Non-contact exposure to dinotefuran disrupts honey bee homing by altering MagR and Cry2 gene expression

Dinotefuran is known to negatively affect honeybee (Apis mellifera) behavior, but the underlying mechanism remains unclear. The magnetoreceptor (MagR, which responds to magnetic fields) and cryptochrome (Cry2, which is sensitive to light) genes are considered to play important roles in honey bees’ homing and localization behaviors. Our study found that dinotefuran, even without direct contact, can act like a magnet, significantly altering MagR expression in honeybees. This non-contact exposure reduced the bees’ homing rate. In further experiments, we exposed foragers to light and magnetic fields, the MagR gene responded to magnetic fields only in the presence of light, with Cry2 playing a key switching role in the magnetic field receptor mechanism (MagR–Cry2). Yeast two-hybrid and BiFc assays confirmed an interaction of these two genes. Moreover, the bees’ homing rate was significantly reduced when the expression of these genes was decreased using RNAi. These findings suggest that changes in MagR and Cry2 expression are critical to the reduction in homing ability caused by non-contact dinotefuran exposure. This study reveals the potential navigation mechanisms of honey bees during homing and foraging and shows that the impact of dinotefuran on honey bee populations is more extensive than previously understood.

Honey bees are among the world’s most economically important insects, playing a crucial role as pollinators in plant growth. One colony consists of a queen, drones, and foragers, with the worker bees being essential for providing food for the entire colony [1]. However, since Colony Collapse Disorder (CCD) was first reported in 2006, honey bee populations have been severely affected [25]. CCD has been linked to various factors, including pesticides, parasites, and lack of nectar plants [11]. Recent research also suggests that CCD may be related to electromagnetic waves, with radiation from cell phone towers and mobile handsets potentially causing harm to honey bees [18]. These external environmental factors can disrupt honey bees’ outdoor navigation, leading to their failure to their nests. However, the exact mechanisms behind honey bee navigation remain unclear.

Foragers have a wide range of activity, with a radius extending up to 2–3 km (He et al., 2013). Honey bee has ability to navigate due to their ability to tell the location by sun and sky. Also, they can locate using earth magnetic field[15], [24], [30], [5]. Gould et al. [10] first proposed the presence of magnetite particles in bees. These magnetic receptors are believed to be the physiological basis for many honey bee behaviors. Experiments by Vale & Acosta-Avalos [38] and Migdał et al., [22] have shown that changes in magnetic fields can affect honey bee flight behavior and navigation. Additionally, Walker and Bitterman [40] and Kirschvink et al., [16] found that honey bees can perceive static magnetic fields as weak as 26 nT and alternating magnetic fields of 10–60 Hz during free flight. Further research by Hsu and Li extracted magnetite particles from the trophoblast cells of honey bees, revealing that these particles contract or expand horizontally or vertically in response to magnetic field changes. Using a superconducting quantum interference detector, they also discovered remanent magnetism in the honey bee abdomen [14], [26], [31], [43]. With advances in molecular technology, Zhao et al., [51] cloned the magnetoreceptor (MagR) gene in Apis mellifera, a member of the iron–sulfur cluster family of proteins, which plays a key role in the MagR sensing mechanism [42].

The cryptochrome (Cry) protein gene was first discovered in cryptogamous plants, which led to its name [12]. As a photoreceptor, Cry is sensitive to blue-green light [32]. Cry contains a blue light-absorbing cofactor, flavin adenine dinucleotide (FAD), which interacts with tryptophan on Cry through a series of light-induced electron transfers. This interaction produces a “free radical pairing” reaction, which regulates Cry’s signaling activities. [45] demonstrated that Cry contributes significantly to the migratory navigation of birds [45]. Studies on Arabidopsis thaliana, Drosophila, monarch butterflies, birds, and humans have shown that Cry can sense magnetic fields [13], [2], [41], [44], [46], [9]. Over time, Cry in insects has evolved into two main families: Cry1 and Cry2. While Drosophila has only Cry1, insects such as mosquitoes and butterflies possess both Cry1 and Cry2 [52]. However, honey bees have only Cry2 due to their biological circadian rhythms [47]. Many studies have explored how bees use light for outdoor localization. Kobayashi et al. [17] recently showed that honey bees can use polarized sunlight for orientation. They sense light at specific angles to determine their flight direction and orientation.

Dinotefuran, a third-generation neonicotinoid insecticide, was first registered in Japan in 2003 [39]. Recent studies have shown that dinotefuran can be found in the pollen and nectar of pollinating plants(in pumpkin: average levels up to 122 μg/L in pollen and 17.6 μg/L in nectar, in the nectar of plants in urban landscapes: 70 -1235 μg/L) [21], [7], posing a significant threat to bee survival. S-dinotefuran, the chiral form of +dinotefuran, is more toxic than R-dinotefuran [19], [50]. Consequently, some researchers have recommended using R-dinotefuran as an insecticide to reduce the risk to honey bee populations [4]. Additionally, dinotefuran negatively affects bees’ learning and memory abilities when they are exposed orally or percutaneously [19]. However, there is limited research on the impact of non-contact exposure to dinotefuran on honey bee homing.

In our previous study, we found that feeding dinotefuran significantly elevated the body temperature of honey bees, altered their social behaviors such as antennation and trophallaxis, and accelerated the homing of honey bees [48]. However, our subsequent study found that dinotefuran could significantly affect the homing behavior of honey bees under non-contact conditions, and for the first time, we found that dinotefuran under non-contact conditions could cause alterations in the genes of the MagR and Cry2 in honey bees. Therefore, we carried out in-depth studies with the aim of revealing the effects of dinotefuran on the behavior of honey bees under non-contact conditions and the main mechanisms.