Exposure to some types of pesticides (neonicotinoids) that are widely used in agriculture is considered one of the possible causes of the continuous decline of the honeybee (Apis mellifera) population worldwide.
A study by the University of Trento (CIMeC and Physics department) published today in Scientific Reports investigates the harmful effects of Imidacloprid (the most widely used pesticide in the world, which is naturally present in the environment at non-lethal concentrations) on the insect brain.
Scientists found that Imidacloprid impairs memory and navigation in the honeybee and, for the first time, demonstrated that this pesticide also disrupts olfactory abilities.
The use of Imidacloprid, a derivative of nicotine that has been on the market since the 1980s as a safe alternative to DDT, has been regulated by national and EU legislation in recent years, but the debate around its dangerous properties, especially for terrestrial invertebrates and pollinator insects, is still heated and ongoing.
Exposure to high concentrations of this pesticide causes convulsions and death in honeybees, but the study found that it can negatively affect the insects also at lower concentrations. The researchers observed that, despite restrictions imposed by regulations (like the ban on spraying during full bloom in Trentino Aldo-Adige), the assimilation of this pesticide in honeybees is still high, as it is shown by its concentration in the insect brain.
This might occur because farmers do not respect the rules, or because honeybees are exposed to the pesticide in other ways (through dust or guttation, loss of water from leaves) or because it persists in the environment for several months.
«The active substances in this type of pesticides – explained Albrecht Haase of CIMeC – have serious neurotoxic effects: they act on nicotinic receptors in the bees’ synapses and block the information flow at cerebral level. Our study demonstrates that they have harmful effects both on the most advanced brain functions of honeybees and also on the basic, fundamental functions, like olfactory abilities. Honeybees have a very complex chemical communication system that uses pheromones. Small changes in olfactory perception can seriously compromise the life of the colony because they also affect the social organization of the colony and its reproductive capacity. For example, if the colony does not receive information on the sickness of the queen bee, bees will not activate the mechanisms for the creation of new queens and the colony will collapse».
The study by the Laboratory for Neurophysics (CIMeC and Physics Department) uses brain imaging to examine the effects of neonicotinoids on single receptors and single neurons. This is a first step in the framework of a wider project (“Sub lethal effects of neonicotinoids on the honeybee brain: from single neuron imaging to colony studies”) which will also include the study of behavioural consequences in laboratory honeybees and open-air colonies. The project, which received a 3-year funding from the Autonomous Province of Bolzano-Bozen, will also involve the Free University of Bolzano-Bozen (Faculty of Science and Technology) and the Fondazione Edmund Mach.