The most popular insecticides in agriculture (neonicotinoids) have caused Drosophila sleep, circadian rhythm and memory disorders, according to a study published in the journal Scientific Reports. Neonicotinoids acted on nicotinic acetylcholine receptors in fly brain neurons and interfered with normal signal transduction. Most likely, these insecticides pose such a threat not only to insect pests, but also to other species – including pollinators.
35 percent of the world’s crop production depends on pollinating insects, and their numbers have continued to decline since the last century. Despite this, the most popular insecticides are neonicotinoids, which act nonspecifically and cause damage to all insects at once: both harmful and beneficial. Some of them have even been banned by the European Union, but even there traces of pesticides are still found in bumblebee populations. Neonicotinoids also dissolve well in water, which traps them in ecosystems.
Neonicotinoids have a negative effect on insects through nicotinic receptors in neurons: insecticides bind to them and cause excessive excitation in the brain. Insects have such receptors in the fungal body, the structure of the brain that is responsible for memory. Nicotine receptors are also involved in transmitting visual signals about illumination and setting the biological clock. The effect of neonicotinoids on memory and sleep in insects has not been sufficiently studied.
Researchers at the University of Bristol, led by Kiah Tasman, studied the effects of neonicotinoids on a model insect, the fruit fly Drosophila Melanogaster. Biologists first confirmed the overall negative effects of insecticides on Drosophila: as with bumblebees, flies had reduced life expectancy, motility and fertility after exposure to substances in concentrations used in agriculture.
Biologists also evaluated the effects of insecticides on Drosophila memory and tested how insects can remember odors. Scientists fed them insecticides, then evaluated the memory: combined different odors with electric shocks to create an unpleasant association in flies, and an hour later asked the insects to remember the unpleasant odor. To do this, they were placed in a long sleeve of T-shaped design, where the remaining two sleeves were odors: unpleasant and control. The more Drosophila chose the control odor due to unpleasant associations with the current, the better the memory performance of the group.
Three of the four neonicotinoids, imidacloprid, clothianidin, and thiamethoxam, impaired memory in Drosophila (p <0.05). To assess the role of the fungal body’s nicotinic receptors, which is responsible for memory in insects, biologists partially “turned them off” and repeated the experiment without neonicotinoids. After that, fruit flies also had a reduced ability to remember odors, which indicates the need for these receptors to remember.
The researchers also studied circadian rhythms in Drosophila after insecticide feeding. They used special activity monitors – cells that recorded the mobility of flies, which judged sleep and wakefulness. The same three insecticides significantly disrupted the circadian rhythms of Drosophila (p <0.001). Also, all neonicotinoids caused restless sleep in flies: the number of sleep episodes increased, but each of them became much shorter.
Biologists have also confirmed the role of nicotinic receptors in this process, but already in the neural networks of Drosophila biological clocks: their partial shutdown caused similar effects. Neonicotinoids have also caused disturbances in flies in the cyclic processes of day and night: normally, the processes of their neurons in the biological clock branch more and form connections during the day than at night. However, after exposure to imidacloprid and clothianidin, no such differences between day and night were observed.
Thus, British researchers have been able to show that the most common insecticides have a strong effect on the brain of insects and prevent them from functioning, disrupting the work of nicotine receptors in the structures of memory and the biological clock. Most likely, this also applies to pollinating insects, which are important for agriculture, so the data in this article are a reason to reconsider the use of neonicotinoids and continue the search for more specific insecticides.
In order for Drosophila to sleep well, you can not only eliminate insecticides from their diet, but also lull them. We recently wrote that rhythmic swaying helps fruit flies sleep longer because of getting used to a certain stimulus.