig the nest up and eat the whole thing" – an observation which led the trust to attempt to train bumblebee sniffer dogs to improve monitoring, with mixed results, he said.
Goulson, named number 9 in BBC Wildlife's "top 50 conservation heroes" last year, explained: "Unlike most insects have a high body temperature are adapted to a cold climate – there is even a Bombus polaris in the Arctic. They won’t thrive in a warmer climate and we are already seeing their ranges narrowing."
In urban areas of the southern UK some no longer hibernate due to the presence of exotic flowers and shrubs, he added.
Goulson's tips for boosting bee populations
- "Recreate flower-rich meadows – it takes time but there is a lot of advice. Some flowers are fantastic, others are rubbish. A dog rose is good, but in a modern highly-bred rose the anthers grow as extra petals."
- "Don't buy highly bred annual bedding plants - no insects go near them as they are weird shapes and have lost their scent. But traditional cottage garden plants instead, which are mostly perennial and fairly bulletproof."
- "Grow some native annuals from seed if you can, such as viper's bugloss which bees love."
- "Put up a bee hotel for solitary bees – there are glass-sided ones that let you see what’s going on inside.
- "Badger the council to manage their land differently. They have so much mown ground. Our ‘On The Verge’ project in Stirling has converted much of that to wildflowers."
- "Get involved in The Buzz Club, a citizen science project generating usable data on pollinators."