Pesticides used to protect crops from insects are keeping bees awake, according to new research, writes Mark Raghorn.

The vital pollinators need a good night's sleep to function properly but exposure to neonicotinoids - the most common insecticide used worldwide - disrupts their circadian rhythm.

It causes them to lose their sense of time and navigation - leading to lower survival rates, say neuroscientists at the University of Bristol.

Studies found the chemicals reduced both bumblebees' and fruit flies' quality rest - shedding fresh light on why they are vanishing from the wild.

Lead author Dr Kiah Tasman said: "The neonicotinoids we tested had a big effect on the amount of sleep taken by both flies and bees.

"If an insect was exposed to a similar amount as it might experience on a farm where the pesticide had been applied, it slept less, and its daily behavioural rhythms were knocked out of synch with the normal 24-hour cycle of day and night."

Similar to our circadian rhythm, honeybees sleep between five and eight hours a day. And, in the case of forager bees, this occurs in day-night cycles.

This means more rest at night when darkness prevents their excursions for pollen and nectar.

Co-author of the study published in the journal Scientific Reports, Dr James Hodge said: "Being able to tell time is important for knowing when to be awake and forage, and it looked like these drugged insects were unable to sleep.

"We know quality sleep is important for insects, just as it is for humans, for their health and forming lasting memories."

Experiments on fruit flies revealed the impact of the pesticides on the insect brain.

Typical agricultural concentrations ruined their ability to remember.

The researchers also saw changes in the clock in the fly brain which controls its 24-hour cycle of day and night.

Explained co author Dr Sean Rands: "Bees and flies have similar structures in their brains.

"This suggests one reason why these drugs are so bad for bees is they stop the bees from sleeping properly and then being able to learn where food is in their environment.

"Neonicotinoids are currently banned in the EU, and we hope this continues in the UK as we leave EU legislation."

But they still make up nearly a quarter of the global insecticide market - worth a billion dollars a year (£730million).

Their intensive use has been linked with the worldwide decline in pollinating insects. All four major types of neonicotinoid have largely been banned in the EU and currently in the UK.

They affect their nervous systems, stimulating similar receptors in bees' brains to those targeted by nicotine in humans - and providing the same buzz.

Last year a study by a US team found small levels of neonicotinoids led bees to have barely any sleep at all.

Scans showed the chemicals accumulate in the bee brain - harming neurons that control the body clock.

Previous research has shown the insects cannot communicate properly if they don't get enough sleep.

Instead of performing their waggle dances with incredible accuracy, sleepy bees become sloppy.

Their interpretive dances fail to translate the direction of a profitable food source.

And since their nest mates use this information as a guide for their foraging trips, they are likely to be sent slightly astray, wasting time and energy on the wing. The whole colony suffers.

Sleep-deprived honeybees also find it difficult to return to the hive when visiting fresh flower patches. Many even get lost and never return.

In humans, deep sleep (known as slow-wave sleep) consolidates memories, transferring them from short-term to long-term memory. This is thought to apply to bees.