Retailers have clarified their stance on pesticide use after new research revealed a combination of two commonly used products harmed bumblebee populations.

The research - published earlier this week - found that the use of imidacloprid and lambda-cyhalothrin affected the foraging behaviour of bumblebees, leading to increased bee deaths and the collapse of colonies in some cases.

The Co-operative Group said imidacloprid was a neonicotinoid that was on its “prohibited list”, which applied to fresh and frozen produce sold in store and grown on its farms. “Farmers have to request permission to use it and demonstrate that they don’t have viable alternatives,” said a spokeswoman. Lambda-cyhalothrin, in contrast, was on the retailer’s “monitor list”, she added.

Morrisons said it understood the importance of encouraging healthy bee populations in the UK and screened all pesticides used by its suppliers to ensure they did not have an adverse effect on bees. “The two pesticides mentioned are not used together in the UK by Wm Morrison suppliers on crops that might attract bees,” a spokesman said.

Tesco, meanwhile, said it did not use the two pesticides in combination on any “flowering crops” such as apples or pears in the UK. “We take the issue of bee health seriously and have extra restrictions on the use of pesticides so they have the minimum effect on beneficial insects like bees,” said a spokesman.

Sainsbury’s did not respond to specific questions over whether its suppliers were permitted to use the two pesticides mentioned in the study. A spokeswoman, however, said: “Our pesticide policy requires our suppliers to minimise their use of pesticides and employ Integrated Crop Management techniques.” The policy included a section on Sainsbury’s “expectations” for protecting pollinating insects and bees, she added.

The research was carried out by Royal Holloway College, University of London and was published by Nature, an international science journal.