Researchers tracked the bumblebees' movements using RFID tags attached to them. (Kimmo Kaakinen via SWNS)
By Stephen Beech
Bees are losing their way due to a chemical used in insect repellents, according to a new study.
Even brief exposure to the insecticide used in mosquito sprays can "significantly impair" bumblebees' ability to navigate their way back to their nest, suggest the findings.
The pollinators' ability to find their way back home is vital to the survival of the entire colony, say scientists.
Many people use mosquito repellents In summer to reduce the insects' buzzing and bites.
One solution that has become increasingly popular in recent years is the Thermacell device, which releases vaporized, pyrethroid-based insecticide prallethrin into the air.
Pyrethroid-based insecticides are legal and widely used for professional and amateur pest control, agriculture, and veterinary purposes.
They are synthetic versions of natural pyrethrins and are commonly used to control insects such as flies, ants, fleas, bedbugs, and moths.
Bumblebees were released from their transport cages a kilometer away from their nests. (Kimmo Kaakinen via SWNS)
There has been much discussion in recent years about the effects of the substance on nature and pollinators in particular, but data has been limited.
For the new study, researchers in Finland studied how prallethrin impacts bumblebees' behavior.
Their findings, published in the journal Biology Letters, show that even a brief exposure to the insecticide can significantly impair bumblebees' ability to find their way back to the nest.
Senior research fellow Olli Loukola, from the University of Turku, said: "For bumblebees, returning to the nest is no small matter, on the contrary, it is essential to the survival of the entire colony.
"If the workers cannot find their way back, the nest will not get any food."
The research team studied the behavior of 167 buff-tailed bumblebees.
Boba Jaglicic
The bees were exposed to prallethrin for one, 10 or 20 minutes with a repellent device meant for consumer use, after which the bumblebees were released a kilometer from their nest and their return was monitored for three days.
Loukola said: "The results were clear.
"Of the bumblebees in the control group that were not exposed to prallethrin, 37% returned to the nest.
"The return percent of the bumblebees that were exposed to prallethrin for one minute did not differ from that of the control group.
"However, of the bees that were exposed for 10 minutes, only 17% found their way back, and just 5% of the bumblebees that were exposed to the insecticide for 20 minutes returned to the nest.
"For those individuals that managed to return, the time taken to do so was not prolonged.
"Furthermore, laboratory tests showed that exposure did not increase bumblebee mortality, suggesting that the effect is specifically related to impaired navigation ability rather than direct toxicity."
Nicole Pearce
Researcher Kimmo Kaakinen, also from the University of Turku, said: "Bumblebee colonies depend on workers collecting food, so if they cannot find their way back to the nest, the colony's ability to obtain nutrition deteriorates.
"Over time, this can weaken the nest, reduce the number of new queens and, in the worst-case scenario, result in the death of the entire colony,"
The use of Thermacell devices is permitted in Finland, but is restricted to the immediate vicinity of residential buildings, such as yards and patios.
The devices must not be used indoors or in natural environments, such as forests or national parks.
Kaakinen said: "Prallethrin-based repellents are used in many countries primarily for convenience.
"In some situations, their use may be justified, for example, in the prevention of diseases spread by mosquitoes."
Loukola added: "It is important to conduct a more detailed assessment of the effects of household insecticides on pollinators.
"The study's findings highlight the need to reassess the ecological safety of these products."